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"squall line" Definitions
  1. an intersection or boundary between the cold and the warm winds of an extratropical cyclone or between the cold air of an advancing anticyclone and the warm air of a cyclone : COLD FRONT
  2. a line of squalls often 50 to 200 miles ahead of a cold front
"squall line" Synonyms
line squall squall storm tempest tropical storm wind-shift line cold front snap cold snap cold spell cold wave cold sector polar front

284 Sentences With "squall line"

How to use squall line in a sentence? Find typical usage patterns (collocations)/phrases/context for "squall line" and check conjugation/comparative form for "squall line". Mastering all the usages of "squall line" from sentence examples published by news publications.

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Early in the day a squall line moved through Texas, bringing 80-mph wind gusts to the Dallas metro region.
We received many reports of wind damage due to straight-line winds as a squall line tracked east early this morning.
The forecaster added that "we can't rule out" this squall line surviving until the mid-Atlantic states on Thursday, causing wind gusts and severe weather in Washington, D.C., and Philadelphia.
The storm was likely to come in two waves, a morning cluster of thunderstorms in the Upper Mississippi and Ohio valleys followed by a single squall line pushing east across Indiana, Ohio and Michigan by the evening, according to The Weather Channel.
This leads to an erosion of rain within the broad rain shield behind the squall line, and may lead to acceleration of the squall line itself.
How a squall line is depicted by the NWS on weather maps Squall lines are depicted on National Weather Service surface analyses as an alternating pattern of two red dots and a dash labelled "SQLN" or "SQUALL LINE".
Following the initial passage of a squall line, light to moderate stratiform precipitation is also common. A bow echo is frequently seen on the northern and southernmost reaches of squall line thunderstorms (via satellite imagery). This is where the northern and southern ends curl backwards towards the middle portions of the squall line, making a "bow" shape. Bow echoes are frequently featured within supercell mesoscale systems.
September 3, the USS Shenandoah encounters a squall line in Ohio and crashes.
Usually, this sudden violent wind is associated with briefly heavy precipitation as squall line.
Cyclonic vortex over Pennsylvania with a trailing squall line A squall line is an elongated line of severe thunderstorms that can form along or ahead of a cold front. The squall line typically contains heavy precipitation, hail, frequent lightning, strong straight line winds, and possibly tornadoes or waterspouts. Severe weather in the form of strong straight-line winds can be expected in areas where the squall line forms a bow echo, in the farthest portion of the bow. Tornadoes can be found along waves within a line echo wave pattern (LEWP) where mesoscale low-pressure areas are present.
Once new thunderstorm activity along the squall line concludes, the wake low associated with it weakens in tandem.
Once new thunderstorm activity along the squall line concludes, the wake low associated with it weakens in tandem.
A weather radar image of a Cyclonic vortex over Pennsylvania with a trailing squall line A squall line or quasi-linear convective system (QLCS) is a line of thunderstorms forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts. Strong straight-line winds can occur where the squall line is in the shape of a bow echo.
Another term that may be used in association with squall line and bow echoes is quasi- linear convective systems (QLCSs).
A later squall line contributed to additional tornadoes and a widespread swath of damaging winds as the system tracked eastward.
Further south, considerable damage took place across Missouri and Arkansas due to a squall line. Gusts reached in Hannibal, Missouri. One person was killed in Springdale, Arkansas after his vehicle was struck by wind-driven debris. Several tornadoes touched down within this squall line in the two states, none of which exceeded EF1 intensity.
Throughout the afternoon, numerous supercell thunderstorms that formed ahead of the squall line produced several significant and damaging tornadoes, including the violent EF4 that struck Beauregard, Alabama. As the squall line moved eastward, embedded circulations and semi-discrete structures within the line produced additional strong tornadoes before tornadic activity waned with eastward progression overnight.
A squall line is an elongated line of severe thunderstorms that can form along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. The squall line contains heavy precipitation, hail, frequent lightning, strong straight line winds, and possibly tornadoes and waterspouts. Severe weather in the form of strong straight-line winds can be expected in areas where the squall line itself is in the shape of a bow echo, within the portion of the line that bows out the most.
Nearly continuous supercells formed north of the Gulf of Mexico and produced many tornadoes, some of which hit large population centers with devastating effects. Those tornadoes killed twenty people. Map of the 14 confirmed tornadoes in central Georgia The squall line finally overtook the supercells just after midnight on March 2, after putting down 37 tornadoes that day. As the squall line overtook the cells, a few tornadoes — all EF0 — took place overnight in Florida and extreme southern Georgia within the squall line, before the severe weather emerged in the Atlantic Ocean that morning.
The squall line finally moved out of Cuba near sunrise, leaving 10 deaths and US$1 billion in damage on the island.
The cold air outflow leaves the trailing area of the squall line to the mid-level jet, which aids in downdraft processes.
Despite the squall line remaining intact, several more tornadoes developed. Several more tornadoes developed on March 30 and 31 before the system weakened.
The Derecho moves into the Florida coast during the overnight hours of March 13, 1993 NOAA estimate of storm surges along Florida's Gulf Coast, March 13, 1993. Besides producing record- low barometric pressure across a swath of the Southeast and Mid-Atlantic states, and contributing to one of the nation's biggest snowstorms, the low produced a potent squall line ahead of its cold front. The squall line produced a serial derecho as it moved into Florida and Cuba shortly after midnight on March 13. Straight-line winds gusted above at many locations in Florida as the squall line moved through.
As supercells and multi-cell thunderstorms dissipate due to a weak shear force or poor lifting mechanisms, (e.g. considerable terrain or lack of daytime heating) the squall line or gust front associated with them may outrun the squall line itself and the synoptic scale area of low pressure may then infill, leading to a weakening of the cold front; essentially, the thunderstorm has exhausted its updrafts, becoming purely a downdraft dominated system. The areas of dissipating squall line thunderstorms may be regions of low CAPE, low humidity, insufficient wind shear, or poor synoptic dynamics (e.g. an upper-level low filling) leading to frontolysis.
A severe squall line pushed through the southern part of Iowa, causing a long swath of widespread wind damage and power outages. Two people were injured in Indianola while another was injured in Ottumwa. Seven hereford cows were also killed by lightning in Mt. Vernon as well. Another severe squall line moved through Milwaukee, Wisconsin, with high winds damaging buildings and vehicles.
The squall line continued to produce a few more tornadoes, in addition to large hail and damaging straight-line winds. On June 14, the squall line continued to produce wind damage, as well as producing a few more weak tornadoes in Wisconsin, all of which did relatively minor damage. Overall, this outbreak produced 40 tornadoes and did not result in any fatalities.
Tornadoes are only occasionally reported. In certain conditions, squall line can extend on a very long line, moving extremely rapidly, and become a derecho.
In mid-latitude regions, convective precipitation is often associated with cold fronts where as it is often found behind the front, occasionally initiating a squall line.
From here, a general thinning of a squall line will occur: with winds decaying over time, outflow boundaries weakening updrafts substantially and clouds losing their thickness.
On April 14, the system rapidly dissipated, as it was absorbed into a large squall line. This is the only recorded tropical cyclone in the eastern South Atlantic.
It also was unusual because it was not associated with such a squall line at all, but was an independent supercell well ahead of the main storm system.
These clouds are the result of former cumulonimbus clouds having disintegrated, or an area of only minor instability ahead of the main squall line. As supercells and multi-cell thunderstorms dissipate due to a weak shear force or poor lifting mechanisms, (e.g. considerable terrain or lack of daytime heating) the gust front associated with them may outrun the squall line itself and the synoptic scale area of low pressure may then infill, leading to a weakening of the cold front; essentially, the thunderstorm has exhausted its updrafts, becoming purely a downdraft dominated system. The areas of dissipating squall line thunderstorms may be regions of low CAPE, low humidity, insufficient wind shear, or poor synoptic dynamics (e.g.
A squall line destroyed the front mast of a schooner near Cape Henry. Several boats broke free from their moorings near Salisbury and were subsequently destroyed after passing downstream.
A squall line moved throughout the Southeast and Mid-Atlantic at the beginning of May, bringing more damage due to wind, hail, heavy rain, and flooding across the region.
The Burlington area supercell was the first of what would turn out to be many multi-tornado, long-track supercells, producing additional tornadoes near Roxboro and South Hill, Virginia. Moving rapidly to the east, the squall line entered areas that had experienced sunnier weather earlier in the day, and the squall line began to rapidly fragment into powerful discrete supercells by early afternoon. Explosive wind shear also made the atmosphere extremely prime for tornadic development.
It followed a squall line and a frontal boundary and quickly dissipated. The remnant low produced rain across Northwestern Mexico, it later joined Hurricane Ike and caused damage further inland.
Glossary of Meteorology (2009). Prefrontal squall line. Retrieved on 2008-12-24. Wider rain bands can occur behind cold fronts, which tend to have more stratiform, and less convective, precipitation.
A squall line originating in Illinois produced an F3 tornado in Pickaway County, Ohio, that destroyed several homes and injured six people. The storm was responsible for $4 million in damage.
They requested help by cell phone, but the first Chinook sortie was turned away by an intense squall line, requiring additional flights to drop off and later pick up rescue teams.
Severe squall lines typically bow out due to the formation of a stronger mesoscale high-pressure system (a mesohigh) within the convective area due to strong descending motion behind the squall line, and could come in the form of a downburst. The pressure difference between the mesoscale high and the lower pressures ahead of the squall line cause high winds, which are strongest where the line is most bowed out. Another indication of the presence of severe weather along a squall line is its morphing into a line echo wave pattern, or LEWP. A LEWP is a special configuration in a line of convective storms that indicates the presence of a low-pressure area and the possibility of damaging winds, large hail, and tornadoes.
A squall line (commonly abbreviated SQLN) is a line of thunderstorms, most or all of which have attained severe limits, traveling in an organized fashion. The greatest threats within a SQLN are damaging winds, large hail, and flash flooding, though tornadoes are possible. A derecho is a squall line which is long-lived and consistently produces damaging winds across its entire track. Derechos almost exclusively cause flash flooding and wind damage, which can be very severe.
At approximately 1:00 a.m. CST (0700 UTC), the broken squall line that had affected Oklahoma and Missouri entered the state of Alabama. Individual supercell storms began to develop ahead of the squall line along the Alabama- Mississippi border due to the strengthening of the upper level jet stream. A supercell that developed over Starkville, Mississippi, and tracked over Lamar, Marion and Fayette Counties in Alabama spawned a tornado in Lawrence County, Alabama, at 3:02 a.m.
Numerous reports of damaging winds were associated with the passage of the cold front. Wind gusts from Arkansas to Indiana exceeded 50 mph (80 km/h), bringing down numerous trees and power lines, and causing widespread power outages. A 67 mph (108 km/h) wind gust was recorded during the passage of a squall line at Little Rock National Airport. The highest recorded wind gust associated with the passage of the squall line was 82 mph (131 km/h) in Terre Haute, Indiana.
Early on February 29, in Valley View, Texas, strong straight-line winds accompanied by pea-sized hail damaged the roofs of multiple buildings. That evening, a destructive squall line passed over Chattanooga, Tennessee, toppling sign boards, radio and TV aerials, breaking plate glass windows along Market and Broad Streets, and breaking telephone and power lines. The squall line moved rapidly eastward, passing over Lovell Field at 8:17 pm and capsizing several small aircraft. Winds were measured at around with a peak of .
Prefrontal squall line. Retrieved on 2008-12-24. Rainbands associated with cold fronts can be warped by mountain barriers perpendicular to the front's orientation due to the formation of a low-level barrier jet.
There are several forms of mesoscale meteorology, including simplistic isolated thunderstorms unrelated to advancing cold fronts, to the more complex daytime/nocturnal Mesoscale Convective System (MCS) and Mesoscale Convective Complex (MCC), to squall line thunderstorms.
The storms congealed into a squall line that produced additional severe weather and tornadoes along with flash flooding through Missouri into West Virginia overnight into April 25. Following the squall line, a massive cluster of severe and tornadic thunderstorms with torrential downpours formed over Indiana and Tennessee and trekked eastward, producing massive amounts of damage and numerous casualties. General thunderstorms produced scattered activity during April 26-29 before another outbreak surged through the Great Plains on April 30, the final day of the sequence.
Wind shear is an important aspect of a squall line. In low to medium shear environments, mature thunderstorms will contribute modest amounts of downdrafts, enough to help create a leading edge lifting mechanism – the gust front. In high shear environments created by opposing low level jet winds and synoptic winds, updrafts and consequential downdrafts can be much more intense (common in supercell mesocyclones). The cold air outflow leaves the trailing area of the squall line to the mid-level jet, which aids in downdraft processes.
The boundary between the two formed a squall line stretching from Devon, along the England–Wales border and up across Northern England to the River Tees. Thick clouds, darkened by the Sahara dust, rose to , plunging areas along the squall line into total darkness. In some areas, the lightning continued for 24 hours, and ball lightning was seen at RAF Chivenor in Devon. The dust particles served as seeds for nucleation, causing water to rapidly precipitate out and form especially large raindrops and hailstones.
A summer squall line in Southern Ontario, producing lightning and distant heavy rains. Wind shear is an important aspect to measuring the potential of squall line severity and duration. In low to medium shear environments, mature thunderstorms will contribute modest amounts of downdrafts, enough to turn will aid in create a leading edge lifting mechanism – the gust front. In high shear environments created by opposing low level jet winds and synoptic winds, updrafts and consequential downdrafts can be much more intense (common in supercell mesocyclones).
The cyclone's pre-frontal squall line moved into western Florida between 4:30 and 6:00 p.m. on March 6. Winds gusted to between and across Sarasota and Levy counties. Tides rose to between and above normal.
The main driving force behind squall line creation is attributed to the process of in- filling of multiple thunderstorms and/or a single area of thunderstorms expanding outward within the leading space of an advancing cold front.
Additional significant tornadoes occurred in that area as well. At around the same time, preexisting storms over Indiana and Illinois had begun to consolidate into a somewhat disorganized albeit extensive squall line. As a result of the merging, the threat of tornadoes generally decreased slowly as the storms moved from Indiana into Ohio while the development of a major wind event seemed more apparent, particularly in Ohio. Despite the change in storm mode, additional strong tornadoes still occurred as far east as Western Ohio due to circulations embedded in the squall line.
A wake low is a mesolow The northern end of the squall line is commonly referred to as the cyclonic end, with the southern side rotating anticyclonically. Because of the coriolis force, the northern end may evolve further, creating a "comma shaped" mesolow, or may continue in a squall-like pattern. A wake low is another kind of mesoscale low-pressure area to the rear of a squall line near the back edge of the stratiform rain area.. Due to the subsiding warm air associated with the system's formation, clearing skies are associated with the wake low. Severe weather, in the form of high winds, can be generated by the wake low when the pressure difference between the mesohigh preceding it and the wake low is intense enough.. When the squall line is in the process of decay, heat bursts can be generated near the wake low.
He finished his Ph.D. at Colorado State University (CSU) in Ft. Collins in 1992. At CSU he participated in more field work, including researching squall lines in Australia and his dissertation was titled Observational and Theoretical Study of Squall Line Evolution.
This high- pressure area is formed due to strong descending motion behind the squall line, and could come in the form of a downburst.Peter S. Parke and Norvan J. Larson (2005). Boundary Waters Windstorm. National Weather Service Forecast Office, Duluth, Minnesota.
Numerous other tornadoes and hundreds of damaging wind reports were recorded throughout the afternoon, but the squall line began to weaken late on January 11 as the forcing mechanism lifted northeast into the Ohio River Valley and as daytime heating waned.
A mesoscale convective vortex is a tropical cyclone-like, warm core, a feature which may develop in a squall line, derecho, or MCS. Severe MCVs can become what are essentially small tropical storms or hurricanes, and can in fact become such cyclones, as in the case of Hurricane Barry in July 2019. An MCV will often trail a squall line on its south side. The greatest threats in an MCV are (in the center of circulation and south of the center) extreme winds and (north of the center) flash flooding, in addition to tropical cyclone formation.
'Airfield' zones provide an extra spawn point for players, reducing travel times for players occupying 'Airfield' zones. 'Military Base' zones also routinely bombard enemy zones with rockets, enabling faster capture of enemy zones. When a team has earned a noticeable point advantage, players would be warned in advance of the 'squall line' event, wherein players can no longer respawn upon being shot down. The victor of the game is the team that has accumulated more points in the time limit of the game, or when all enemy players are permanently killed after the arrival of the 'squall line' gameplay event.
At 17:22 UTC on December 31, the National Weather Service St. Louis, Missouri issued a tornado warning for a severe squall line capable of producing rain-wrapped tornadoes and wind damage. The warning covered ten counties in Missouri and Illinois straddling the Mississippi River and included St. Louis. Shortly after the warning's issuance, two EF1 tornadoes tracked across Jefferson and St. Louis counties, causing extensive tree damage and minor property damage. However, the most destructive tornado from the passing squall line touched down at 17:48 UTC east-northeast of Murphy, Missouri in northern Jefferson County.
A squall line produced an long path of straight-line winds in Meigs and McMinn Counties, causing widespread damage. As the squall line passed through Decatur, this violent F4 tornado developed within it over the Decatur Ridge just northeast of Decatur and caused major damage as it moved northeastward through the No Pone Valley. 205 structures were hit by the tornado with three homes and 55 farm buildings being destroyed, including a well built two-story home that was obliterated with debris scattered up to away. A total of 58 other homes and 89 farm buildings were damaged as well.
On 20 July 1929 a wave reported as being between high struck the south coast including busy tourist beaches at Worthing, Brighton, Hastings and Folkestone. Two people drowned and the wave was attributed to a squall line travelling along the English Channel.
Prefrontal squall line. Retrieved on 2008-12-24. and can bring severe thunderstorms, hailstorms, snow squalls, and/or tornadoes. In the spring, these cold fronts can be very strong, and can bring strong winds when the pressure gradient is higher than normal.
In advance of the squall line that was moving rapidly to the east, scattered supercell thunderstorms popped up, and at one point during the nighttime hours, a tornado warning had to be issued for the Dallas–Fort Worth metroplex, a rare occurrence.
The supercells that developed that afternoon ahead of the squall line originated across Louisiana and southern Mississippi. Around 4 p.m. (2200 UTC), a newly-developed supercell produced an EF2 tornado in Marion County, Mississippi. That tornado tracked northeast and entered Lamar County, where it dissipated.
When the convection is strong and linear or curved, the MCS is called a squall line, with the feature placed at the leading edge where the significant wind shifts and pressure rises.Office of the Federal Coordinator for Meteorology.Chapter 2: Definitions. Retrieved on 2006-10-22.
A low precipitation supercell shelf cloud. Shelf cloud forms when a cooler air mass under-flows the warmer moisture laden air. A supercell. While many ordinary thunderstorms (squall line, single-cell, multi-cell) are similar in appearance, supercells are distinguishable by their large-scale rotation.
Yet another severe weather event developed across the Midwest and southern Great Plains on April 19 as another dynamic low pressure system tracked across the area. Thunderstorms began in the late afternoon and early evening with large hail and several tornadoes. Significant damage was reported near Bowling Green, Missouri and Girard, Illinois as a result of tornadoes, the latter of which was rated EF3. Another large tornado was reported near Octavia, Oklahoma before the supercells merged into a very large squall line. Overnight, the squall line tracked eastward with widespread wind damage and many embedded tornadoes across several states, a few as strong as EF2 but most were brief and weak.
During the early morning hours, a cold front with several embedded low pressure areas extended from east Texas northeastward into the Ohio River Valley. An upper-level disturbance that had moved across the frontal boundary the previous evening sparked an area of thunderstorms that morphed into a squall line. This line of severe thunderstorms would produce tornadic activity from the evening on April 26 into the late morning of April 27. Early in the morning the squall line, packing straight-line winds and numerous embedded tornadoes, moved through Louisiana and Mississippi before proceeding to affect North and Central Alabama and parts of Middle and East Tennessee.
The system formed on a warm front that tracked across the Midwest and stretched from the northern Great Lakes to Tennessee. The front was enhanced by a strong jet stream and warm, humid air ahead of it, allowing thunderstorms to develop. A severe thunderstorm watch was issued for the region just west of Evansville as the main threat appeared to be straight-line winds. The system had formed into a squall line but at about 1:30 am CST (0730 UTC), the squall line broke up in the Ohio Valley area, as the low level jet intensified, allowing embedded tornadoes to form rapidly out of newly formed supercells.
The 2006 London tornado was a significant United Kingdom tornado spawned from a squall line moving over the city on 7 December 2006 at approximately 11:02 GMT. Its intensity is estimated to have been T4 on the TORRO scale, equating to F2 on the Fujita scale.
Even weaker and less organized areas of thunderstorms will lead to locally cooler air and higher pressures, and outflow boundaries exist ahead of this type of activity, "SQLN" or "SQUALL LINE", while outflow boundaries are depicted as troughs with a label of "OUTFLOW BOUNDARY" or "OUTFLOW BNDRY".
Late on March 5, a frontal wave moved offshore Galveston, Texas. The system moved along the Gulf coast on March 6. Gale-force winds were confined to behind its prefrontal squall line on March 6. The cyclone moved along the Florida-Georgia border with a central pressure down to .
Another round of severe weather developed late that evening, producing another intense squall line with embedded tornadoes across the northern Gulf Coast region early on March 27, where several tornadoes were reported. Later during the afternoon, various tornadoes developed in North Carolina, causing structural damage in eastern North Carolina.
Cold fronts often follow a warm front or squall line. Very commonly, cold fronts have a warm front ahead but with a perpendicular orientation. In areas where cold fronts catch up to the warm front, the occluded front develops. Occluded fronts have an area of warm air aloft.
Another round of severe weather developed late that evening, producing another intense squall line with embedded tornadoes across the northern Gulf Coast region early on March 27, where several tornadoes were reported. Later during the afternoon, various tornadoes developed in North Carolina, causing structural damage in eastern North Carolina.
The leading area of a squall line is composed primarily of multiple updrafts, or singular regions of an updraft, rising from ground level to the highest extensions of the troposphere, condensing water and building a dark, ominous cloud to one with a noticeable overshooting top and anvil (thanks to synoptic scale winds). Because of the chaotic nature of updrafts and downdrafts, pressure perturbations are important. As thunderstorms fill into a distinct line, strong leading-edge updrafts – occasionally visible to a ground observer in the form of a shelf cloud – may appear as an ominous sign of potential severe weather. Beyond the strong winds because of updraft/downdraft behavior, heavy rain (and hail) is another sign of a squall line.
Hurricane Delta bought strong winds and 14 tornadoes to the Southeastern United States. The most active day was October 10, when numerous tornado warnings were issued in Georgia as a squall line moved through the region. At least six tornadoes were reported. An EF1 tornado injured two people in Covington, Georgia.
These watches were issued through the day, with the first being posted at 7 a.m. CST (1300 UTC) and the last one coming out at 5:35 p.m. CST (2335 UTC). Throughout the afternoon hours, the cold front and the squall line began to stall over portions of Louisiana and Arkansas.
One confirmed EF0 tornado hit the town of Crowley, Louisiana. Another reportedly hit Greene County, Mississippi on March 5. It formed in a squall line, which hit portions of Mississippi, Alabama, and Louisiana. A deadly EF2 tornado struck Rayne, Louisiana early that afternoon, killing a mother while she protected her daughter.
If outflow boundaries or squall lines form over arid regions, a haboob may result. Squall lines are depicted on NWS surface analyses as an alternating pattern of two red dots and a dash labelled SQLN or SQUALL LINE, while outflow boundaries are depicted as troughs with a label of OUTFLOW BOUNDARY.
An EF1 tornado was confirmed in the Bergholz area on June 2. It was part of a severe weather situation from a squall line that moved into Ohio. The tornado damaged some houses and destroyed several trees. Although there were no human fatalities, 2 horses were confirmed killed by flying debris.
Wilfried Jacobs. EUMeTrain: Case Study on Squall Line. Retrieved on 2006-11-19. The strong winds at the surface are usually a reflection of dry air intruding into the line of storms, which when saturated, falls quickly to ground level due to its much higher density before it spreads out downwind.Thinkquest.
A Morning Glory cloud formation between Burketown and Normanton, Australia. The location of the Gulf of Carpentaria. Satellite photo of morning cloud formations over the Gulf of Carpentaria. Northern part of the visible linear cloud is North Australian Squall Line, Morning Glory cloud is the very southern part of this linear cloud.
2 additional tornadoes formed near the Texas coastline from another squall line, rated EF0 near the Chapman Ranch, Texas and EF2 in Refugio, Texas. And 2 more confirmed tornadoes near Woodsboro, Texas an EF0 and near Tynan, Texas an EF1 One more tornado was confirmed near Shin Pond, Maine that damaged many trees.
Overnight, the squall line tracked eastward with widespread wind damage and many embedded tornadoes across several states, a few as strong as EF2 but most were brief and weak. In the early hours of April 20, 2011, a tornado tore through a neighborhood in Oregon, Ohio leaving some significant damage and no injuries.
Darwin occupies one of the most lightning-prone areas in Australia. On 31 January 2002 an early-morning squall line produced over 5,000 cloud-to-ground lightning strikes within a radius of Darwin alone—about three times the amount of lightning that Perth, Western Australia, experiences on average in an entire year.
Once the flow of warm and moist air is cut off from thunderstorms and their associated tornadoes, normally by the thunderstorm's own rain-cooled outflow boundary, the storms begin to dissipate. Rear inflow jets behind squall lines act to erode the broad rain shield behind the squall line, and accelerate its forward motion.
The severe weather phenomenon that affected Kinshasa and its surrounding areas at the time of the accident was a fast moving and severe "Squall Line". The Approach path and Kinshasa airfield were probably covered by inclement weather at the time of the accident. The fast movement of the "Squall Line" can also be visualized by the fact that the weather information provided to the crew at 12:49 by Kinshasa ATC stated of visibility while the weather report (SPECI) at 13:00 reported a visibility of only . The accident occurred at 12:56 So, during the interim period of ten minutes, a rapid change in weather had taken place but the same was not conveyed to the crew by the ATC.
Another low pressure system tracked across the Gulf Coast and Florida on February 12. 21 tornadoes were reported across the region after a squall line broke into bow echo segments. One EF1 and five EF0 tornadoes were confirmed. A woman was killed in Independence, Louisiana when she was picked up and thrown outside a hospital.
Two died and 43 more were injured in Tushka. In Arkansas, strong winds produced by thunderstorms killed at least seven people. Of those deaths, five were confirmed to have been from straight- line winds and two were as a result of a weak tornado embedded in an overnight squall line that tracked across the state.
The depression strengthened throughout the day, and the JMA upgraded it to Tropical Storm Utor later that day. The name Utor was submitted by the United States on behalf of the Marshall Islands, and is a Marshallese word for squall line. Signal no. 3 has been raised in the provinces of Cebu, Leyte, Samar Provinces.
Numerous trees and power lines were downed across both states. One person was injured in Wilson County, Tennessee after a construction crane was blown over onto a car by high winds. Severe storms extended into Ontario, Canada, where a squall line produced some damage. Strong winds downed many trees and power lines, leaving roughly 3,000 people without power.
A sharp cold front triggered an intense squall line that moved into the Pacific Northwest during the late morning hours of April 5, 1972. After moving inland, the storms produced strong winds, large hail, and tornadoes to the region. Weakening of the storms did not take place until late that evening; by then storms had moved over inland.
Windstorms were also reported in Southern Ontario and Southern Quebec which resulted in several injuries and one death, damages and power outages. Other fatalities due to straight-line winds occurred in McComb, Mississippi, early on April 26 and also in Moody, Alabama, Vestavia Hills, Alabama, and Franklin, Tennessee, early on April 27 from the squall line with embedded tornadoes.
The flight remained at until permission was received at 23:06 to descend to 5,000 feet. At 23:08 the crew contacted a company flight that had just departed Omaha. This flight reported moderate to light turbulence. About four minutes later the aircraft entered an updraft within an area of active squall line of severe thunderstorms.
In the mid-afternoon, supercells began to form along a cold front in eastern South Dakota. Additionally, numerous severe thunderstorms formed along the front from Minnesota to Texas. The storms produced multiple weak tornadoes throughout the risk area, none of which exceeded EF1 in intensity. By early evening, the cells merged into a squall line and continued east.
Destroyed mobile home in Arkansas from a tornado that occurred on February 24. A moderate tornado outbreak affected several southern US states. A line of tornado-producing supercells formed out in front of a squall line which produced damaging winds. Over 10 hours, multiple tornadoes touched down and caused $35 million in damage, primarily in Arkansas and Mississippi.
An upper level disturbance across the northern Great Plains interacted with a warm and moist air mass on the afternoon of June 12. This interaction led to the development of supercell thunderstorms across Iowa, Illinois, Wisconsin, and Minnesota. The cells gradually formed into a squall line and turned into a derecho in the Chicago area that evening.
Lack of weather radar also affected the Meteorological Services provided to MONUSCO by PAE. Despite the lack of weather radar, the approaching "Squall Line" should have been observed when it came within visual range of Meteorological Observers on ground and appropriate warning should have been issued via the ATC to all approaching aircraft. The same was not done.
Numerous tornadoes touched down across Texas and Louisiana starting late on December 23 into December 24, associated with the warm sector of a much larger winter storm which produced heavy snow and blizzard conditions farther north. Significant damage was reported in the areas of Longview (where an EF2 tornado touched down), Lufkin (where an EF3 tornado touched down) and Garrison in Texas and in Crowley, Louisiana (tornado rated as EF2 there) where houses were heavily damaged as supercells developed ahead of and within a larger squall line. A moderate risk of severe weather was issued for the afternoon of December 24 across the northern Gulf Coast. Severe activity was limited to the immediate coastal area with supercells embedded within the larger squall line, where a single EF0 tornado was reported.
Wake lows form due to adiabatic warming in the wake of mature squall lines at the back edge of their rain shields, where evaporative cooling is unable to offset warming due to atmospheric subsidence, or downward motion. They can be caused by gravity waves which duct through boundary layers which are deep and cold to the north of a weather front. As with mesoscale high-pressure areas behind a squall line, when new thunderstorm development stops along the squall line, the wake low will weaken as well. Clearing conditions will accompany the wake low, due to the descending warm air mass associated with the feature. Within the United States, these systems have been observed to form in the Mississippi river valley, Southeast,National Weather Service Office Huntsville, Alabama (2009).
The average thunderstorm has a diameter. Depending on the conditions present in the atmosphere, these three stages take an average of 30 minutes to go through. There are four main types of thunderstorms: single-cell, multicell, squall line (also called multicell line) and supercell. Which type forms depends on the instability and relative wind conditions at different layers of the atmosphere ("wind shear").
MCCs commonly develop from the merging of thunderstorms into a squall line which eventually meet the MCC criteria. Furthermore, some MCC formation can be tracked from the plains in Colorado back to the Rocky Mountains. These are called "orogenic" complexes.Wetzel, P.J., W.R. Cotton, and R.L. McAnelly, 1983: A long-lived mesoscale convective complex, Part II: Evolution and structure of the mature complex.
In Cuba, wind gusts reached in the Havana area. A survey conducted by a research team from the Institute of Meteorology of Cuba suggests that the maximum winds could have been as high as . It is the most damaging squall line ever recorded in Cuba. There was widespread and significant damage in Cuba, with damage estimated as intense as F2.
The other fatalities were caused by straight line winds. The squall line continued into the early hours of the morning and caused more severe wind damage and some tornadoes along the East Coast, especially in Georgia and the Carolinas. Numerous power outages also took place due to the extensive wind damage. Nearly 100,000 and 147,000 residences lost power in Tennessee and Georgia respectively.
A shelf cloud such as this one can be a sign that a squall is imminent A squall line is an organized line of thunderstorms. It is classified as a multi-cell cluster, meaning a thunderstorm complex comprising many individual updrafts. They are also called multi-cell lines. Squalls are sometimes associated with hurricanes or other cyclones, but they can also occur independently.
Most commonly, independent squalls occur along front lines, and may contain heavy precipitation, hail, frequent lightning, dangerous straight line winds, and possibly funnel clouds, tornadoes and waterspouts.Weatherquestions.com. What is a Squall Line? Retrieved on 2006-11-19. Squall lines require significant low-level warmth and humidity, a nearby frontal zone, and vertical wind shear from an angle behind the frontal boundary.
Another supercell thunderstorm also produced two EF3 wedge tornadoes that passed near Fellsburg and Hudson, causing significant damage. Around 10:00 p.m. CDT (0300 UTC), a broken squall line began to form across the eastern portions of the Texas and Oklahoma panhandles; a thunderstorm developed ahead of the northern line segment in northwestern Wheeler County, Texas at approximately 10:30 p.m.
A destructive QLCS tornado occurred in Tulang Bawang regency, killing two people and leaving six others injured. Several houses were destroyed or collapsed and many trees were downed. A total of 66 homes were badly damaged or destroyed and 179 others sustained minor damage. The tornado itself was spawned along the leading edge of a squall line of severe thunderstorms that was moving through the area.
CDT (0130 UTC), a squall line began developing over south-central Nebraska and central Kansas. Several corridors of intense winds, possibly associated with brief tornadoes, were observed in Clay and Washington counties in Kansas. Several homes were damaged or destroyed by the winds. Near Milford Lake, a non-tornadic gust of was measured; two people were injured near the lake after their camper tipped over.
The most intense cell tracked from Dallas County to Story County, producing three brief tornadoes and straight-line winds along its path. The touchdowns in Iowa marked the end of a record 358-day span with no tornadoes in the state. Severe activity began decreasing by 10:00 p.m. CDT (0300 UTC) as the main squall line over Missouri entered an area of increased capping.
However, as the weakening squall line encountered higher instability and more favorable upper-level winds, the line split into several supercells in a process still not fully understood; these storms produced several tornadoes in central Kentucky, eastern Tennessee, southwestern Virginia, and northwestern North Carolina. While no longer producing severe weather itself, the MCV continued to enhance thunderstorms early the next morning across southeastern Virginia.
By 3:00 am CST on February 29, Branson, Missouri was reporting injuries and severe damage to the town from an EF2 tornado, with homes destroyed and several hotels, businesses, and theaters sustaining severe damage. Three other deaths occurred in southern Missouri. As the storms moved into Illinois in the pre-dawn hours, they merged into an intense squall line with embedded semi-discrete supercell thunderstorms.
In 1993, the Storm of the Century brought an intense squall line, and winds gusting over , to much of the Sunshine State during the early morning hours of March 13. Later that day, flurries were witnessed across the Florida Panhandle in its wake. A frontal wave which became a powerful Christmas 1994 Nor'easter moved across Florida, bringing windy and rainy conditions to the state.
Following the widespread power outages from a severe ice storm, an additional 161,588 residences lost power due to winds. Flooding and high winds in Michigan knocked out power to about 57,000 residences. In southern Michigan, upwards of of rain fell, leading to faster snowmelt. In Tennessee, several structures were damaged and numerous trees were knocked down, closing roads throughout the state as the squall line tracked eastward.
Weak mid-level winds were expected to mitigate the tornado risk, owing to a severe thunderstorm watch across central Kansas down into central Oklahoma. At 10:28 p.m. CDT, however, a narrow but significant EF3 tornado embedded in the squall line moved through southern sections of El Reno, Oklahoma, causing severe damage, killing two people and injuring 29 others. A total of 17 tornadoes were confirmed.
Five people lost their lives. The system gradually moved east on March 29, but the squall line left over from events the previous night prevented a major outbreak. Even so, three tornadoes were reported in Oklahoma, two in the Oklahoma City metropolitan area, which injured several people. The SPC had issued a moderate risk again for March 30 and March 31 over portions of southern Texas.
Early that evening, supercells containing severe thunderstorms and tornadoes was developed along a nearly continuous line from near Lubbock, Texas to Rapid City, South Dakota. Before the supercells reformed into a squall line late that evening, at least 63 tornadoes were reported, many of which were very large and potentially destructive. Fortunately, the area is sparsely populated, preventing widespread death and destruction. Still, five people were killed.
The leading area of a squall line is composed primarily of multiple updrafts, or singular regions of an updraft, rising from ground level to the highest extensions of the troposphere, condensing water and building a dark, ominous cloud to one with a noticeable overshooting top and anvil (thanks to synoptic scale winds). Because of the chaotic nature of updrafts and downdrafts, pressure perturbations are important.
EF2 tornado in Chicot County, Arkansas In the overnight hours, a strong squall line/serial derecho formed across the Central United States. Widespread tree and building damage was reported across the Kansas City metropolitan area. Winds as strong as 85 mph (136 km/h) were reported, and many power outages took place, impacting about 50,000 customers. About 200 buildings were destroyed and many others damaged.
While many of these tornadoes were weak, some were large and wedge-shaped and reached EF2 intensity. One of these strong tornadoes killed one person and caused damage in the town of Durant, Mississippi. On May 1, another squall line of severe storms developed further to the north. The Storm Prediction Center ended up issuing a tornado watch for parts of Pennsylvania and New York.
Starting in 1976, residents began receiving mysterious letters from an unknown source. The identity of the letter writer remains a mystery to this day. On October 13, 1999, an F-3 tornado hit the city, set off by a squall line moving through the region. The tornado touched down on the north side of town, doing substantial damage to a barber's shop and a masonry building.
During the morning of May 21, a strong shortwave trough over the Texas Panhandle moved eastward into Oklahoma. Moderate instability in the region led to the formation of thunderstorms across the state, with strong thunderstorms developing near the Oklahoma City metropolitan area, including the devastated city of Moore. Ahead of the main line of storms, a loosely organized squall line formed over central Tennessee by 11:15 a.m. CDT (1615 UTC).
In Arkansas, high winds produced by the squall line knocked out power to 315,324 residences and caused widespread structural damage. Trees and power lines were brought down in eight counties, and several homes in Independence and Van Buren County sustained damage. The damage in these counties was caused by winds gusting up to and leaving $200,000 in damages. An wind gust in Van Buren blew a barn onto Arkansas Highway 9.
West Texas Mesonet Observations of Wake Lows and Heat Bursts Across Northwest Texas. American Meteorological Society. Retrieved on 2009-04-24. Severe weather, in the form of high winds, can be generated by the wake low when the pressure difference between the mesohigh preceding it and the wake low is intense enough.. When the squall line is in the process of decay, heat bursts can be generated near the wake low.
After a few hours, these supercell thunderstorms lessened in strength as they neared the Greater St. Louis metropolitan area. While the cluster of thunderstorms was tracking through Missouri, a new squall line with embedded supercells developed across eastern Oklahoma and Kansas, demarcating a dry line boundary. Although linear storm systems tend to indicate strong wind events and not tornadoes, these storms tracked eastward into southwestern Missouri and eventually produced several tornadoes.
Late on June 3, 2009, a cold-core non-tropical low pressure area located over the Baltic Sea collided with a warm air mass, creating atmospheric instability. The result was a line of severe thunderstorms, also known as a squall line, in the Moscow area. One of the thunderstorms broke off and developed into a supercell thunderstorm about from Moscow, Russia. The supercell spawned a wide tornado in Krasnozavodsk.
Areas south and east of the squall line saw less severe storms, but the rain that fell in the night of 1–2 July 1968 was rich in Saharan dust, turning it blood red and leaving dusty deposits on the surfaces it fell on – only the south coast and uplands of Wales avoided the red rain. The last comparable storm associated with Saharan dust was seen in October 1755.
Significant damage was reported near Scotland, including many vehicles thrown off the road and many homes and other buildings being destroyed. The supercell that spawned the Scotland area tornado also produced a damaging EF2 near Mt. Olive as well. On April 11, a supercell ahead of the squall line developed in eastern Mississippi. A large wedge tornado touched down in Kemper County and moved into Noxubee County and Pickens County, Alabama.
Tides up to in Virginia resulted in some beach erosion and coastal flooding due to the prolonged duration of the event. Although no warnings were issued, boaters in Newfoundland were advised to closely monitor the storm. In Hampton, Virginia, a funnel cloud spawned by a squall line associated with Amy formed just offshore. As a tropical depression, Amy produced scattered rainfall in Florida, peaking around near the Georgia border.
A special, and much rarer, kind of downburst is a heat burst, which results from precipitation-evaporated air compressionally heating as it descends from very high altitude, usually on the backside of a dying squall line or outflow boundary. Heat bursts are chiefly a nocturnal occurrence, can produce winds over , are characterized by exceptionally dry air, can suddenly raise the surface temperature to or more, and sometimes persist for several hours.
In Deep East Texas, a series of supercell thunderstorms developed ahead of a squall line. As thunderstorms approached the area, a Severe thunderstorm warning was issued at 1:27 a.m. CST for northern Caddo and Bossier Parishes. The supercell which spawned the tornado tracked over the town of Deadwood, Texas, before moving over Southwood High School, Pierremont Mall, and the VA Hospital in Shreveport with no reports of tornadic activity.
Behind the low pressure area was much cooler and drier air. The clash of these two differing air masses was the impetus for the development of the severe weather. A squall line moving at speeds to with embedded supercells entered Minnesota from the southwest during the early afternoon hours, and raced northward across most of the state. The primary threat from these storm was large hail, which was enhanced by the strong downburst winds.
Discrete supercells soon developed within the warm sector across Louisiana, while a line of thunderstorms congealed along the encroaching cold front. Numerous tornadoes, some strong to intense, were observed across Louisiana and Mississippi throughout the afternoon hours. By late evening, isolated supercells were overtaken by the squall line, reducing the significant tornado threat. The following morning, the storms propagated eastward into Georgia, where a few additional tornadoes occurred before the outbreak came to an end.
Showers come from individual clouds as well as from groups of these. In mid- latitude regions, showers are often associated with cold fronts, often found along and behind it. However they can be in-bedded into a continuous rain episode when there is presence of band of conditional symmetric instability in an otherwise stable air mass. They can also be part of large convection zones called mesoscale convective system such as a squall line.
A large exposed area makes airships susceptible to gusts and difficult to takeoff, land, or moor in windy conditions. Propelling airships with cyclorotors could enable flight in more severe atmospheric conditions by compensating for gusts with rapid thrust vectoring. Following this idea, the US Navy seriously considered fitting of six primitive Kirsten-Boeing cyclorotors to the airship. The Shenandoah crashed while transiting a squall line on 3 September 1925 before any possible installation and testing.
The music video for "Vanilla Twilight" premiered on March 22, 2010. The video uses the album version of the song and features a cameo appearance by Shaquille O'Neal. The video was directed by Steve Hoover and was filmed on location in Pittsburgh, Pennsylvania, and at the Marblehead Lighthouse in Ohio. The video shows various people and a dog witness in awe, staring at a swirling mammatus cloud formation associated with a squall line.
Atmospheric moisture was also atypically high during this period, with precipitable water content persisting between , thereby increasing the precipitation potential of each individual shower and thunderstorm. The first rains associated with the flood occurred on May 18, when a squall line moved across eastern Oklahoma and western Arkansas. Additional showers immediately preceding and succeeding the squall enhanced rainfall totals. Between May 20–21, another storm system moved from the Rocky Mountains into Oklahoma.
H. Desert Research Institute. Retrieved on 2006-10-22. Well behind mature squall lines, a wake low can develop on the back edge of the rain shield, which can lead to a heat burst due to the warming up of the descending air mass which is no longer being rain-cooled. Smaller cumulus or stratocumulus clouds, along with cirrus, and, sometimes, altocumulus or cirrocumulus, can be found ahead of the squall line.
The storms that bought the tornadoes on April 4 also bought a large squall line across Alabama. This proved disastrous when Southern Airways Flight 242 attempted to fly around the storm and instead flew straight into it. Massive amounts of very large hail and very heavy rain battered the plane and destroyed its engines. With no way to keep flying, it attempted a landing on a stretch of highway in New Hope, Georgia.
An area of convection developed across eastern Iowa near a weak stationary/warm front and ultimately matured, taking on the shape of a wavy squall line across western Ohio and southern Indiana. The system re-intensified after leaving the Ohio Valley, starting to form a large hook, with occasional hook echoes appearing along its eastern side. A surface low pressure center formed and became more impressive later in the day.David M. Roth.
The severe threat shifted towards damaging straight-line winds on May 21 as a large squall line developed across the southern states. Further north in Ontario, three tornadoes, including an EF2, touched down. Over the following five days, the system responsible for the outbreak moved very little across the Eastern United States. By May 24, it virtually stalled off the coast of New England, resulting in several days of heavy rain across the region.
Tropical storm-force wind gusts affected several counties across southern Florida, particularly Collier, Miami-Dade, and Monroe counties. A gust of was observed at the Turkey Point Nuclear Generating Station. Farther south, a strong squall line moved through Key West, damaging streetlights and generating a wind gust at the National Weather Service's Key West office. On August 25, a St. George Island first responder drowned while trying to rescue a swimmer caught in rough surf.
Where treefall gaps are usually formed by falling trees or branches due to old age or disease, large-scale blow-downs are caused by squall lines, which generate heavy rain and strong winds.Negrón‐Juárez, R. I., Chambers, J. Q., Guimaraes, G., Zeng, H., Raupp, C. F. M., Marra, D. M., Ribeiro, G. H. P. M., et al.(2010). Widespread Amazon forest tree mortality from a single cross‐basin squall line event. Geophysical Research Letters.
Supercells are usually found isolated from other thunderstorms, although they can sometimes be embedded in a squall line. Typically, supercells are found in the warm sector of a low pressure system propagating generally in a north easterly direction in line with the cold front of the low pressure system. Because they can last for hours, they are known as quasi-steady-state storms. Supercells have the capability to deviate from the mean wind.
The squall line and associated convection resulted in significant flooding south of St. Louis, Missouri and in eastern Kentucky. Prior to becoming a mesocyclone, the system produced upwards of of rain over parts of Kansas during the morning hours. In Rice County, high waters washed out several small bridges and low water crossings and damaged concrete structures, leaving roughly $340,000 in losses. In some places, rainfall reached within a 30-minute span, leading to widespread street flooding.
A mesohigh forms underneath the downdraft in a squall line and is associated with the cold pool of a thunderstorm. It is largely formed by hydrostatic phenomenon, specifically the evaporation of falling precipitation. As precipitation, primarily rain, falls in the downdraft, it evaporates in the unsaturated air, leading to cooling in the downdraft due to an absorption of latent heat. The cooling of the air leads to an increase in the pressure as the air becomes denser.
On March 29, the squall line that moved eastward prevented a major outbreak during the daytime hours. Only a slight risk of severe storms was issued that day. Nonetheless, several tornadoes were reported, with two striking the Oklahoma City metropolitan area with almost no advance warnings issued before they struck. Significant damage was reported there with at least two people hospitalized when their RV was hit and four others injured during a tornado ten minutes later.
Wyndham recorded while Kalumburu recorded of rainfall. In the early hours of 21 February the system returned to the open waters of the Indian Ocean, causing it to redevelop back into a cyclone. The system was located northwest of Broome. The cyclone continued to track southwest at a relatively fast pace and produced a squall line that generated four tornadoes in the mining town of Karratha which damaged 38 homes as well as numerous cars, buildings and a school.
A low pressure system tracked across the Southern United States on March 6 and 7. It produced several tornadoes along the immediate Gulf Coast, including an EF1 in Corpus Christi, Texas on March 6. In the overnight and early morning of March 7, a squall line tracked across the Gulf of Mexico and into Northern Florida, with supercells forming within it. Other tornadoes took place near Lake City where two people were killed and about 50 homes were damaged.
At 7:58 p.m. CDT, the first tornado watch was issued across the Ark-La-Tex region; several more watches were introduced over subsequent hours. A pair of long-tracked supercells developed across Tarrant and Johnson counties, intersecting a very unstable regime and producing significant tornadoes as a result. A squall line formed along the cold front farther west, producing a wide swath of damaging winds and additional tornadoes as it tracked across the South-Central United States.
The most significant side project was Squall Line. It also featured members of other local bands and former and present Infected members. Andyboy was also in Kill Toby Wyatt which featured members from Deep 13 and The Parlor Boys and is now playing drums with local stoner rockers Stampede and playing guitar in Hateshrines with former Infected and Deep 13 bandmate Mark Borders. Andy has now started a stoner/emo band called Horned Owl as well.
In Rolla, Missouri, at least four people were killed and several others were injured. It is the deadliest December tornado outbreak in the US since December 16, 2000 and they were the first killer US tornadoes since September 16. Numerous tornadoes also touched down in the St. Louis metropolitan area which were embedded in a squall line, including reports in the city of St. Louis itself. The most significant damage was in Sunset Hills and injuries were reported there.
An EF2 tornado near Portland, Arkansas also caused heavy damage. During the mid-morning hours, an EF2 tornado embedded in the squall line struck Meridian, Mississippi, causing significant damage to homes and apartment buildings. On April 15, an enhanced risk of severe weather was issued for parts of Virginia and the Carolinas, again including a 10% risk of tornadoes. Semi-discrete supercell structures embedded in the line produced strong tornadoes in North Carolina, South Carolina, and Virginia.
The squall line continued to push eastward into the Mid-Atlantic states on February 21, leading to numerous damaging wind reports and several tornadoes from Georgia to Maryland. A brief but strong EF2 clipped the northeast side of Fort Payne, Alabama, causing significant damage to a factory, an apartment complex, and some homes. Another EF2 struck Dublin, Georgia, and destroyed one home, damaged 59 others, and downed numerous trees. Overall, this moderate outbreak produced 46 tornadoes and no fatalities.
A High Risk had never before been issued for the Northeastern United States, and hasn't been since this event. This indicated an abnormally dangerous weather situation for this region of the country, a situation more common in the Plains States and Midwest. Around 1 pm, the Michigan derecho was moving into New York from Ontario and rapidly weakening. The decaying squall line broke apart into discrete convection over New York and Pennsylvania, which quickly re-intensified into tornadic supercells.
Ahead of the main cold front, a separate storm formed into a supercell southwest of Williamsford in Grey County, likely triggered by the aging squall line further west. Then, at about 5:50pm, a funnel cloud touched down about southwest of Williamsford. Only sporadic tree damage took place at this point. The storm was high-based, and there was a large gap between the tornado and the core of the storm which was consistent through much of the tornado's life.
The pampero is a burst of cold polar air from the west, southwest or south on the pampas in the south of Brazil, Argentina, Uruguay, Paraguay and Bolivia. This wind (often violently) picks up during the passage of a cold front of an active low passing by. It takes the form of a squall line and there is a marked drop in temperature after its passing. The Pampero is most common at winter in the southern hemisphere (principally between May and August).
When he arrived at the University of Washington in 1972, Houze began developing what became known as his Mesoscale Group. With this group, he conducted research for over 46 years. In the early years, he participated in the Global Atmospheric Research Programme’s Atlantic Tropical Experiment (GATE)—the largest field campaign ever to study weather. In GATE, he was on board a ship instrumented with radar, and was one of the first to use radar to document a tropical squall line.
This squall line continued to renew its energy as it passed through the Midwest, Pennsylvania, New Jersey, New York, and New England, causing wind and water damage, and dumping of snow in central and eastern Massachusetts. The resulting power outages affected homes throughout the northeastern seaboard. The most destructive of the weather events, a long- track EF4 tornado, traveled for nearly an hour through four counties in Oklahoma during the evening of February 10\. It destroyed 114 residences in Lone Grove alone.
In cooler regions of North India, immense pre-monsoon squall-line thunderstorms, known locally as "Nor'westers", commonly drop large hailstones. In Himachal Pradesh, Summer lasts from mid April till the end of June and most parts become very hot (except in alpine zone which experience mild summer) with the average temperature ranging from to . Winter lasts from late November till mid March. Snowfall is generally common in alpine tracts that are above , especially those in the higher- and trans-Himalayan regions.
The entire 40-hour event from the evening of Monday, May 8, through the morning of Wednesday, May 10, consisted of two distinct heavy rainfalls. By Wednesday morning, storm total rainfall amounts of were common across portions of southeast Louisiana and south Mississippi. A cold front approached the region from the west, preceded by a squall line. The airmass that entered western Louisiana on May 8 exhibited considerably lower dewpoints than the tropical airmass across east Louisiana and southeast Mississippi.
Pressure perturbations around thunderstorms are noteworthy. With buoyancy rapid within the lower and mid-levels of a mature thunderstorm, updraft and downdraft create distinct mesocenters of pressure. As thunderstorms organized in squall lines, the northern end of the squall line is commonly referred to as the cyclonic end, with the southern side rotating anticyclonically (in Northern hemisphere). Because of the coriolis force, the northern end may evolve further, creating a "comma shaped" wake low, or may continue in a squall-like pattern.
The weather changed suddenly as the squall line approached, with a strong northeast wind developing against an outgoing tide. The wind has been estimated at and the waves as high as in the rip tides near Montauk Point. While rounding Montauk Point at approximately 2:00 PM, Pelican was hit by two successive waves on the starboard quarter and capsized to port, spilling most of her passengers and crew into the water while trapping others inside the cabin. The vessel then foundered.
Because of this, more than one million customers were without power and had no warning of any approaching tornadoes later that day. From the late morning to the early afternoon, another squall line moved through northern parts of Mississippi and Alabama as high wind shear and low-level moisture persisted. However, this time several discrete supercells developed along and in front of the line, spawning seven weak tornadoes across Morgan, Limestone, and Madison Counties in northern Alabama around noon that day.
A severe weather event developed across the Midwest and southern Great Plains on April 19 as a dynamic low pressure system tracked across the area. Thunderstorms began in the late afternoon and early evening with large hail and several tornadoes. Significant damage was reported near Bowling Green, Missouri and Girard, Illinois as a result of tornadoes, the latter of which was rated EF3. Another large tornado was reported near Octavia, Oklahoma before the supercells merged into a very large squall line.
Ahead of the developing low pressure area, a squall line of thunderstorms developed along a low-level jet stream. The line was first noted around 3:35 am CDT in Cass County, Iowa where winds were recorded at the Atlantic Municipal Airport. Later that day, a much stronger line of severe thunderstorms developed in Plymouth County. Wind gusts up to were recorded in the county, two barns and a horse shed were shifted off their foundation and several trees were uprooted.
As the storms moved into Illinois in the pre-dawn hours, they merged into an intense squall line with embedded semi-discrete supercell thunderstorms. A violent EF4 tornado touched down and ripped through the city of Harrisburg, destroying entire neighborhoods, flattening businesses, and killing 8 people before causing additional destruction in the neighboring town of Ridgway. After sunrise, additional supercells developed and produced numerous tornadoes across Kentucky and Tennessee. Two tornadoes, rated EF1 and EF2, caused significant damage in Greenville, Kentucky.
A widespread and deadly tornado outbreak affected the Southeastern United States on Easter Sunday and Monday, April 12–13, 2020. Several tornadoes were responsible for prompting tornado emergencies, including the first one to be issued by the National Weather Service in Charleston, South Carolina. A large squall line formed and tracked through the mid-Atlantic on April 13, prompting more tornado warnings and watches. A total of 15 watches were produced during the course of the event, two of which were designated Particularly Dangerous Situations.
High-end EF2 damage to a house near Carrollton, Alabama. On January 10, the Storm Prediction Center issued a moderate risk of severe weather for much of the Southern United States, including a 15% hatched risk of tornadoes. A squall line of severe thunderstorms with numerous embedded circulations and semi-discrete supercell structures moved from Texas and Oklahoma to the East Coast, producing numerous tornadoes. A high-end EF2 tornado near Carrollton, Alabama destroyed multiple homes and mobile homes, and resulted in three fatalities.
The most dramatic events unfolded on May 20 as a large EF5 tornado devastated parts of Moore, Oklahoma, killing 24 people. Thousands of structures were destroyed, with many being completely flattened. Several other tornadoes occurred during the day in areas further eastward, though the majority were weak and caused little damage. The severe threat shifted towards damaging straight-line winds on May 21 as a large squall line developed across the southern states. Further north in Ontario, three tornadoes, including an EF2, touched down.
The squall line continued to produce damaging winds as it progressed eastward into Illinois and Indiana. Three additional tornadoes touched down into the early hours of May 21, including a brief EF2 in Mount Olive, Illinois around 10:14 p.m. CDT (0314 UTC). Throughout the day, the SPC received a total of 447 reports of severe weather: 37 for tornadoes, 281 for wind, and 129 for hail; however, some of the wind and hail reports were associated with a separate system over the Southeastern United States.
The National Weather Service tracked a very turbulent squall line of thunderstorms moving northeasterly across Portland, Oregon, the strongest of which was near the city of Tigard. The tornado formed from this storm and touched down near the edge of the Columbia River, moving 1½ miles before crossing the river. The tornado was difficult to observe because of the fog and the mud and flying debris drawn up by the tornado. After making landfall on the Washington side of the river, it continued its journey before dissipating.
The fast moving cold front pushed a storm through the city rather quickly, dumping 0.81 inches of rainfall in a relatively short time. But what accompanied the squall line of severe thunderstorms was the deadliest tornado in Nashville's history. By the early evening, while the air was still warm and humid, destruction began four miles west of downtown over the rim of hills, near Charlotte Pike and Fifty-first Avenue. The damage between this point and downtown was not great, but the tornado quickly intensified.
The crew of the sunken vessel noted the wind suddenly shifted and increased velocity from to . A National Hurricane Center satellite specialist, James Lushine, stated "during very unstable weather conditions the downburst of cold air from aloft can hit the surface like a bomb, exploding outward like a giant squall line of wind and water." A similar event occurred to Concordia in 2010, off the coast of Brazil. Scientists are currently investigating whether "hexagonal" clouds may be the source of these up-to- "air bombs".
In the morning, they issued a forecast for "heavy thunderstorms" effective for 5–6 pm that evening. This would allow the base's commander to alert base personnel that they may institute their brand-new tornado precautions. As the day wore on, conditions appeared more and more favorable for thunderstorms, and more and more similar to the events of March 20. Weather radar images showed a severe squall line had formed to the west, and weather stations to the west reported cumulonimbus clouds and thunderstorms.
Individual cells might move downstream but additional cells forming upwind of the cluster can move directly over the path of the previous cell, forming training echoes. A multicellular storm can sometimes develop into a Mesoscale Convective System (MCS) or be a squall line. Updrafts reform new cells continually at the leading edge of system with rain and hail following behind. Individual thunderstorm updrafts and downdrafts along the line can become strong, producing large hail and strong outflow of straight-line winds ahead of system.
Thunderstorms may line up in a series or become a rainband, known as a squall line. Strong or severe thunderstorms include some of the most dangerous weather phenomena, including large hail, strong winds, and tornadoes. Some of the most persistent severe thunderstorms, known as supercells, rotate as do cyclones. While most thunderstorms move with the mean wind flow through the layer of the troposphere that they occupy, vertical wind shear sometimes causes a deviation in their course at a right angle to the wind shear direction.
As the aforementioned, well-defined shortwave trough progressed eastward into the lower Mississippi Valley, a mesoscale convective vortex organized over west-central Mississippi. Embedded circulations and semi-discrete supercell structures within this complex led to 44 confirmed tornadoes, the strongest of which caused high-end EF2 damage in Morton, Mississippi. This ties the Hurricane Rita tornado outbreak as the largest outbreak in Mississippi state history. As the squall line tracked east, numerous reports of damaging wind gusts were received across the Southeast United States.
When the convection is strong linear or curved, the MCS is called a squall line, with the feature placed at the leading edge of the significant wind shift and pressure rise. This feature is commonly depicted in the warm season across the United States on surface analyses, as they lie within sharp surface troughs. If squall lines form over arid regions, a duststorm known as a haboob may result from the high winds in their wake picking up dust from the desert floor.Western Region Climate Center (2002).
When cirrus clouds precede a cold front, squall line or multicellular thunderstorm, it is because they are blown off the anvil, and the next to arrive are the cumulonimbus clouds. Kelvin-Helmholtz waves indicate extreme wind shear at high levels. Within the tropics, 36 hours prior to the center passage of a tropical cyclone, a veil of white cirrus clouds approaches from the direction of the cyclone. In the mid to late 19th century, forecasters used these cirrus veils to predict the arrival of hurricanes.
Blizzard warnings were issued for areas around Denver due to the strong winds accompanying the system along with snowfall. Parts of Interstate 80 were shut down due to the extreme winter weather conditions. Ahead of its cold front, thunderstorms began to fire up, prompting the National Weather Service to issue a tornado watch. A squall line later developed out of this as more storms began to fire up and move eastwards, with the severe weather threat shifting more to the east towards the East Coast.
As the system pushed eastward across Missouri and Arkansas, and as a warm front drifted northward, severe thunderstorms broke out along both boundaries. Several storms in association with a squall line caused damaging winds. That evening, a damaging EF2 tornado touched down in the St. Louis suburb of Hazelwood, Missouri, tearing the roofs off of several homes and apartment buildings, downing numerous trees and power lines, and flipping many cars. Another EF2 tornado touched down in Van Buren County, Arkansas, prompting a tornado emergency.
Classic derechos occur with squall lines that contain bow- or spearhead-shaped features as seen by weather radar that are known as bow echoes or spearhead echoes. Squall lines typically "bow out" due to the formation of a mesoscale high pressure system which forms within the stratiform rain area behind the initial convective line. This high pressure area is formed due to strong descending air currents behind the squall line, and could come in the form of a downburst.Parke, Peter S. and Norvan J. Larson (2005).
During the early morning hours of July 10, a brief but strong tornado struck the Prairie View RV Park on the south side of Watford City, North Dakota. The tornado was embedded in a squall line that was moving through the area, and destroyed numerous RVs, trailers, manufactured homes, and other structures along its short path. The tornado killed one newborn baby and resulted in 28 other injuries, 9 of which were critical. In addition, a weak tornado briefly touched down near Pennsuco, Florida, causing no damage.
Low pressure records for March were set in areas of twelve states along the Eastern Seaboard, with all-time low pressure records set between Tallahassee and Washington, D.C. Snow began to spread over the eastern United States, and a large squall line moved from the Gulf of Mexico into Florida and Cuba. The storm system tracked up the East Coast during Saturday and into Canada by early Monday morning. In the storm's wake, unseasonably cold temperatures were recorded over the next day or two in the Southeast.
A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. For this reason, these storms are sometimes referred to as rotating thunderstorms.ON THE MESOCYCLONE "DRY INTRUSION" AND TORNADOGENESIS, Archived at: , Leslie R. Lemon Of the four classifications of thunderstorms (supercell, squall line, multi-cell, and single-cell), supercells are the overall least common and have the potential to be the most severe. Supercells are often isolated from other thunderstorms, and can dominate the local weather up to away.
Meanwhile, icy conditions continued in much of the Central United States. By late on January 14, a surface low developed east of the upper-low as it moved swiftly towards the United States–Mexico border. The surface low, while intensifying, as a result of interaction with the incoming moisture, developed a squall line of thunderstorms along its cold front, as it and the upper-low emerged into the Southwestern United States. The entire storm system continued to push northeastwards through the state of Texas on January 15.
A squall line affected the central Florida peninsula on April 4, and both tornadoes originated as waterspouts over the Gulf of Mexico. The two tornadoes were spawned from a single thunderstorm that entered the Tampa Bay region, and they are believed to have represented a tornado family. Initially, the tornadoes were poorly forecasted by the U.S. Weather Bureau, since meteorological analysis did not indicate the presence of an adjacent surface low, which would have enhance conditions for tornadoes. The first Tornado Watch was not released for the central Florida area prior to the tornadoes.
During the morning hours of February 10, a squall line developed along a cold front that stretched from western Arkansas, down through northwest Louisiana, and into east Texas. Simultaneously, a warm front was ascending northward through Mississippi and Louisiana. The area between the fronts became increasingly unstable as the day went on, and four tornado watches were issued across Texas, Louisiana, Mississippi, and Alabama throughout the day as the storms tracked eastward. The watches were issued as very strong wind shear and instability engrossed the area, causing the development of supercell thunderstorms.
The tornado outbreak of December 16–17, 2019 was a significant severe weather event that affected the Southern United States. Discrete supercells developed in the early morning on December 16 and moved northeast, spawning multiple strong, long-tracked tornadoes in cities such as Alexandria and in Laurel before congealing into an eastward-moving squall line. During the outbreak, the National Weather Service issued several PDS tornado warnings as well as a rare tornado emergency for Alexandria. In addition to this, the Storm Prediction Center issued six tornado watches for the outbreak.
Activity was expected to become associated with a squall line by the evening as the cold front moved slowly eastward. In light of that, the SPC issued a moderate risk of severe thunderstorms for south-central Oklahoma, eastern Kansas, western Missouri, and extreme southeastern Nebraska. By the afternoon hours, rapid destabilization of the boundary layer began across eastern Kansas, prompting a tornado watch for the area. Further south in Oklahoma, a rapidly mixing dry line accompanied by a deepening surface low moved eastward into an area with deep moisture.
Many experts and NWS meteorologists considered this to be one of the worst derechos and MCVs in the past decade. The Storm Prediction Center issued two "particularly dangerous situation" severe thunderstorm watches and a vividly worded tornado watch, mentioning the possibility of winds in excess of . Local National Weather Service offices in Springfield, Missouri, and Paducah, Kentucky, also issued strongly worded severe thunderstorm warnings, with precautionary statements similar to those used in tornado warnings. As both the initial squall line and MCV weakened, very little severe weather was reported between southern Illinois and central Kentucky.
Damage to a business in downtown Doniphan, Missouri on May 8, 2009 The initial squall line formed in central Kansas, to the northwest of Hutchinson. In Hutchinson, several airplanes were flipped at a local airport, and 21,000 people were left without power. A woman was killed in New Albany, Kansas, when her mobile home was blown forty feet off of its foundation. National Weather Service survey teams found that winds reached in the area, which also resulted in the destruction of a church and the town's post office, in addition to damaging several homes.
Nat formed from an area of thunderstorms which formed along a trough trailing from Melissa. First noted on September 14, the system developed into a tropical depression and tropical storm on September 15. At this point in its life cycle it approached Guam from the west, when a squall line moved across the island, bringing wind gusts to . One person drowned when knocked into the ocean, while 24 were injured, most of which due to a lightning strike which occurred in the wake of Nat along its trailing surface trough.
However, service was suspended in 1951 when the airline upgraded to twin- engine aircraft that could not use the short runways. On 6 August 1952, the Sherman City Council approved a bond issue to extend the runways, with the expectation of an additional CAA grant to help fund the project. The grant funds did not materialize, but in May 1953, the city contributed additional funding to complete the project so that Central could resume service. On 14 December 1971, high winds from a squall line destroyed one hangar at the airport and severely damaged another.
However, the storm began to lessen in intensity and become larger, forming a multi-squall line as it moved further south. A second wave of storm activity developed behind the first set, delivering further falls to northern Perth. Around 4.30pm, a severe thunderstorm warning was issued for Mandurah and surrounding areas. However, the storm had begun to move further inland, resulting in no hail reported in Mandurah or Rockingham and 17.4/13.4 mm at Garden Island and Mandurah respectively while inland towns such as Dwellingup and Waroona received 30.2 and 26.8mm respectively.
The storm system responsible for the tornado outbreak resulted from the unusual congruence of a cold, dry system, originating in the Four Corners and a warm, moist system, moving north out of Texas. Complicating factors included daytime heating and a strong wind field favorable to the creation of circulating thunderstorms. On the second day, the stronger cold front limited discrete supercell activity and the risk of tornadoes decreased significantly. A squall line, however, produced high winds and rain along the river valleys, primarily those of the Mississippi and Ohio Rivers.
Once the supercell was overtaken by the squall line, it slowed considerably, and the torrential rains caused flash flooding and at least 13 fatalities. Most of the drownings occurred while attempting to cross flooded roads. Some children died while playing around drainage culverts, and two people died when a roof overloaded with rainwater collapsed. The combination of the heavy rain and hail created a dense mixture of hail and water, blocking drains and making travel difficult, as well as creating a dense fog, adding to the severity of the floods and hampering rescue efforts.
On Christmas Day, one of the largest Christmas tornado outbreaks occurred. A large line of thunderstorms suddenly erupted in eastern Texas early on December 25, with a few immediately becoming supercells. Tornadoes began to develop, causing damage to areas in Louisiana, Mississippi, all the way to the Outer Banks (threat began to decline as the squall line approached the area), with at least three being EF3s (one was a long-tracked tornado), and eight being EF2s. Other tornadoes were reported through December 25–26, causing up to more than US$1 million in damages.
Polar front theory was developed by Jacob Bjerknes, derived from a dense network of observation sites in Scandinavia during World War I. This theory proposed that the main inflow into a cyclone was concentrated along two lines of convergence, one ahead of the low and another trailing behind the low. The trailing convergence zone was referred to as the squall line or cold front. Areas of clouds and rainfall appeared to be focused along this convergence zone. The concept of frontal zones led to the concept of air masses.
The best-known is cumulonimbus with mammatus, but the mamma feature is also seen occasionally with cirrus, cirrocumulus, altocumulus, altostratus, and stratocumulus. A tuba feature is a cloud column that may hang from the bottom of a cumulus or cumulonimbus. A newly formed or poorly organized column might be comparatively benign, but can quickly intensify into a funnel cloud or tornado. An arcus feature is a roll cloud with ragged edges attached to the lower front part of cumulus congestus or cumulonimbus that forms along the leading edge of a squall line or thunderstorm outflow.
Shortly after, strong wind shear caused the storm to deteriorate, leaving the low-level circulation exposed on the western side. Beryl weakened to a tropical depression the next day due to the lack of convection, and it continued westward without redevelopment. On September 5, a reconnaissance flight into the depression found winds of 65 mph (100 km/h); this was deemed unrepresentative of the actual intensity as it was recorded in a squall line. The depression became disorganized once more and by September 6, it was no longer identifiable on satellites.
Like the system in Ontario but unlike the squall line of the upper Midwest, this was a continuous series of storms that produced widespread damage along its path. The most significant line began in western Maryland, then tracked north-northeastward into southeastern Pennsylvania, northern New Jersey and the northern suburbs of New York City before tracking eastward into southern New England. The system generally moved in an easterly direction, with new cells popping up further north as old cells dissipated. The first cells affected the southernmost part of Pennsylvania and western New Jersey.
Intense bow echoes responsible for widespread, extensive wind damage are called derechos, and move quickly over large territories. A wake low or a mesoscale low-pressure area forms behind the rain shield (a high pressure system under the rain canopy) of a mature squall line and is sometimes associated with a heat burst. Squall lines often cause severe straight-line wind damage, and most non-tornadic wind damage is caused from squall lines. Although the primary danger from squall lines is straight-line winds, some squall lines also contain weak tornadoes.
A warm front was likely to develop along the leading edge of the system, allowing for atmospheric instability, a necessary component of severe thunderstorms. In areas farther north, relatively cool temperatures were anticipated to limit convective activity but very strong dynamics in the area would allow storms to develop. This would allow a thunderstorm which became separated from the main squall line to become severe and possibly tornadic. Later in the day, the Storm Prediction Center (SPC) issued a slight risk for a large area which encompassed much of the Southeast United States.
During the early-morning hours of April 13, the pre-frontal squall line shifted eastward into eastern Georgia and the Carolinas, with numerous well-organized embedded supercells forming within the line, producing many strong tornadoes across the region. An EF3 tornado was confirmed south of Thomaston to northwest of Redbone in Georgia. A second EF3 tornado from south- southeast of Westminster to west of Central in South Carolina killed one person and caused major damage in Seneca. Yet another EF3 tracked from east- northeast of Elko to west-southwest of St. Matthews in South Carolina caused two more fatalities.
During the early morning hours April 13, the storms that formed the day before congealed into a strong squall line as they advanced into eastern Georgia and the Carolinas. Multiple embedded circulations and semi-discrete supercells within the line spawned numerous strong and deadly tornadoes across the region. A total of 10 tornadoes of EF3 or greater strength occurred on day two of the outbreak, including eight in South Carolina, where nine tornado-related fatalities occurred. A high-end EF3 tornado struck Seneca, South Carolina, destroying multiple homes and a manufacturing plant, killing one person and injuring five.
Later that day, a large portion of the southern Great Plains was in line for severe storms, along with parts of the Ohio Valley. During the afternoon, a squall line with several embedded supercells formed from Oklahoma to Indiana, producing tornadoes in Oklahoma, Illinois, and Arkansas. A large EF2 tornado touched down near Everton, Arkansas before moving through the southeastern part of town, causing significant damage to homes, a school, outbuildings, and trees. Three EF1 tornadoes also touched down in Arkansas, one of which tracked between Gassville and Mountain Home, inflicting considerable damage to some homes.
Conceptual airflow in a squall line with the Rear-inflow jet shown The rear- inflow jet is a component of bow echoes in a mesoscale convective system that aids in creating a stronger cold pool and downdraft. The jet forms as a response to a convective circulation having upshear tilt and horizontal pressure gradients. The cold pool that comes from the outflow of a storm forms an area of high pressure at the surface. In response to the surface high and warmer temperatures aloft due to convection, a mid-level mesolow forms behind the leading edge of the storm.
The Storm Prediction Center (SPC) had stated as early as February 8 that a few supercells would possibly develop on the 10th and could produce large hail, damaging winds, and a few tornadoes. When the thunderstorm outlook was issued for the 10th, the SPC stated that only a marginal chance for severe thunderstorms existed and that only a few storms would develop. Most of the severe weather activity was expected to develop along the cold front in the form of a squall line. A 10% chance of isolated tornadoes was introduced as the instability remained marginal for the event.
Activity was expected to be scattered at first, with some isolated supercells capable of producing tornadoes, but a squall line was anticipated to develop quickly and become the dominant feature. In the Northeast and Great Lakes region, southwesterly flow ahead of the trough brought warm, moist air into the area. Moderate instability, with CAPE values ranging from 1,000–2,000 J/kg and steep lapse rates were supporting of damaging straight-line winds, especially across Michigan, New York and Massachusetts. Later on, instability increased in the Northeast along a quasi-stationary front, leading to the risk of isolated supercells and a mesoscale convective system.
Damage to home in a subdivision in Madison County, Kentucky, from an EF-3 tornado on May 8, 2009. As the squall line continued east, it began to break apart into separate supercells; several of these supercells produced tornadoes. An EF-3 tornado touched down in eastern Garrard County before tracking into southern Madison County, Kentucky; two people were killed in this tornado, five others were injured, and 150 homes were damaged. All of the injuries and deaths occurred in one mobile home near the intersection of Kentucky Route 1295 and Kentucky Route 52 in southern Madison County.
Image showing the pressure pattern around an organized thunderstorm complex. Near the strong wake low, strong winds and a temperature spike were recorded A wake low, or wake depression, is a mesoscale low-pressure area which trails the mesoscale high following a squall line.. Due to the subsiding warm air associated with the system's formation, clearing skies are associated with the wake low. Once difficult to detect in surface weather observations due to their broad spacing, the formation of mesoscale weather station networks, or mesonets, has increased their detection.Mark R. Conder, Steven R. Cobb, and Gary D. Skwira (2006).
Conditions favorable for thunderstorm types and complexes There are four main types of thunderstorms: single-cell, multi-cell, squall line (also called multi-cell line) and supercell. Which type forms depends on the instability and relative wind conditions at different layers of the atmosphere ("wind shear"). Single-cell thunderstorms form in environments of low vertical wind shear and last only 20–30 minutes. Organized thunderstorms and thunderstorm clusters/lines can have longer life cycles as they form in environments of significant vertical wind shear, normally greater than in the lowest of the troposphere,Markowski, Paul and Yvette Richardson.
In addition to the tornadoes, there was widespread wind damage (over 1,400 severe weather reports were received by the Storm Prediction Center, with the vast majority being damaging winds) as an extremely large squall line/serial derecho tracked across the southern United States with wind gusts as high as 90 mph (145 km/h) reported across 20 states, killing at least 9 people, one of the deaths was as a result of an EF2 tornado in Dodge County, Georgia. Numerous power outages also took place due to the extensive wind damage. Nearly 100,000 and 147,000 residences lost power in Tennessee and Georgia respectively.
Along the leading edge of strong forcing, a severe squall line developed across central Florida northward into southern Virginia, leading to hundreds of damaging wind reports throughout the region. Ahead of this line, multiple long-lived supercells tracked across the Carolinas and into southern Virginia, with others developing as far north as Pennsylvania. Several strong tornadoes touched down within this corridor, where mid-level CAPE reached 1,000 J/kg and low-level wind shear profiles became conducive for tornadoes. Overall, 12 tornadoes touched down in North Carolina, the state's sixth largest outbreak on record in a single day.
Tornadoes alone were responsible for $1.067 billion in damage, with the EF4 tornado that struck Washington, Illinois accounting for $935 million of the total. In addition to structural damage, widespread power outages affected thousands of electricity customers across the same regions impacted by the tornado outbreak and subsequent squall line. Non-tornadic deaths and injured include one killed in Jackson County, Michigan, when a tree fell on a car, one killed by live wires in Shiawassee County, Michigan, one killed after touching a downed wire in Detroit, and two minor injuries in a home damaged by wind in Ohio.
Conditions favorable for thunderstorm types and complexes There are four main types of thunderstorms: single-cell, multi-cell, squall line (also called multi-cell line) and supercell. Which type forms depends on the instability and relative wind conditions at different layers of the atmosphere ("wind shear"). Single-cell thunderstorms form in environments of low vertical wind shear and last only 20–30 minutes. Organized thunderstorms and thunderstorm clusters/lines can have longer life cycles as they form in environments of sufficient moisture, significant vertical wind shear (normally greater than in the lowest of the troposphere)Markowski, Paul and Yvette Richardson.
A very powerful cold front tracked across the central US on January 29, with extremely cold weather behind the front. A moderate risk of severe weather was issued for parts of the lower Ohio Valley. Five tornadoes were reported across the region, although most of the damage was due to straight-line winds from a serial derecho which caused significant and widespread damage across the Ohio Valley region with winds of up to . It was later found that two people were killed in a mobile home in Posey County, Indiana by an isolated EF2 tornado embedded in the squall line.
The line strengthened as it moved through Alabama, partially due to a high amount of low-level moisture from the Gulf of Mexico and increasing wind shear. A majority of the tornadoes embedded in this initial squall line were weak, though several were strong and as such caused significant damage. An EF3 tornado caused major damage to homes in Coaling, Alabama, an EF2 and an EF3 tornado produced severe damage and a fatality near Eupora, Mississippi. Another EF3 tornado resulted in heavy damage in downtown Cordova, Alabama, which was struck by a violent EF4 tornado later that afternoon.
Multiple additional weak tornadoes occurred in Texas and in other states that afternoon and evening as well. Overnight into the early hours of April 30, the activity pushed eastward and a powerful squall line of severe thunderstorms with numerous embedded tornadic circulations swept through the Mississippi Valley. Throughout the day, the low tracked northeast into the Plains and intensified, causing some snowfall in the mountainous regions and in colder places, meanwhile severe weather continued to occur in the South. Forty-two tornadoes occurred across the Southern United States that afternoon and evening, with much of the activity centered in Mississippi.
In Nebraska, a long- track, multiple-vortex EF2 tornado passed near Bayard, tearing the roof and an exterior wall from a house, denuding trees, twisting irrigation pivots, damaging outbuildings, and destroying a garage. A separate brief EF1 tornado touched down in Bayard, causing considerable damage to a nursing home. In the late afternoon and early evening, the supercells merged into a squall line and produced isolated damaging wind gusts across South Dakota. The next day, the Storm Prediction Center issued an enhanced risk for severe weather, including a 10% risk area for tornadoes across parts of the Dakotas and Minnesota.
Furthermore, the subtropical jet stream was displaced unusually far south, reaching into the Pacific Ocean near Central America and extending toward Honduras and Jamaica. Intense ageostrophic flow was noted over the southern United States, with winds flowing perpendicular to isobars over Louisiana. As the area of low pressure moved through the central Gulf of Mexico, a short wave trough in the northern branch of the jet stream fused with the system in the southern stream, which further strengthened the surface low. A squall line developed along the system's cold front, which moved rapidly across the eastern Gulf of Mexico through Florida and Cuba.
A squall line which moved offshore New York and southern New England formed a mesoscale convective vortex, which fired new thunderstorm activity each day as it moved within the westerlies across the northern Atlantic. Once it reached mid-ocean, an increasingly northerly steering flow dropped the system down into the subtropics to the east of Bermuda, and it maintained decent organization. By 2100 UTC on July 24, the National Hurricane Center began classifying the system as Tropical Depression Two. In the first advisory on the depression, it was noted that the previous tropical depression was erroneously classified as Tropical Depression Two.
Over 300,000 people in Michigan were left without power due to the storm. Storm over Lancaster County, Pennsylvania on June 10 On June 10, a powerful squall line of thunderstorms with embedded supercells developed across New York and moved northeast through parts of northern New England and Quebec. Particularly hard hit was the Montreal region and its southern suburbs including Longueuil, Châteauguay, Brossard and Saint-Jean-sur-Richelieu. Barns were reported damaged and other structures sustained roof and siding damage; particularly in the Saint-Blaise-sur-Richelieu area where one home was pushed from its foundation.
The trailing convergence zone was referred to as the squall line or cold front. Areas of clouds and rainfall appeared to be focused along these convergence zones. A conveyor belt, also referred to as the warm conveyor belt, is a term describing the flow of a stream of warm moist air originating within the warm sector (or generally equatorward) of an extratropical cyclone in advance of the cold front which slopes up above and poleward (north in the Northern Hemisphere and south in the Southern Hemisphere) of the surface warm front. The concept of the conveyor belt originated in 1969.
An unusually intense squall line with embedded strong tornadoes struck Oregon and Washington on Wednesday, April 5, 1972. Of the four tornadoes, the most catastrophic event was a deadly F3 tornado that struck Portland, Oregon, and Vancouver, Washington, the first F3 tornado to strike Oregon since June 3, 1894. Dubbed the 1972 Portland-Vancouver Tornado, the tornado tracked across the heavily populated Portland–Vancouver metropolitan area, causing heavy damage, killing six people, and injuring 300 while causing $25.25 million (1972 USD) in damage. It was the deadliest tornado in the United States in 1972 and remains the deadliest tornado in the history of the Pacific Northwest.
Damage in Lone Grove, Oklahoma caused by an EF4 tornado on February 10. For February 10, the Storm Prediction Center issued a moderate risk for severe weather for portions of eastern Oklahoma, northeastern Texas, western Arkansas, and northwest Louisiana. It was projected that supercell thunderstorms would form late in the afternoon with a squall line developing during the evening. During the afternoon, an EF1 tornado touched down northwest of Warr Acres, near the Northwest Expressway, resulting in damage to several businesses in the area. Afterwards, an EF2 tornado struck Edmond, where six homes were destroyed, eight structures received major damage, 51 received minor damage and another 166 structures were affected.
Radar image of the bow echo crossing Kansas City just after 2:00 am CDT In the overnight hours of May 2, the supercells re-organized into a squall line/serial derecho that moved across the eastern Great Plains. Significant damage was reported across the Kansas City area, particularly in the Gladstone area near 77th Street and Euclid and northwest of Liberty near 108th Street and Cookingham were several homes and businesses were severely damaged or destroyed, including an Arby's restaurant. Several other commercial structures and homes sustained significant damage and railway cars were also overturned. Forty-thousand Kansas City Power & Light customers were left without power.
However, tornadic activity was limited to November 17, as individual supercell thunderstorms tracked across the Midwest United States, at times producing long-tracked tornadoes. The first tornadoes formed over Illinois, while the final tornadoes developed over Tennessee. Towards the end of November 17, these individual systems had merged into an extensive squall line that tracked eastward across the Mid-Atlantic states, producing damaging wind before exiting into the Atlantic Ocean early on November 18\. With damage estimated at approximately $1.6 billion, the tornado outbreak became the seventh weather event and fifth tornado outbreak in the U.S. to accrue over $1 billion in damage that year.
Several other tornadoes were reported across both Texas and Oklahoma ahead of a powerful squall line, and significant wind damage from a serial derecho was reported in the overnight hours. Eight tornadoes were confirmed on April 9 and the early morning hours of April 10, including two EF0, four EF1 and two EF2. Also on April 10, two tornadoes were reported in Southeastern Missouri, with both being confirmed as EF0 tornadoes. Several other tornadoes were reported during the evening across Southern Iowa, where there were reports of damage. Five tornadoes were reported across the Des Moines, Iowa coverage area, with two being rated EF0 while the other three were rated EF1.
Damage from this storm was visible along Business I-40 and US 421 in southwest Winston-Salem. The historic Old Salem area was also hard hit; many century-old trees in Salem Square and God's Acre were heavily damaged by the winds and had to be removed. Due to the difficulty in getting heavy equipment into the cemetery Gods Acre, those trees were removed by a helicopter. In the surrounding areas of Forsyth County, North Carolina, two other tornadoes were confirmed between 5:30 and 6:15 P.M. Strong winds associated with the same squall line downed a radio transmission tower in nearby High Point.
The captain instead elected to continue the flight into the edges of the squall line. Dr. Ted Fujita, a renowned weather researcher and professor of meteorology at the University of Chicago, was hired by British Aircraft Corporation, the manufacturer of the BAC 1-11, to study how the weather affected the jet. Dr. Fujita is recognized as the discoverer of downbursts and microbursts and also developed the Fujita scale, which differentiates tornado intensity and links tornado damage with wind speed. Notably, the accident was the first with a U.S.-registered aircraft in which a cockpit voice recorder (CVR) was used to aid in the investigation.
Organized areas of thunderstorm activity reinforce pre-existing frontal zones, and can outrun cold fronts. The resultant mesoscale convective system (MCS) often forms at the point of the strongest divergence of the upper-level flow in the area of greatest low-level inflow and convergence. The convection tends to move east or toward the equator, roughly parallel to low-level thickness lines and usually somewhat to the right of the mean tropospheric flow. When the convection is strongly linear or slightly curved, the MCS is called a squall line, with the strongest winds typically occurring just behind the leading edge of the significant wind shift and pressure rise.
Light tables were important to the construction of surface weather analyses into the 1990s The use of frontal zones on weather maps began in the 1910s in Norway. Polar front theory is attributed to Jacob Bjerknes, derived from a coastal network of observation sites in Norway during World War I. This theory proposed that the main inflow into a cyclone was concentrated along two lines of convergence, one ahead of the low and another trailing behind the low. The convergence line ahead of the low became known as either the steering line or the warm front. The trailing convergence zone was referred to as the squall line or cold front.
Strong thunderstorms were now scattered throughout the warm sector and a line of severe thunderstorms was occurring near the dry line. The Tri-State supercell appeared to still be discrete and isolated, with a severe storm north of Cairo, Illinois, placed well to its south. By 6 PM, the shortwave axis was over eastern Missouri and was lifting northeast. At 7 PM, the low was placed near Indianapolis, Indiana, with numerous thunderstorms east and south of the low and a squall line moving into the southeastern U.S. Cold air advection behind the strong cold front fed into the cyclone as snow and sleet fell from eastern Iowa to central Michigan.
The resultant mesoscale convective system (MCS) forms at the point of the upper level split in the wind pattern in the area of best low level inflow. The convection then moves east and toward the equator into the warm sector, parallel to low-level thickness lines. When the convection is strong and linear or curved, the MCS is called a squall line, with the feature placed at the leading edge of the significant wind shift and pressure rise which is normally just ahead of its radar signature. This feature is commonly depicted in the warm season across the United States on surface analyses, as they lie within sharp surface troughs.
However, breaks in the squall line allowed supercells to form in the overnight hours, and early on the 16th, the deadly tornado in southern North Carolina formed at the end of the outbreak. Three other deaths occurred that were not related to tornadoes; one was a utility worker that was electrocuted checking downed power lines in South Carolina and two were in car crashes in North Carolina related to severe thunderstorms. In total, 32 tornadoes were confirmed. Additionally, this was the last outbreak that used the original Fujita scale for measuring tornado intensity, as it was being superseded by the Enhanced (EF) scale in January 2007.
In mid-March 1933, most of the Tennessee and Mississippi Valleys experienced a very warm late winter season due to a warm southerly flow coming in from the Gulf of Mexico, which bumped temperatures into the upper 70s and low 80s °F on March 14—well above normal temperatures in the upper 40s and low 50s °F. Two extratropical low pressure systems were moving across the central part of the continent with one storm centered over the Great Lakes and another one over Arkansas. With the southern storm, a cold front swiftly neared from the west and produced a squall line of thunderstorms along it.
The storm also began to transition into an extratropical cyclone, achieving a peak of two times on March 23. Blizzard warnings were issued for areas around Denver due to the strong winds accompanying the system along with snowfall. Parts of Interstate 80 were shut down due to the extreme winter weather conditions Ahead of its cold front, thunderstorms began to fire up, prompting the National Weather Service to issue a tornado watch. A squall line later developed out of this as more storms began to fire up and move eastwards, with the severe weather threat shifting more to the east towards the East Coast.
A special marine warning (SAME code SMW) is a warning issued by the U.S. National Weather Service for potentially hazardous marine weather conditions usually of short duration (up to 2 hours) producing sustained marine thunderstorm winds or associated gusts of 34 knots or greater; or hail 3/4 inch or more in diameter; or waterspouts affecting areas included in a coastal waters forecast, a nearshore marine forecast, or a Great Lakes open lakes forecast that is not adequately covered by existing marine warnings. It is also used for short duration mesoscale events such as a strong cold front, gravity wave, squall line, etc., lasting less than 2 hours and producing winds or gusts of 34 knots or greater.
With the presence of an extremely unstable air mass over central Oklahoma, the Storm Prediction Center issued a Particularly Dangerous Situation Tornado Watch for much of the state during the afternoon of May 31 and lasting into the night. Later that evening, severe storms rapidly developed, and an extremely large and violent multiple-vortex tornado devastated areas near El Reno, Oklahoma, and killed eight people including three men from the storm chasing crew, TWISTEX. The tornado had been rated EF5 based on mobile radar readings, Other weak tornadoes and major flooding devastated parts of the Oklahoma City metro that evening. Further north, a powerful squall line of severe storms with several embedded strong tornadoes developed in Missouri.
In December 1917, Assistant Secretary of the Navy, Franklin Delano Roosevelt asked Dr. Alexander McAdie, director of Harvard's Blue Hill Meteorological Observatory, to train weather officers for the U.S. Navy. The Navy sent Reich to take the course, thus kindling his interest and launching his career in the field. He received training as a U.S. Navy pilot and received his wings, meanwhile providing meteorological support for the first transatlantic flight of the Navy's NC-4. In 1919, while assigned to the Naval Air Station at Hampton Roads, Virginia, he encountered Billy Mitchell (US Army general regarded as father of the US Air Force) who was forced to land a light plane on the beach ahead of a squall line.
Another strong tornado caused damage to homes in the town of Pawnee Rock, Kansas before it passed near Great Bend, debarking trees and completely destroying farm homes at high- end EF3 strength. Another EF3 tornado moved through four counties in Wisconsin, destroying a mobile home park near Chetek, snapping and uprooting countless trees, and destroying a frame home near Conrath. The Chetek/Conrath tornado was officially the longest-tracked tornado in Wisconsin state history, and killed one person while injuring 25 others. Tornado activity was not as intense on May 17, though an EF2 embedded in a squall line ripped the roof off of a house near Galva, Illinois, injuring one person.
Later that night and into the early morning hours of April 14, the storms merged into a large squall line and pushed eastward across parts of the Southern United States. An enhanced risk of severe weather was issued for parts of Louisiana, Mississippi, and Alabama, including a 10% risk of tornadoes. A large EF1 tornado moved through Shreveport, Bossier City, and Red Chute, Louisiana during the early morning hours and downed many trees, one of which fell onto a travel trailer and killed a child inside. An EF2 tornado near Bryceland destroyed barns and ripped much of the roof off of a home as well, while another EF2 near Carencro damaged homes and businesses along its path.
This TRMM weather satellite shows the wind impact of a Tehuantepecer from December 16, 2000 at 1315 UTC. Its leading edge shows up as a rope cloud within the visible and infrared channels of weather satellite images, and since it lies at the leading edge of a density (temperature and dew point) discontinuity, its leading edge by definition it is a cold front, though it has also been described as a squall line, with embedded rain squalls sometimes seen. Within polar orbiting imagery, a corridor of strong low-level winds show up this feature within scatterometer data retrievals, with its leading edge at the south to southwest edge of the wind surge.
In both places, rain was falling at rates of per hour. The large volume of moisture dragged behind Post-Tropical Cyclone Cristobal as it moved to the north prompted a rare moderate risk of severe thunderstorms to be issued for large portions of Michigan, Indiana and Ohio by the Storm Prediction Center in their categorical outlook. A squall line associated with Cristobal's remnants, later classified as a derecho, brought wind gusts up to around the areas; 650,000 people lost power due to the derecho from Indiana and Michigan to western New York. The derecho produced a damaging EF2 tornado in Beaver County, Pennsylvania and two EF0 tornadoes in Columbiana County, Ohio on June 10.
The tornado outbreak of January 10–11, 2020 was a two-day severe weather event stretching from the South-Central Plains eastward into the Southeast United States. An eastward-moving shortwave trough tracked across the continental United States through that two-day period, combining with abundant moisture, instability, and wind shear to promote the formation of a long-lived squall line. Hundreds of damaging wind reports were received, and 80 tornadoes occurred within this line, making it the third largest January tornado outbreak on record. Three tornadoes—an EF1 in eastern Texas, an EF2 in northern Louisiana, and an EF2 in western Alabama—led to a total of seven deaths, all in mobile homes.
Reckless pilots have exploited squalls by flying in front of thunderstorm systems as if flying along a ridge. The pilot really must land at an airport and put the glider in a hangar; the squall line will catch him again soon and imperil the glider if it is not protected. Dennis Pagen performed a similar flight in front of a supercell cumulonimbus during the Preliminaries of the hang glider 1990 World championship in Brazil where he was able to fly 35 km at high speed without a turn. The author acknowledges that his achievement was dubious, since hang gliders (and even more so paragliders) are significantly slower than sailplanes and can much more easily be sucked inside the cloud.
While a significant severe weather event was expected, the extreme nature caught many forecasters by surprise, based on the risk levels and the probabilities estimated by the SPC in the area primarily affected. Farther north, the initial thunderstorm development in eastern Missouri quickly developed into a squall line, eventually becoming a derecho that produced many embedded – and generally weak – tornadoes and widespread wind damage across Illinois, Indiana, Kentucky, and Ohio. Springfield, Illinois, which was struck by two tornadoes less than a month earlier, was hit again by tornadoes and damaging straight-line winds of up to , as was the St. Louis, Missouri area. The storm quickly tracked through Indiana, Ohio, and Kentucky with a peak wind gust of in Lexington, Kentucky.
Underneath the potent mid-level flow, rich low-level moisture was forecast to surge into western Kansas and eastern Colorado while mid-level CAPE values were projected to top 3,000 J/kg. While initiation of thunderstorms was expected in the early afternoon hours (with the threat for large hail being the primary threat initially in the presence of weak low- level wind shear), more expansive cloud cover and a stronger cap delayed initiation. Later in the day, a cluster of storms formed across portions of Nebraska and Kansas, with a severe squall line taking shape farther south across the Texas and Oklahoma panhandles as stronger upper-level winds arrived. Numerous tornadoes were reported throughout the area, most of which were weak.
Steep lapse rates were forecast to contribute to mid-level Convective Available Potential Energy (CAPE) values of 2,500–3,000 J/kg across eastern Texas, with slightly lower values of 1,000–2,000 J/kg over portions of Louisiana and Mississippi. Intense speed and directional shear throughout the entirety of the atmosphere led to large, looping hodographs, and effective storm relative helicity values ranging from 250–600 J/kg along and south of the aforementioned warm front as depicted by forecast atmospheric soundings. The culmination of these ingredients was forecast to support an outbreak of supercell thunderstorms across the Moderate risk, with the potential for strong to violent (EF2+) tornadoes with the most sustained cells, followed by the development of an eastward-progressing squall line overnight.
A Slight risk was issued for most of Southern and Northeastern Ontario. The slight risk zone extends from southern Quebec, near Montreal into northern Mexico During the noon hours, the moderate risk zone was extended further south to includes portions of western New York, western Pennsylvania, northern West Virginia, northern Kentucky, southeastern Indiana, most of Ohio and larger portions of southern Ontario from Windsor to eastern Ontario. It turned out to be a long squall line though, and while there was wind damage from winds as strong as stretching from the Tennessee Valley north to almost Hudson Bay, there were only two tornadoes, one near Brantford southwest of Toronto and the other near Bancroft north of Peterborough, Ontario.National Post weather information, courtesy of Canada.
Satellite image of the Storm in the Midwest on December 25th Moving ashore on the West Coast of the United States on December 23, an extratropical storm system moved through the Southwest, dumping heavy snowfall before emerging into the High Plains on December 24–25. Prior to its passage through much of the United States, it was expected to drop of snow, creating havoc for Christmas travelers. The system brought the potential for severe thunderstorms as well, with two tornadoes and severe winds produced across the central U.S. After the cyclone moved ashore, it dove southeast, weakening somewhat as it began to slowly eject into the High Plains. A squall line begin to coalesce along the system's cold front as the low began to deepen somewhat.
On 22 December, the storm brought freezing rain to the state of Maine. The storm caused freezing rain to accumulate on tree branches, causing some to fall off and topple power lines. The storm complex continued to crank out ice and snow in the northern parts of New England and Canada, before finally weakening and dissipating late on 23 December. The storm complex was also responsible for producing a small but damaging tornado outbreak that occurred from 20–21 December, most of which occurred on 21 December, due to the fact that supercell thunderstorms were able to pop up, and eventually coalesced into a squall line later the same day along the system's cold front, as it tracked towards the East Coast.
Shelf clouds most often appear on the leading edge of a thunderstorm as they are formed by condensation from cool outflow of the storm that lifts warmer air in the ambient environment (at the outflow boundary). When present in a supercell thunderstorm these shelf clouds on the leading edge of a storm are associated with the forward flank downdraft (FFD). Shelf clouds in supercells also form with the rear flank downdraft (RFD), although these tend to be more transitory and smaller than shelf clouds on the forward side of a storm. A wall cloud will usually be at the rear of the storm, though small, rotating wall clouds (a feature of a mesovortex) can occur within the leading edge (typically of a quasi-linear convective system (QLCS) or squall line) on rare occasion.
Picture of an EF-0 tornado north of Royalton, Illinois, on May 8, 2009 As the initial line weakened, the mesoscale convective vortex on the northern end began to strengthen and separate from the squall line. A long-lived supercell formed within the MCV in Madison County, Missouri, producing hail up to baseball size and a few tornadoes, in addition to the more widespread, damaging, straight-line winds throughout the area. Numerous trees were knocked over from Shannon County, Missouri—near the Current and Jacks Fork rivers, in the Ozark National Scenic Riverways preserve—northward through the Mark Twain National Forest and other forested public conservation lands. Devastation was especially pronounced in the area west of Ironton, Missouri, around the popular Johnson's Shut-Ins State Park and the Bell Mountain Wilderness area.
Both tornadoes were rated as EF2. The same storm system and its associated cold front produced a bow echo that traveled through Michigan, most of Southern Ontario and parts of Southern Quebec where a second squall line formed in eastern Ontario. With the squall lines, one F0 tornado was confirmed by Environment Canada investigators in Ottawa, Ontario tracking about through the Britannia, Lincoln Heights and Carlington Heights communities where it tore off the roofs of two apartment complexes, downed numerous trees, power lines and signs. Widespread heavy damage was reported elsewhere including to planes at the Rockcliffe Airport as well as trees, power lines, street signs and several other buildings including houses and a school elsewhere across the city and in Gatineau, Quebec due to winds locally at .
In accordance, the storm was given the name Utor; this name had been submitted by the United States and means "squall line". Utor's development following its naming was slow, but quickened as the tropical storm neared the Philippines. The tropical cyclone reached the southeastern coast of Samar by 06:00 UTC on December 9 and began tracking through the central Philippine archipelago over the next two days. Despite its interaction with the nearby islands, Utor continued to strengthen without much impediment and reached typhoon strength in the Visayan Sea at 12:00 UTC that day. Twelve hours later, the typhoon attained an initial peak intensity with maximum sustained winds of 140 km/h (85 mph) and a minimum barometric pressure of 955 mbar (hPa; 28.20 inHg) in the Sibuyan Sea according to the JMA.
The first indications for an organized severe weather event came on April 9, when the Storm Prediction Center (SPC) outlined a risk area across much of the Ark-La-Tex region. The following day, a broader region for severe thunderstorms was introduced, with a heightened threat level across far eastern Texas into western Mississippi. A day 3 enhanced risk was outlined across those same regions on April 11, although SPC noted concerns about system timing and the availability of instability as numerous storms developed. As weather models came into broad consensus with regard to the potential for discrete supercell thunderstorms and a succeeding squall line, confidence in a significant severe weather outbreak increased, prompting the SPC to issue a day 2 moderate risk across far eastern Texas, northern Louisiana, southeastern Arkansas, and far western Mississippi.
The turning point of the game was a 21-yard touchdown pass from Vad Lee to Darren Waller with 30 seconds remaining in the half to dent the deficit back to six and allowing Georgia Tech to head to the locker room with the momentum. A squall line came over Bobby Dodd Stadium at the start of the third quarter causing sloppy play from UNC which along with Tech's improved defense prevented the Tar Heels from scoring in the second half. Paul Johnson from there on out decided to dominate the time of possession wearing down UNC's defense allowing for the Yellow Jackets to add two more rushing touchdowns for a come from behind 28–20 victory, bringing Georgia Tech to 3–0 for the season and 2–0 in conference play.
Ludwig Dettmann and Theo Matejko made an artistic record of the flight. On the third day of the flight, a large section of the fabric covering of the port tail fin was damaged while passing through a mid- ocean squall line, and volunteer riggers (including Eckener's son, Knut) repaired the torn fabric. Eckener directed Rosendahl to make a distress call; when this was received, and nothing else was heard from the airship, many believed it was lost; but because the zeppelin had to fly at reduced speed to repair the damaged fin, the airship's wind-driven generator could not produce enough power to send messages. After the ship arrived safely there was some annoyance from the Lakehurst personnel that it had not answered repeated calls for its position and estimated arrival time.
Severe weather, in form of strong straight-line winds can be expected in areas where the squall line itself is in the shape of a bow echo, within the portion of the line which bows out the most. Tornadoes can be found along waves within a line echo wave pattern, or LEWP, where mesoscale low pressure areas are present. Some bow echoes that develop within the summer season are known as derechos, and they move quite fast through large sections of territory. On the back edge of the rain shield associated with mature squall lines, a wake low can form, which is a mesoscale low pressure area that forms behind the mesoscale high pressure system normally present under the rain canopy, which are sometimes associated with a heat burst.
MV Dongfang zhi Xing (; translated as Oriental Star or Eastern Star) was a river cruise ship that operated in the Three Gorges region of inland China. On the night of 1 June 2015, the ship was traveling on the Yangtze River when it capsized during a thunderstorm in Jianli, Hubei Province with 454 people on board. On 13 June, 442 deaths were confirmed, with 12 survivors (including 2 rescued by officials). The passengers were mostly in their 60s and 70s, and mostly from Nanjing, where the ship started its cruise. The final investigation concluded the ship navigated into a squall line (the biggest scale of thunderstorm) from 21:19 onwards, blasted by a downburst (a form of windshear) from 21:26 to 21:32, capsized at 21:31, and sank at 21:32.
While the northern part of the system was producing severe damage in Canada (northeastern Ontario and southern Quebec), an associated cold front led to significant damage in the US Midwest and Southern Ontario as it crossed the area later that same evening. There were dozens of reports of significant wind or tornado damage, especially in Michigan but also in southern Ontario, Wisconsin, Illinois, Iowa, and as far south as northern Missouri. The setup was similar along the long cold front, and the hot, humid air mass led to the damaging derecho, although the stronger derecho that affected areas well north of there formed much earlier that day in Upper Michigan just before noon local time. It had a clearly defined bow echo (squall line) formation, unlike these cells which were more fragmented.
N1335U, the aircraft involved in the accident, at Miami International Airport The flight crew consisted of Captain William W. "Bill" McKenzie, aged 54, a highly experienced pilot with 19,380 flight hours (including 3,205 hours on the DC-9), and first officer Lyman W. Keele Jr, aged 34, who had 3,878 flight hours, with 235 of them on the DC-9. The crew was advised of the presence of embedded thunderstorms and possible tornadoes along their general route prior to their departure from Huntsville, but they were not subsequently told that the cells had since formed a squall line. The flight crew had flown through that same area from Atlanta earlier in the day, encountering only mild turbulence and light rain. The weather system had greatly intensified in the meantime.
High-end EF2 damage to a house in Fort Payne, AL. A large shortwave trough progressed across the northern Plains on February 20, with an associated surface low-pressure area contributing to a blizzard across Michigan and Wisconsin. Within the warm sector of the cyclone, modest instability and moisture, as well as sufficient forcing along a cold front, initiated the development of a squall line across the Ohio River Valley and Mississippi River Valley by the afternoon. Strong wind shear led to widespread damaging wind reports in addition to over two dozen tornadoes across the Midwestern and Southern United States, four of which were rated EF2 on the Enhanced Fujita scale. The first two EF2s affected rural areas in Illinois near the towns of Martinsburg and Pana, damaging several farms.
Other tornadoes caused damage and injuries in the southern states including Louisiana and Mississippi. In addition to the tornadoes, there was widespread wind damage (over 1,400 severe weather reports were received by the Storm Prediction Center, with the vast majority being damaging winds) as an extremely large squall line/serial derecho, which had begun to form over northern Texas at around 4 am Monday morning, tracked across the southern United States with wind gusts as high as 90 mph (145 km/h) reported across 20 states. Severe wind damage and power outages also occurred in Arkansas, in addition to a few tornadoes. Nine people were killed in this storm, one of the deaths was as a result of an EF2 tornado in Dodge County, Georgia that destroyed mobile homes.
A moderate risk of severe weather was issued by the Storm Prediction Center for a large section of the Southeast for the night of the November 14 into November 15. The activity started in the overnight hours in Louisiana and Arkansas and tracked eastward, producing scattered tornadoes across the entire Gulf Coast and into the Carolinas over the next 36 hours. The most severe tornadoes took place in St. Helena Parish, Louisiana where one person was killed in a trailer, near Sumrall, Mississippi where an F3 tornado led to severe damage and numerous injuries, and in Montgomery, Alabama where an indoor roller skating park was destroyed with 30 children inside (but no serious injuries occurred there). When the line crossed into Georgia and northern Florida, it formed into a squall line.
This line is likely the point of further convection and storms, especially if it coincides with fronts from other thunderstorms in the vicinity. One can notice it at the leading edge of a squall line, in the southeastern quadrant of a typical supercell (in the northern hemisphere), or different regions around other thunderstorms. They may also be visible as an outflow boundary hours or days after convection and can pinpoint areas of favored thunderstorm development, the possible direction of movement, and even likelihood for tornadoes. The speed of forward movement of the outflow boundary or gust front to some degree modulates the likelihood of tornadoes and helps determine whether a storm will be enhanced by its presence or the inflow be choked off thus weakening and possibly killing the storm.
On the morning of 7 December, the UK was under the influence of a strong Atlantic low pressure system, which was named Ulrike, bringing unstable weather conditions to much of the UK, and the south in particular. At approximately 07:30 GMT, a small band of thunderstorms initialised over Cornwall moving east-northeast across the country. By approximately 10:00 am, the squall line had reached Salisbury, where a drop in humidity was recorded, which may have resulted in an increase of atmospheric pressure behind the squall, causing it to accelerate forward. This increased motion in combination with a change in wind direction ahead of the storm may have initialised the rotation of the mesocyclone in one of the now strong storm cells, resulting in the touchdown of the T4 tornado in Kensal Rise, London, at 11 am.
By April 29, a ridge of high pressure centered over the Atlantic Ocean, this helped focus high levels of atmospheric moisture rising from the Gulf of Mexico along the front, causing immense clusters of heavy rain and thunderstorms to slowly progress eastwards – also known as thunderstorm training. Simultaneously, after deepening slightly to , the elongated area of low pressure was producing heavy snowfall in parts of Nebraska and Colorado, including Denver. Little change occurred over the next six hours as the front moved slightly eastwards; although a squall line was beginning to form, increasing the threat for large hail, damaging wind gusts and a few tornadoes. While the overall setup was not favorable for a widespread tornado outbreak, thunderstorms from earlier in the day left behind an outflow boundary draped across northeastern Texas, resulting in a localized area of enhanced low-level helicity.
On May 30, two days before the outbreak, the Storm Prediction Center (SPC) noted the possibility of a severe weather event in the Northeastern United States in their outlook. A storm system was forecast to draw warm, moist air (with dew points over ) from the south, ahead of a driving cold front. In light of this, the SPC issued a slight risk for severe thunderstorms the area. As an upper-level trough moved over the Great Lakes, further moisture and warmth increased atmospheric instability in the area, raising the threat of a squall line or supercell thunderstorms. By June 1, the storm system moved over Ontario and Quebec, with a cold front trailing behind it over northern New England. CAPE values exceeded 4,000 J/kg, indicating an extreme amount of instability in the atmosphere, conducive to strong thunderstorms.
By the late evening, most of the discrete storms that existed earlier in the day had merged into squall lines and bow echoes, with any remaining mesocyclones embedded within these bands rather than individual storms. Forced along the extent of a cold front, the primary squall line raced eastward across Ohio at approximately 60 mph (95 km/h), reaching Pennsylvania by 0200 UTC. As a result of decreased atmospheric instability, the threat for tornadoes and hail had greatly diminished by this time, while the probability for damaging winds remained elevated to high; as a result, watches issued east of Ohio were severe thunderstorm watches rather than tornado watches. The final tornado associated with the outbreak was an EF0 that dissipated at 0340 UTC in Lincoln County, Tennessee (south of the area impacted by the main outbreak of tornadoes); based on Central Standard Time, this would have still occurred on November 17.
A warm front associated with the complex moved across the state during the daytime on May 20, followed by a cold front that swept eastwards across the state between the evening of May 20 into the following morning. This produced several episodes of severe thunderstorms enhanced by the confluence of the moist, warm, and unstable airmass ahead of the storm system. Initially isolated thunderstorms over eastern Oklahoma coalesced into a line, with new storm cells training repeatedly tracking over the same locations as the line slowly moved east. The complex combined with another cluster of storms over central Oklahoma and tracked northeast, causing further rainfall before dissipating. Another squall line was generated by the storm system as the associated upper-level low moved into Kansas, sweeping through eastern Oklahoma and northwestern Arkansas on the morning of May 21 with its heaviest rains overlapping the same areas affected by the earlier storms.
A shelf cloud along the leading edge of a derecho in Minnesota A derecho (, from , "straight" as in direction) is a widespread, long-lived, straight-line wind storm that is associated with a fast-moving group of severe thunderstorms known as a mesoscale convective system and potentially rivaling hurricanic and tornadic forces. Derechos can cause hurricane-force winds, tornadoes, heavy rains, and flash floods. In many cases, convection-induced winds take on a bow echo (backward "C") form of squall line, often forming beneath an area of diverging upper tropospheric winds, and in a region of both rich low-level moisture and warm-air advection. Derechos move rapidly in the direction of movement of their associated storms, similar to an outflow boundary (gust front), except that the wind remains sustained for a greater period of time (often increasing in strength after onset), and may exceed hurricane-force.
This feature led to the formation of a surface low over northern Mississippi and Alabama, aiding in the northern transport of rich and deep moisture originating from the Gulf of Mexico. Strong southwesterly low-level winds coupled with strong forcing for ascent along a trailing cold front led to the formation of a squall line stretching from the Carolinas down into portions of the Deep South. Ahead of this line, the combination of mid-level Convective Available Potential Energy of 500–1,200 J/kg, a low-level jet of 50–70 kn, and effective storm-relative helicity of 250–400 J/kg resulted in a highly unstable atmosphere that was conducive to the formation of strong tornadoes. The lack of strong convective inhibition, coupled with weak forcing, favored the formation of numerous discrete supercell thunderstorms across the Florida Panhandle, southeastern Alabama, much of central Georgia, and into South Carolina.
At approximately 01:30hrs (1:30am), both sides finally made visual contact with each other as the first Japanese ships emerged from the squall line only away from the entire US formation. Despite the Americans having steamed directly into the middle of the Japanese force, neither side opened fire for almost ten minutes as they passed by each other, with the Japanese ships enveloping the American battle column as they emerged from the darkness in three separate groups. In the second position of the rear, US Destroyer van USS Barton began to train her deck guns and torpedo tubes on several Japanese ships in her immediate area and awaited the order to open fire from the flagship. At 01:48hrs (1:48am) the order to open fire was precluded when lit its searchlights onto the cruiser , causing both sides to immediately open fire on each other and starting the First Naval Battle of Guadalcanal.
On May 20, a prominent central upper trough moved eastward with a lead upper low pivoting over the Dakotas and Upper Midwest. A Southern stream shortwave trough/moderately strong polar jet moved east-northeastward over the southern Rockies to the southern Great Plains and Ozarks area, with severe thunderstorms likely with peak heating. The Storm Prediction Center issued a moderate risk of severe thunderstorms during the early morning hours of May 20 from southeastern Missouri to north-central Texas, for the possibility of isolated strong tornadoes across central and eastern Oklahoma, in addition to the threat of large hail and damaging straight-line wind gusts. The most devastating event of the day occurred when a violent EF5 tornado struck Moore, Oklahoma, damaging or destroying more than 13,000 homes and killing 24 people including seven children who died while taking shelter inside Plaza Towers Elementary School, which was flattened by the tornado.The Tornado Outbreak of May 20, 2013 In Michigan, gusts from the squall line reached , downing numerous trees and power lines.
A shelf cloud such as this one can be a sign that a squall is imminent Organized areas of thunderstorm activity not only reinforce pre-existing frontal zones, but can outrun cold fronts in a pattern where the upper level jet splits apart into two streams, with the resultant Mesoscale Convective System (MCS) forming at the point of the upper level split in the wind pattern running southeast into the warm sector parallel to low-level thickness lines. When the convection is strong and linear or curved, the MCS is called a squall line, with the feature placed at the leading edge of the significant wind shift and pressure rise. Even weaker and less organized areas of thunderstorms lead to locally cooler air and higher pressures, and outflow boundaries exist ahead of this type of activity, which can act as foci for additional thunderstorm activity later in the day. These features are often depicted in the warm season across the United States on surface analyses and lie within surface troughs.
A high risk of severe weather was issued on April 16 for most of eastern North Carolina, and parts of southeast Virginia and northeast South Carolina The next day, a moderate risk of severe weather was issued for April 16 for the Carolinas and southern Virginia as the cold front tracked eastward and a mesolow developed across the Appalachians. As storms began moving into areas of strong atmospheric instability, a PDS Tornado Watch was issued shortly after noon and a high risk, the first of 2011, was issued shortly thereafter at 12:30 pm EDT (1630 UTC) for central and eastern North Carolina and immediate adjacent areas in South Carolina and Virginia. A squall line descended the Blue Ridge, and rapidly intensified along the Interstate 77 corridor. As this line tracked eastward, wind damage was reported in Salisbury and Lexington, where tree and roof damage was widespread. The Salisbury storm - an EF1 - became the first confirmed tornado from the outbreak in North Carolina, followed shortly thereafter by tornadoes near Monroe (EF0) and north of Burlington (EF1).
Since autumn and spring are transitional periods (warm to cool and vice versa) there are more chances of cooler air meeting with warmer air, resulting in thunderstorms. Tornadoes in the late summer and fall can also be caused by hurricane landfall. Not every thunderstorm, supercell, squall line, or tropical cyclone will produce a tornado. Precisely the right atmospheric conditions are required for the formation of even a weak tornado. On the other hand, 700 or more tornadoes a year are reported in the contiguous United States. On average, the United States experiences 100,000 thunderstorms each year, resulting in more than 1,200 tornadoes and approximately 50 deaths per year. The deadliest U.S. tornado recorded is the 18 March 1925, Tri-State Tornado that swept across southeastern Missouri, southern Illinois and southern Indiana, killing 695 people. The biggest tornado outbreak on record—with 353 tornadoes over the course of just 3 1/2 days, including four EF5 and eleven EF4 tornadoes—occurred starting on 25 April 2011 and intensifying on 26 April and especially the record-breaking day of 27 April before ending on 28 April.

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