A squall line, or more accurately a quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. Linear thunderstorm structures often contain heavy precipitation, hail, frequent lightning, strong straight-line winds, and occasionally tornadoes or waterspouts. Particularly strong straight-line winds can occur where the linear structure forms into the shape of a bow echo. Tornadoes can occur along waves within a line echo wave pattern (LEWP), where mesoscale low-pressure areas are present. Some bow echoes can grow to become derechos as they move swiftly across a large area. On the back edge of the rainband associated with mature squall lines, a wake low can be present, on very rare occasions associated with a heat burst.
A derecho 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.
The heat wave of 1995 derecho series are a series of derechos that occurred from July 11 through July 15, 1995 in the U.S. and Ontario, Canada. This weather event is one of the least known about but still notable weather events that occurred during the 20th century.
The Independence Day Derecho of 1977 was a derecho, or long-lived windstorm associated with a fast-moving band of thunderstorms, that occurred in the northern Great Plains of the U.S. on July 4, 1977. It lasted around 15½ hours. The derecho formed in Minnesota around 10 a.m. CDT on July 4 and became more intense around noon in the central part of the state. The derecho produced winds of 80-100 mph (130–160 km/h) in northern Wisconsin, felling thousands of trees.
The Boundary Waters–Canadian Derecho was an international derecho that occurred during the afternoon and evening hours of July 4 and the early morning hours of July 5, 1999. It traveled 1,300 miles (2,092 km) and lasted 22 hours.
The Southern Great Lakes Derecho of 1991 is the derecho event that occurred on July 7 and 8, 1991. It lasted 17 hours and raced from South Dakota through southern Michigan before dying out over Western Pennsylvania.
The New York State Labor Day Derechos were two derecho events that occurred on Labor Day, September 7, 1998. One derecho moved through northern and central New York state, and the other would start in southeastern Michigan and move through northeastern Ohio, Pennsylvania, New Jersey, and Long Island. A spokesman for the New York State Emergency Management Office, estimated that 300,000 residences had lost electricity, 7 persons died and 80 were injured.
The Columbus Day Storm of 1962 was a Pacific Northwest windstorm that struck the West Coast of Canada and the Pacific Northwest coast of the United States on October 12, 1962. Typhoon Freda was the twenty-eighth tropical depression, the twenty-third tropical storm, and the eighteenth typhoon of the 1962 Pacific typhoon season. Freda originated from a tropical disturbance over the Northwest Pacific on September 28. On October 3, the system strengthened into a tropical storm and was given the name Freda, before becoming a typhoon later that day, while moving northeastward. The storm quickly intensified, reaching its peak as a Category 3-equivalent typhoon on October 5, with maximum 1-minute sustained winds of 115 mph (185 km/h) and a minimum central pressure of 948 millibars (28.0 inHg). Freda maintained its intensity for another day, before beginning to gradually weaken, later on October 6. On October 9, Freda weakened into a tropical storm, before transitioning into an extratropical cyclone on the next day. On October 11, Freda turned eastward and accelerated across the North Pacific, before striking the Pacific Northwest on the next day. On October 13, the cyclone made landfall on Washington and Vancouver Island, and then curved northwestward. Afterward, the system moved into Canada and weakened, before being absorbed by another developing storm to the south on October 17. The Columbus Day Storm of 1962 is considered to be the benchmark of extratropical wind storms. The storm ranks among the most intense to strike the region since at least 1948, likely since the January 9, 1880 "Great Gale" and snowstorm. The storm is a contender for the title of the most powerful extratropical cyclone recorded in the U.S. in the 20th century; with respect to wind velocity, it is unmatched by the March 1993 "Storm of the Century" and the "1991 Halloween Nor'easter". The system brought strong winds to the Pacific Northwest and southwest Canada, and was linked to 46 fatalities in the northwest and Northern California resulting from heavy rains and mudslides.
The Late-May 1998 tornado outbreak and derecho was a historic tornado outbreak and derecho that began on the afternoon of May 30 and extended throughout May 31, 1998, across a large portion of the northern half of the United States and southern Ontario from southeastern Montana east and southeastward to the Atlantic Ocean. The initial tornado outbreak, including the devastating Spencer tornado, hit southeast South Dakota on the evening of May 30. The Spencer tornado was the most destructive and the second-deadliest tornado in South Dakota history. A total of 13 people were killed; 7 by tornadoes and 6 by the derecho. Over two million people lost electrical power, some for up to 10 days.
The Great Lakes Storm of 1913 was a blizzard with hurricane-force winds that devastated the Great Lakes Basin in the Midwestern United States and Southwestern Ontario, Canada, from November 7 to 10, 1913. The storm was most powerful on November 9, battering and overturning ships on four of the five Great Lakes, particularly Lake Huron.
The Western Wisconsin Derecho was a derecho, or severe weather system, that occurred through several counties of Western Wisconsin on July 15, 1980. It caused $240 million in damage (1980 dollars) -- the largest storm damage total in Wisconsin history to that point. Three people died. The storm is still referred to as The July 15th Storm,July 15th, 1980, or simply The Storm.
A bow echo is the characteristic radar return from a mesoscale convective system that is shaped like an archer's bow. These systems can produce severe straight-line winds and occasionally tornadoes, causing major damage. They can also become derechos or form Line echo wave pattern (LEWP).
The heat wave of 2006 derecho series were a set of derechos — severe winds with powerful thunderstorms — that occurred on July 17–21, 2006. The first storms hit a wide swath of north-central and northeastern North America that stretched from the Upper Midwest through much of Ontario and into the northeastern United States. Another round struck the middle Mississippi River Valley, including two derechos that hit St. Louis, Missouri. The storms left more than three million people without power, some more than once and some for weeks.
The Great Appalachian Storm of November 1950 was a large extratropical cyclone which moved through the Eastern United States, causing blizzard conditions along the western slopes of the Appalachian Mountains and significant winds and heavy rainfall east of the mountains. Hurricane-force winds, peaking at 110 miles per hour (180 km/h) in Concord, New Hampshire, and 160 mph (260 km/h) in the highlands of New England, disrupted power to 1 million customers during the event.
The Corn Belt derecho was a progressive derecho which affected a large area of the central United States on June 29, 1998. In the morning, thunderstorms, including a supercell, developed over South Dakota and tracked into central Iowa. As the thunderstorms reached central Iowa, a strong rear-inflow jet developed which caused the thunderstorm to take on a different characteristic, becoming a derecho. It traveled more than 600 miles in about ten hours, causing more than $125 million worth of widespread damage destruction, especially to crops, and was responsible for power outages to nearly a half a million people.
The Tornado outbreak of June 7–8, 1984 was a significant severe weather and tornado event that took place across the central United States from North Dakota to Kansas on June 7–8, 1984. The tornado outbreak produced several significant tornadoes including an F5 tornado which traveled through Barneveld, Wisconsin, in the early hours of June 8, 1984. The entire outbreak killed at least 13 people across three states including 9 in Barneveld alone.
The June 2010 Northern Plains tornado outbreak was one of the most prolific summer tornado outbreaks in the Northern Great Plains of the United States on record. The outbreak began on June 16th, with several tornadoes in South Dakota and Montana. The most intense storms took place the following day across much of eastern North Dakota and much of Minnesota. The system produced 93 tornadoes reported across four states while killing three people in Minnesota. Four of the tornadoes were rated as EF4 on the Enhanced Fujita scale, the most violent tornadoes in a 24-hour period since there were five within 15 hours in the 2008 Super Tuesday tornado outbreak. This was the region's first major tornado outbreak of the year and one of the largest on record in the region, comparable to a similar outbreak in June 1992. The 48 tornadoes that touched down in Minnesota on June 17 marked the most active single day in the state's history. June 17 was the second largest tornado day on record in the meteorological summer, behind the most prolific day of the 2003 South Dakota tornado outbreak on June 24, 2003.
On the morning and early afternoon of June 3, 2020, a powerful derecho crossed Pennsylvania and New Jersey, causing four confirmed fatalities. It was the deadliest derecho in the region since 1950.
On May 12, 2022, a severe squall line followed by a derecho took place across the Midwestern United States. Two fatalities occurred from the first line of storms while three more deaths occurred from the derecho itself.
