Southwest Ontario Tornado Outbreak of 1984
Encyclopedia
On the evening of September 2 1984 (Labour Day) several tornado
es hit southwestern Ontario
from Windsor
to London
. This was the biggest severe weather
event of the year for the province. During the morning hours, the surface map
revealed a rather potent low pressure system (for late summer) over northern Michigan
, moving to the northeast.
A warm front
was moving into southern Ontario
and bringing with it a moist, unstable airmass
. Thunderstorm
s were also reported across much of district during the early morning hours as well. The cold front
however, was still back over Lake Michigan
and tracking steadily towards the east. During the afternoon, the weather generally cleared up in the outbreak area and temperatures reached the upper 20's Celsius (low 80s F) with dewpoints in the low 20's Celsius (low 70s F).
. A tornado was reported near Lakeport, Michigan (where F3 damage occurred) at around 4:30 pm but continued over the lake as a waterspout
, before weakening. In Ontario, the first tornado touchdowns were near Melrose (just northwest of London) and at Forest
(Lambton County
) at 6:00 and 6:20 pm, respectively. Both of these tornadoes were relatively brief.
The next tornadoes occurred near the towns of Stafa and Sebringville (in northern Perth County
) at around 6:30 and 7:15 pm, respectively. These tornadoes were likely associated with the same thunderstorm (possibly a supercell
, cyclic in nature) as they occurred only within a few kilometres of each other.
At 7:20 pm, the most damaging tornado touched down just southwest of London, where it proceeded to rip through the White Oaks subdivision
at the southern end of the city (not too far from Highway 401
). Approximately 600 homes were damaged and 30 people were injured as a result. Over the northern portion of the city, torrential downpours
dropped 40-60 mm of rain in about an hour and were accompanied by gusty winds. There was one last brief touchdown near Bothwell (northeast of Thamesville
, Kent County
) shortly after the London Tornado lifted.
None of the six tornadoes were assigned official F-scale
ratings by Environment Canada
but the London Tornado was almost certainly significant (F2 or higher intensity).
Tornado
A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...
es hit southwestern Ontario
Southwestern Ontario
Southwestern Ontario is a subregion of Southern Ontario in the Canadian province of Ontario, centred on the city of London. It extends north to south from the Bruce Peninsula on Lake Huron to the Lake Erie shoreline, and east to south-west roughly from Guelph to Windsor. The region had a population...
from Windsor
Windsor, Ontario
Windsor is the southernmost city in Canada and is located in Southwestern Ontario at the western end of the heavily populated Quebec City – Windsor Corridor. It is within Essex County, Ontario, although administratively separated from the county government. Separated by the Detroit River, Windsor...
to London
London, Ontario
London is a city in Southwestern Ontario, Canada, situated along the Quebec City – Windsor Corridor. The city has a population of 352,395, and the metropolitan area has a population of 457,720, according to the 2006 Canadian census; the metro population in 2009 was estimated at 489,274. The city...
. This was the biggest severe weather
Severe weather
Severe weather phenomena are weather conditions that are hazardous to human life and property.- Examples Include :Severe weather can occur under a variety of situations, but three characteristics are generally needed: a temperature or moisture boundary, moisture, and , instability in the...
event of the year for the province. During the morning hours, the surface map
Surface map
In mathematics, geology, and cartography, a surface map is a 2D perspective representation of a 3-dimensional surface.Surface maps usually represent real-world entities such as landforms or the surfaces of objects. They can, however, serve as an abstraction where the third, or even all of the...
revealed a rather potent low pressure system (for late summer) over northern Michigan
Northern Michigan
Northern Michigan, also known as Northern Lower Michigan , is a region of the U.S. state of Michigan...
, moving to the northeast.
A warm front
Warm front
A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient...
was moving into southern Ontario
Southern Ontario
Southern Ontario is a region of the province of Ontario, Canada that lies south of the French River and Algonquin Park. Depending on the inclusion of the Parry Sound and Muskoka districts, its surface area would cover between 14 to 15% of the province. It is the southernmost region of...
and bringing with it a moist, unstable airmass
Airmass
In astronomy, air mass is the optical path length through Earth’s atmosphere for light from a celestial source. As it passes through the atmosphere, light is attenuated by scattering and absorption; the more atmosphere through which it passes, the greater the attenuation. Consequently, celestial...
. Thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
s were also reported across much of district during the early morning hours as well. The cold front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
however, was still back over Lake Michigan
Lake Michigan
Lake Michigan is one of the five Great Lakes of North America and the only one located entirely within the United States. It is the second largest of the Great Lakes by volume and the third largest by surface area, after Lake Superior and Lake Huron...
and tracking steadily towards the east. During the afternoon, the weather generally cleared up in the outbreak area and temperatures reached the upper 20's Celsius (low 80s F) with dewpoints in the low 20's Celsius (low 70s F).
The tornadoes
Towards 4:00 pm the cold front was starting to cross the border and thunderstorms began to form over the southern portion of Lake HuronLake Huron
Lake Huron is one of the five Great Lakes of North America. Hydrologically, it comprises the larger portion of Lake Michigan-Huron. It is bounded on the east by the Canadian province of Ontario and on the west by the state of Michigan in the United States...
. A tornado was reported near Lakeport, Michigan (where F3 damage occurred) at around 4:30 pm but continued over the lake as a waterspout
Waterspout
A waterspout is an intense columnar vortex that occurs over a body of water and is connected to a cumuliform cloud. In the common form, it is a non-supercell tornado over water. While it is often weaker than most of its land counterparts, stronger versions spawned by mesocyclones do occur...
, before weakening. In Ontario, the first tornado touchdowns were near Melrose (just northwest of London) and at Forest
Forest, Ontario
Forest is a small town located near Sarnia, Ontario in Canada. It is very close to the shore of Lake Huron and is part of the municipality of Lambton Shores and the county of Lambton.- Population :...
(Lambton County
Lambton County, Ontario
Lambton County is a census division of the Canadian province of Ontario. The county is located in Southwestern Ontario. It is bordered on the north by Lake Huron, which flows into the St. Clair River, the county's western border and part of the Canada-United States border. To the south is Lake...
) at 6:00 and 6:20 pm, respectively. Both of these tornadoes were relatively brief.
The next tornadoes occurred near the towns of Stafa and Sebringville (in northern Perth County
Perth County, Ontario
Perth County is a census division of the Canadian province of Ontario. The county seat is Stratford and is located in Southwestern Ontario, west of Toronto. It encompasses , 90% of which is classified as prime agricultural land...
) at around 6:30 and 7:15 pm, respectively. These tornadoes were likely associated with the same thunderstorm (possibly a supercell
Supercell
A supercell is a thunderstorm that is characterized by the presence of a mesocyclone: a deep, continuously-rotating updraft. For this reason, these storms are sometimes referred to as rotating thunderstorms...
, cyclic in nature) as they occurred only within a few kilometres of each other.
At 7:20 pm, the most damaging tornado touched down just southwest of London, where it proceeded to rip through the White Oaks subdivision
Subdivision (land)
Subdivision is the act of dividing land into pieces that are easier to sell or otherwise develop, usually via a plat. The former single piece as a whole is then known in the United States as a subdivision...
at the southern end of the city (not too far from Highway 401
Highway 401 (Ontario)
King's Highway 401, also known by its official name as the Macdonald–Cartier Freeway and colloquially as the four-oh-one, is a 400-Series Highway in the Canadian province of Ontario stretching from Windsor to the Quebec border...
). Approximately 600 homes were damaged and 30 people were injured as a result. Over the northern portion of the city, torrential downpours
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
dropped 40-60 mm of rain in about an hour and were accompanied by gusty winds. There was one last brief touchdown near Bothwell (northeast of Thamesville
Thamesville, Ontario
Thamesville is a community in Chatham-Kent, Ontario, Canada. It is located at the junction of former provincial Highways 2 and 21, between Chatham and London. Its name comes from the Thames River that flows nearby and the suffix -ville....
, Kent County
Kent County, Ontario
Kent County, area 2,458 sq km is a historic county in the Canadian province of Ontario. Population in 2006 was 108,589.The county was created in 1792 and named by John Graves Simcoe in honour of the English County. The county is in an alluvial plain between Lake St...
) shortly after the London Tornado lifted.
None of the six tornadoes were assigned official F-scale
Fujita scale
The Fujita scale , or Fujita-Pearson scale, is a scale for rating tornado intensity, based primarily on the damage tornadoes inflict on human-built structures and vegetation...
ratings by Environment Canada
Environment Canada
Environment Canada , legally incorporated as the Department of the Environment under the Department of the Environment Act Environment Canada (EC) (French: Environnement Canada), legally incorporated as the Department of the Environment under the Department of the Environment Act Environment...
but the London Tornado was almost certainly significant (F2 or higher intensity).