The Edmonton Tornado
Reference "Tornado: A Report" by the Alberta Public Safety Services
On the afternoon of Friday, July 31, 1987, a tornado ripped through the eastern part of Edmonton and parts of neighbouring Strathcona County. The tornado remained on the ground for an hour, cutting a path of destruction 40 km (25 miles) long and up to a kilometre wide in places. Wind speeds reached up to 420 km/h (260 mph). The tornado killed 27 people, injured hundreds, destroyed more than 300 homes, and caused more than $330 million in property damage at four major disaster sites. The loss of life, injuries and destruction of property made it the worst natural disaster in Alberta's recent history, and one of the worst in Canada's history.
Tornado Frequencies in Alberta
Although tornadoes are known to have occurred as early as February and as late as November in Alberta, the vast majority have struck in June, July and August, which are the months of most frequent thunderstorms and hailstorms.
The Edmonton Tornado of July 31, 1987
The last week of July 1987 was hot and humid with frequent thunderstorms over much of Alberta. Weather maps were characterized by a weak low-pressure trough over central Alberta at the earth's surface, and a strong flow of air from the southwest at high levels. As the week progressed, surface dew-point temperatures (a measure of the absolute humidity or moisture content of the air) rose to near-record levels at 20 degrees C. Fourteen tornadoes were reported between July 25th and July 30th from Milo in southern Alberta to High Prairie in the north. Most of these highly localized tornadoes were unknown to the Alberta Weather Centre (now known as the NAEnSC) until reported some days or weeks later.
On Friday, July 31, the atmosphere over Alberta continued to exhibit a high potential for severe thunderstorms and associated extremes, such as large hailstones and damaging winds. The 0500 hours forecast for Edmonton predicted an 80% probability of thunderstorms, noting they would be heavy at times. The 1100 hours forecast predicted thunderstorms with hail, damaging winds and heavy downpours. Weatheradio broadcasts and interviews with the media stressed "vicious thunderstorms" and "extremely strong and violent thunderstorms". The assessment of the severe weather meteorologist confirmed the threat of severe thunderstorms. A weather watch commenced. Before noon, a line of thunderstorms developed along the foothills southwest of Calgary, leading to the first "severe weather watch" of the day. These storms intensified and moved rapidly northeastward to reach a line from Ponoka to Sangudo by 1430 hours.
Radar and satellite indicated rapid intensification of the line of thunderstorms as it moved toward Edmonton at 70 km/h (43 mph). A "severe weather warning" was issued at 1445 hours, with as yet no reports of severe events being reported from weather stations or weather watchers. By 1445 hours a new thunderstorm cell developed explosively near Leduc, ahead of the previous line of storms. At 1455 hours a tornado dropped to the ground from this cell briefly and retracted. It struck again near Beaumont as the "Edmonton Tornado" and remained on the ground for an hour over a 40 km (25 mile) path. At 1459 hours, a call reporting a tornado was received, the source being a member of the general public. A tornado warning for Edmonton was issued.
The track damage exhibited rather large variations in width from a few tens of metres up to more than one kilometre. Tornado intensity estimates based on damage observations ranged from F0 (light) near the edge of the track to F4 (devastating) in intermittent patches near the centre of the track.
At least four other tornadoes, including one with intermittent touchdowns between Millet and Vegreville, occurred in Alberta on July 31st. None, however, came close to the duration, intensity and path length of the Edmonton Tornado.
A map of the city of Edmonton showing the path of the tornado.
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