From Heat Waves to Tornadoes
The first heat wave this summer may have prompted some people, especially those without easy access to air conditioning, for a return to cooler times. A warm and humid air mass invaded Northwestern Ontario (NWO) and adjacent areas in the American Midwest last weekend.
Various warnings were issued by Environment Canada for excessive heat during the weekend for the entire NWO area. Actual temperatures and Humidex readings on Monday confirmed this advisory. In Thunder Bay, the temperature reached 33.2° C (92° F) with a top Humidex (feels-like temperature) of 41 (105° F). Other locations may have felt “cooler”, for example: a Humidex in Fort Frances and Atikokan of 39 (102° F), Nipigon was 36 (96° F), and 34 (94° F) in Armstrong.
In addition to the heat, the weekend weather prompted another level of weather warnings. A favourable environment of hot and humid conditions combined with potentially large convective systems (a mesocyclone) created the possibility for tornadoes in parts of the region; Fort Frances, Red Lake and Armstrong. In meteorological terms, a tornado is a rapidly-rotating column of air associated with a cumulonimbus cloud that reaches the Earth’s surface. Tornado formation is complex and requires considerable atmospheric moisture, instability, and both wind speed shear (higher wind speeds with altitude) and directional wind shear. Thankfully, less than 30 % of strong mesocyclones produce a tornado.
The heatwave was destined to end abruptly in the early hours of Tuesday with a fast-moving frontal system and this process prompted warnings of heavy rain, damaging winds (strong gusts) and intense lightning. Such predictions are difficult to verify because rain amounts and peak winds vary greatly. However, 39 mm of rain within a 25 minute period was recorded at the Thunder Bay Airport. Armstrong received 70 mm of rain early Tuesday morning
Weather Outlook: Mainly sunny with seasonal temperatures, and very occasional showers. Clear overnight.