All-time records at risk as Prairies feel major U.S. heat dome
All eyes are on a heat dome building south of the border, which will push extreme heat into the southern Prairies into next week
A multi-day extreme heat event building over the United States will extend its influence into Canada, roasting portions of the Prairies with excessive temperatures and humidity levels.
Some all-time temperature and humidex records are at risk of falling on both sides of the border.
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Major heat building through the middle of July
We’re watching a significant ridge of high pressure, known as a heat dome, building over the north-central United States.
This powerful ridge will send temperatures soaring toward record territory into next week, with scorching heat in the forecast for the Prairies on Sunday and Monday.
Heat warnings are widespread across the region, where readings in southern portions of Saskatchewan and Manitoba will easily climb into the middle to upper 30s. Sunday’s high of 38°C in Winnipeg would make it one of the city’s hottest July days on record.
Folks across northwestern Ontario will get into the heat and humidity as well, with highs of 36-37 degrees forecast for Thunder Bay, Fort Frances, and Dryden.
A cold front will slide across Saskatchewan on Monday and allow temperatures to fall, but another day of excessive temperatures is forecast for southern Manitoba.
Very high humidex values in the forecast
This will not be a dry heat, which increases the potential for heat-related illnesses in vulnerable people. Humidity prevents sweat from evaporating efficiently, precluding our ability to cool off without air conditioning.
Humidex values in the upper 40s to near 50 would approach all-time records in southern Manitoba.
The highest humidex ever observed in Winnipeg was 47.3 on June 25, 2007. This event could exceed that sweltering mark. Canada’s all-time humidex record was 52.5 set on the same day in Carman, Manitoba.
Forecasters are closely watching the potential for record warm overnight lows, as well. Folks without access to air conditioning rely on cooler nights to find relief from extreme heat. Winnipeg’s warmest overnight low on record was 28.3°C on July 12, 1936.
Searing temperatures are also in the forecast for the north-central U.S., where readings will easily exceed 40°C not far from the border. Billings, Montana, may hit 43.3°C (110°F) on Sunday, which would be the city’s hottest temperature ever observed.