Heat warning for Montreal - followed by fall-like stretch of weather to begin August

A towering thunderstorm over Pincourt last Thursday, July 13. The storm produced torrential rain, but thankfully was quick moving, alleviating the flood risk. More strong storms are possible this Thursday and again next Tuesday, before much cooler weather arrives to start the month of August in Montreal. (Valley Weather Photo)

Environment Canada has issued a heat warning for southern Quebec for Thursday, with high temperatures expected well into the 30s, and humidex readings approaching 40C (104F) in Montreal during the afternoon hours.

The hot weather is part of an expanding heat dome that has resulted in widespread weather warnings across a large portion of the central and eastern United States and into southern Canada. Along the circumference of that heat dome, heavy thunderstorms have been occurring through the Dakotas, upper Midwest and Great Lakes into parts of Ontario.

For Montreal, we can expect a very warm and humid Thursday, with a forecast high of 33C (91F). Clouds will increase late in the day as a cold front advances into the St. Lawrence Valley from central Ontario. Showers and thunderstorms are likely, persisting into Friday. Some may be on the stronger side, with heavy rain and gusty winds possible.

Friday will be a little cooler, with daytime highs in the middle 20s. The heat will build again Saturday though Monday, with highs once again near 30C (86F). Overnight lows will be in the upper teens to near 20C.

By Tuesday, a more potent cold front will result in another round of showers and thunderstorms. Finally high pressure moves into southern Quebec to end the month and start August, with much cooler weather expected. Highs will drop into the lower to middle 20s for many locations, with overnight lows in the lower teens and even some single digits. The early taste of Autumn for Montreal will prevail during the first week or so of August.