Sweltering heatwave forecast by Canada Day for Ontario and Quebec

The first heatwave of the season should arrive in Montreal by the end of the week. High temperatures are expected to reach the middle 30s. (AccuWeather.com)

The first heatwave of the summer is anticipated by the end of this week, with record setting temperatures quite likely. Montreal can expect sunshine and warmer temperatures on Tuesday, with a high reaching 25C (77F). On Wednesday, low pressure and a warm front will approach form the Great Lakes, with a period of showers and isolated thunderstorms expected through Thursday afternoon. Rainfall amounts may approach 25mm (1 inch) is several locations across southern Quebec. The temperatures will remain mild despite the clouds and rain, with highs generally in the middle 20s.

Record Setting Heatwave

The passing warm front will set the stage for what could be a record setting heatwave across a large portion of eastern North America. Strong, warm high pressure will surge into the Ohio Valley and slowly move across the northeastern US through the Canada Day/ July 4th holiday period. The temperature will rise above 21C (70F) early Thursday morning in Montreal, and likely not fall below again until late Tuesday night. During this time, warm southwest winds will drive high temperatures into the low to mid-30s. By Sunday, the high may reach 37C (99F) in Montreal and Ottawa. Combined with building humidity, several cities may see humidex values as high as 45C (113F). The heat will surge into southern Ontario by Thursday, reaching Montreal and southern Quebec Friday. High temperatures across a wide portion of the region will reach between 35 and 37C (95 to 100F). 

As far as records go, the highest officially recorded temperature in Montreal was 37.6C (99.7F) set on August 1, 1975. In Ottawa, 37.8C (100F), set on August 11, 1944. During the 1975 heatwave in Montreal, several urban locations did rise above the 100F mark. The feeling is that several locations in southern Quebec and Ontario, may approach the 100F mark on July 1st. Whether we break the century mark or not, it will be dangerously hot. Heat advisories will likely be needed. Urban areas without air conditioning, will become unbearable by the end of the weekend. It is important during high heat events to remain hydrated and avoid over exertion. Be extremely vigilant when it comes to pets and children, especially around hot cars. Be sure to check on elderly relatives or neighbours.