Heat warning in effect for Montreal and Ottawa

Thunderstorms on Saturday afternoon across portions of southern Quebec only helped increase the humidity across the city. The warmest day of the current heatwave is forecast on Monday, with a high of 34C for Montreal. Overnight lows will remain sultry, dropping to 24C (76F).

Widespread heat warnings are in effect for southern Quebec including metro Montreal, eastern Ontario, including Ottawa and the Champlain Valley of New York and Vermont. The combination of very warm temperatures and elevated humidity will make it feel closer to 40C today. Drink plenty of water and relax outdoor activities when possible. Dry to spend a portion of the day in air conditioned space. Montreal is already at 23C (73F) at 6am.

Monday will be the warmest day of the current heatwave, with high temperatures expected into the middle 30s across portions of southern Quebec, along with high humidity. We can expect a record-breaking high of 34C (94F) in Montreal, which should surpass the previous benchmark of 33.4C set in 1999. Gusty winds are also expected today from the southwest 30 to 50km/h, helping to pull in tropical air from the Gulf of Mexico.

On Sunday, the heat and humidity built up quickly after the afternoon thunderstorms on Saturday. The high was 31.4C (89F) in Montreal, also a record for the date beating the 2005 high of 30.8C (87F). The storms on Saturday became rather strong for portions of the city, with close to 15mm of rain falling in less than 30 minutes at Trudeau Airport. Locally, some parts of Montreal received over 30mm, but I only measured 4mm here on Ile Perrot, as the storms passed northeast of my location. Strong winds were observed as well, along with frequent lightning. 

Monday should be dry for most of us, with just a slight risk of a shower or storm in the mountains well north and southeast of the St. Lawrence Valley. Showers and thunderstorms will increase on Tuesday ahead of a backdoor cold front. That front will cross the region early Wednesday, ushering in drier and slightly cooler air. Before then, expect a hot day Monday and Tuesday. The high on Tuesday will be near 31C, dropping to 30C for Wednesday. Overnight lows will be very warm, in the low to middle 20s in Montreal. Much cooler, more pleasant air arrives for Thursday, with a high of  24C (76F) forecast and lower humidity.