2:45PM Update: The first round of showers and thunderstorms is over after leaving behind 20mm of rain in metro Montreal. We are now in the warm sector, with very muggy conditions and rapidly rising temperatures. A line of very strong thunderstorms is developing along a cold front in central Ontario. That front will move southeast across eastern Ontario and southern Quebec later this afternoon into the evening hours. Strong thunderstorms are likely. If you have outdoor activities planned for the remainder of the day, stay alert to changing weather conditions and move quickly indoors if threatening weather approaches.
Previous Post: Environment Canada has issued a severe thunderstorm watch for most of southern Quebec. A strong cold front will be crossing the region late this afternoon into the evening hours. The front will cut into a warm and very humid air mass, generating a line or two of strong thunderstorms. The main threat for Montreal will be gusty winds and very heavy rainfall. There is the potential for 25 to 50mm (1-2 inches) of rain in just a few hours. Flash flooding is always a risk with summer storms in Montreal. Warnings will be issued as necessary.
A few showers and a rumble of thunder have already occurred early this morning in Montreal, but the main event will be later this afternoon. In between, expect a few breaks in the cloud cover, along with very muggy conditions and high temperatures from 27C to 30C (81-86F). Conditions will remain muggy overnight and into Friday before the airmass begins to dry out in the afternoon. Lows tonight will be near 20C (68F), with highs Friday near 26C (79F).