Heavy rain expected to remain west of Montreal

Montreal lies between two weather systems on Wednesday afternoon, high pressure over Atlantic Canada and a strong upper level low over the Great Lakes. Heavy rain is forecast across Ontario along a slow moving cold front, while Southwestern Quebec will remain relatively dry and very mild for late September.

Summer weather persists across southern Quebec Wednesday afternoon, despite the arrival of fall just a few minutes ago. A slow-moving cold front remains well to our west over central Ontario. That front is the focus for torrential rain and thunderstorms. Widespread rainfall warnings are in effect from the Windsor - Toronto corridor into the Ottawa Valley. Some locations are expecting in excess of 100mm (4 inches) of rain over the next 24 to 36 hours, with flash flooding possible

Meanwhile southern Quebec remains on the east side of the system, with a mild southerly flow, and temperatures well-above normal into the middle 20s. The weather has been exceptionally warm this September, with every daytime high over 20C at Trudeau Airport through Wednesday. This is the first time this has occurred since weather records began in Montreal. The average daytime high through Tuesday has been  22.9C (73F), the normal value should be only 20.6C (69F). We have one more warm day to go before the aforementioned cold front arrives.

The front should begin producing rain and scattered thunderstorms late Thursday into Friday in Montreal. Less rain is expected in southern Quebec as the front will be moving at a faster pace across our region. Expect up to 25mm through Friday morning.

The weekend at this time appears a little more fall-like, with cooler high temperatures expected in the upper teens. A few showers are likely as well by Sunday.