Wet and windy storm to impact southern Quebec

The fall foliage is beginning to peak in the St. Lawrence Valley. The weather this week has been nearly perfect for getting out and enjoying the spectacular colours. That is about to change as windy and wet weather arrives on Thursday. Very cold air will move into our region by next Tuesday, with a few snowflakes possible in many regions. (Valley Weather Photo)

Heavy Rainfall Warning in effect for Montreal

The first significant fall storm of the season is advancing across central Ontario early Thursday, expected to pass well north of Montreal. The cyclone will sweep a strong cold front across the St. Lawrence Valley late this evening. In advance of the front, strong and gusty south winds will develop in Montreal Thursday, gusting up to 60km/h at times. The front will also be accompanied by a wide area of heavy rainfall, expected to start this afternoon in Montreal, and persist into the overnight hours. 

Rainfall amounts of 25 to 50mm are expected in the St. Lawrence Valley, with upwards of 70mm north and east of the city. Some minor flooding may occur, especially where gutters and catch basins are clogged with fallen leaves. Heavy rainfall warning are in effect for most of southern and western Quebec.

As the fall weather patterns become established across Canada, mid-latitude storms become much stronger. This is a result of the large temperature and pressure differences that exist with the changing seasons. An example Thursday morning, we have snow falling across southern Manitoba, with temperatures near 0C, while in southern Quebec, temperatures are already in the upper teens, expected to reach near 21C (70F) along the US border.

The deepening storm system in question will move across northern Quebec tonight, while high pressure builds into the region for Friday and Saturday. Unsettled and much colder weather will return next week, with the chance for more showers along with dropping temperatures. Some parts of eastern Ontario, southern Quebec and New England will see a few snowflakes by next Wednesday.

As far as temperatures are concerned, Thursday will be very mild before the rain begins, pushing close to the 20C (68F) mark here in Montreal. Temperatures will be a little cooler for Friday and Saturday, around 16C (60F). Early next week, high temperatures will drop below normal, into the single digits, with lows near the freezing point.