Another round of heavy rain forecast for southern Quebec

Another round of heavy rain is expected across the Montreal region during the morning commute on Friday. While excessive amounts of rain are possible, we are not expecting any severe weather at this time.

Environment Canada has posted a special weather statement for southern Quebec including metro Montreal, for the overnight period into Friday morning. Another round of heavy rain along with embedded thunderstorms is expected to drop 30 to 50mm (1-2 inches) of rain across the region, with more possible in the most persistent storms. Some flash flooding is likely once again.

Thursday will be the best day of the week, expect mostly sunny skies, with a warm high of 28C (83F). Clouds will be on the increase this evening, as low pressure over Michigan moves northeast to lie near Cornwall, Ontario early Friday morning, and Quebec City by late in the day. Thunderstorms will develop during the pre-dawn hours, moving through Montreal during the morning commute. At this time I am not expecting any severe weather (strong winds, hail), just heavy rain. Some flash flooding is possible, along with ponding of water on area roadways. There will be a break in the rain mid-morning, with more precipitation developing during the afternoon hours.

Isolated thunderstorms during the afternoon will bring the threat for more heavy rain. Showers will persist into Saturday before skies begin to clear out late in the day. Temperatures will be cooler on Friday along with the clouds and precipitation, with a high of 22C (72F) expected. The highs over the weekend will be around 26C (79F), with lows of 18C (65F).

Waterways across all of southern Quebec are running high at this time, and the ground is saturated in many locations. Lac Memphremagog in the Eastern Townships, southward into northeast Vermont was under a flood warning on Wednesday, responding to the copious amounts of rain that has fallen in that region over the last week. 

July has been excessively wet across our all of southern Quebec, northern New York and New England. Montreal, Trudeau Airport has measured 106.8mm of rain through Wednesday. Other locations across the metro region have received even more, well in excess of 150mm. Meanwhile, 225.4mm has already fallen in Sherbrooke since July 1st, with 202.6mm in Quebec City, 141mm in Trois-Rivieres and 108mm in Vaudreuil-Dorion.

There is some good news in the forecast, the blocking pattern that has kept us so wet this month is showing some signs of relaxing it's grip next week. While the week will not be entirely dry, there will be a decent stretch of sunny, warm weather with precipitation finally at or slightly below normal for the week.

First two Quebec tornadoes of 2023

One final note, the Northern Tornadoes Project from Western University in Ontario has concluded its investigation into last Thursday's severe weather.  They determined that 6 tornadoes occurred along with 5 significant wind downbursts during the severe weather outbreak July 13 across Ontario and Quebec. In Quebec, two tornadoes occurred, both rated as EF-0, with estimated winds of 130km/h. One was reported near Saint-Thomas with second observed close to Mirabel Airport. Other storms produced hail and flash flooding in Montreal and Laval along with widespread tree damage and power outages.