Rare November thunderstorms followed by snow

A few rare nocturnal November thunderstorms developed in advance of a cold front early Tuesday morning across the Montreal region. Much colder air and more snow is on the way by Thursday.

Much colder air arrives in Montreal later today, followed by up to 5cm of wet snow Thursday.

Montreal had a few surprise thunderstorms during the pre-dawn hours Tuesday, along with viid lightning and some heavy but very brief rainfall. The culprit is a clipper-type low pressure system and cold front over the Ottawa Valley, slicing southeast into some moderately unstable air. Temperatures are quite warm this morning, around 10C (50F) here on Ile Perrot. This will likely be the high for the day, as cooler air begins to filter into the St. Lawrence Valley later this morning on gusty northwest winds of up to 50km/h.

Temperatures will fall all day, down to below freezing this evening at -1C (30F) in Montreal. Wednesday will be partly sunny, but breezy and much cooler, with a high of only 3C (38F). That cooler air will set the stage for some mixed precipitation across eastern Ontario and western Quebec starting during the overnight hours into Thursday morning. Another Alberta Clipper will slide across the Great Lakes and St. Lawrence Valley bringing a swath of snow and rain to the region.

The temperature will be marginally cold enough in Montreal for snow to start, likely mixing with and changing to rain at some point Thursday. At this time, up to 5cm of wet snow may fall in several regions of southern Quebec, more to the north of the city and less south towards the US border.

There are still some details to work out, and this will not be a big storm by any stretch. However, November snowfalls can be very tricky and certainly can make driving challenging. Allow extra time for the Thursday morning commute.