Brief cold snap followed by increasing warmth for Montreal

Graupel fell in Montréal late last Sunday evening as a strong cold front crossed the region. Graupel resembles both hail and snow, but is in a category of it's own. It is often called small hail, typically forming on the edges of the summer season in Montreal during October and April. It is very soft, non-destructive compared to hailstones and usually melts away very quickly.

Temperatures have been on a roller coaster ride this week, with a wide variety of associated weather. Last Sunday evening, we had a strong cold front cross the region, accompanied by thunder, lightning and even some graupel was observed. 

Graupel is often mistaken for hail and indeed has the nickname soft hail. But it often occurs on the edges of the warmer weather here in Montreal, during April and October, when a cold pool of air develops in the upper atmosphere. Graupel is basically a snowflake that has been coated with a supercooled water droplet. This type of frozen precipitation is typically small, less than 5mm in diameter, very soft and non-destructive compared to hail and typically melts very quickly.

The Sunday cold front resulted in a chilly, windy Monday in Montreal, followed by rapidly warming temperatures on Tuesday. The high Tuesday at Trudeau Airport was 19.5C (67F), after an early morning low that was close to the freezing point in many locations along with scattered frost.

The temperatures dropped just as quickly Wednesday morning after another strong cold front crossed the St. Lawrence Valley, falling from 10C (50F) at 9AM to 1C (34F) at 11AM. Along with the colder air came 15mm of rain and even a few snowflakes as the precipitation tapered off.

Looking ahead we have a couple of cold nights on tap to end the week, with sub-zero lows across the entire region, along with frost. Temperatures are expected to warm up considerably this weekend and into next week, with highs exceeding 21C (70F) by Monday. Conditions will be rather unsettled, with the risk of showers over the weekend and even a few thunderstorms next week.