Major freezing rain event forecast for southern Quebec

Freezing rain is rare in April in Montreal, but significant amounts are forecast for Wednesday across southern Quebec.

Freezing rain warning posted for Montreal, southern Quebec and the Ottawa Valley.

It is rare to talk about ice storms in April. The angle of the sun and the warming of the ground usually help to alleviate any significant impacts from frozen precipitation. One thing that can overcome those factors is heavy falling precipitation. We have a situation setting up in the St. Lawrence Valley over the next 48 hours the could create as much as 15-25mm of freezing rain for some locations across southern Quebec.

Clouds are already on the increase Tuesday morning in advance of an elongated warm front stretching from a strong spring storm over Colorado. That low will lift into the western Great lakes, pushing abundant warm, moist air into southern Quebec. Meanwhile high pressure over central Quebec will maintain a cold northeast flow of air at the surface. The result will be a prolonged period of freezing rain on Wednesday, especially along and north of the St. Lawrence Valley.

A swath of significant freezing rain is forecast for Montreal and points north and west of the city on Wednesday. (Environment & Climate Change Canada)

Significant impacts from ice accretion are expected north of Montreal, with up to 25mm possible across the lower Laurentians and northern suburbs. Here in Montreal 10-20 mm is forecast at this time, with the most falling over Laval, and lesser amounts across the South Shore. Over the Eastern Townships and across the St. Lawrence Valley in Ontario, 5-10mm are forecast at this time. Expect difficult travel conditions and  possible power outages on Wednesday. Accompanying the precipitation will be gusty northeast winds up to 50km/h. 

Temperatures will be very mild Tuesday, up to 9C (48F). As northeast winds begin this evening, much colder air will filter into Montreal, with lows of -5C (23F) forecast. The mercury will struggle to reach the freezing point, 0C (32F) on Wednesday.

As the temperature warms above freezing late Wednesday, all precipitation will eventually change to rain. A significant amount of precipitation is expected across the entire region, with total liquid and ice reaching as much as 40mm by the time the storm ends early Thursday morning.

This system is having far reaching effects across eastern North America, including blizzard conditions west of the storm track across the Dakotas and Minnesota and severe thunderstorms south and east of the trailing cold front. As the cold front moves through Ontario and Quebec late Wednesday, a few rumbles of thunder will be possible.

Conditions will improve Thursday and into the long holiday weekend.