Major winter storm to impact region after brief thaw

Freezing rain warning in effect for Montreal and Ottawa today and tonight.

Frozen in time. A much needed thaw will begin in Montreal on Thursday, but end just as quickly on Friday. A potent storm system arrives for Saturday, with heavy snow expected. (ValleyWeather Photo)

Temperatures are on the rise today as clouds increase across southern Quebec. A warm front will approach the St. Lawrence Valley this afternoon and overnight along with an increase in moisture. Light freezing rain is forecast to start in eastern Ontario late this afternoon, and move into Montreal by the middle of the evening. The precipitation will be light, perhaps 1-4mm, but any freezing rain can be problematic on the roads. As the temperature continues to rise overnight, up and above the freezing point, any frozen precipitation will taper to a few showers. On Thursday, gusty southerly winds will allow for the temperature to climb to near record levels, between 5C (41F) and 10C (50F) in southern Quebec. The record for Montreal is 9.4C set in 1975.

The commute this week in Montreal has been slow and painful at times. The extremely cold weather has been slow to moderate, making roads snow covered and slick. (ValleyWeather Photo)

Major Winter Storm
By Friday, a strong arctic boundary will move across Ontario into southern Quebec by the supper hour, bringing a quick end to our thaw. Expect steady rain to develop in Montreal ahead of the front, along with very mild temperatures to start to the day. As the front moves south of Montreal, the mercury will drop quickly, from a high of 6C (43F), down to -7C (19F) by Saturday morning. Any precipitation will change to freezing rain and eventually snow from west to east. How much of each type of precipitation has yet to be determined, but it will be significant. The front will stall across central New England on Saturday, with deepening low pressure moving along it. Freezing rain and snow will continue all day Saturday, with blowing snow and dropping temperatures. My current thinking is 10 to 20mm of rain will fall on Friday, followed by 15 to 25cm of snow overnight into Saturday. This is subject to change as the track of the low pressure becomes more clear. Due to the nature of this event, amounts could vary significantly by region, depending on your local temperature and how fast the changeover occurs. The mess will freeze solid over the weekend, as temperatures drop back to below normal values. Skies will slowly clear Sunday, with a daytime high of only -12C (10F).