Monday, January 08, 2018

Thaw equals relief from the bitter cold for Montreal

Warmer air is trying to push into Montreal this week. Before then, we can expect a messy mix of snow and perhaps freezing rain. The mild air will be pushed out of the region by Saturday. (ValleyWX Photo)
What a difference a few hours can make in weather forecasting and observations. If you would have asked me just a few days ago if I thought we were going to have a thaw this month, I would have likely said no. Yet here we are, just a couple of days away from a forecast high of 8C (47F) in Montreal. The first phase of this thaw will persist for about 48 hours in Montreal. I expect it will be a difficult transition to above freezing temperatures, as the ground is so cold, along with a very firmly packed snow base.

Before we look at the future, let's just take a quick peak at the recent weekend cold snap. If you thought the weather was brutal Friday and Saturday in Montreal, it was. Strong low pressure moving across Atlantic Canada, relentlessly pushed gusty north winds and biting cold into southern Quebec. At Trudeau Airport, the wind gusted over 50km/h (31 mph) for nearly 42 consecutive hours from January 4th to the 6th. At the same time, plummeting temperatures produced wind chills colder than -30C (-22F) for 53 consecutive hours. The peak wind gust measured was 70km/h, with the coldest windchill -40C. The wind, combined with 10cm of fresh falling and blowing snow, produced visibility under a few kilometres for several days. Near blizzard conditions were observed at times on the flat farmland south of Montreal towards the US border, from early Friday into Saturday morning.

January Thaw
Our much anticipated January thaw will come in two parts, the first this week, and another mild stretch around the 20th. A surge of warm air is arriving today on southwest winds. The initial warm air advection is producing a moderate snowfall of 10 to 15cm in the St. Lawrence Valley. The temperatures will continue to warm this week, rising above the freezing point by Thursday. The milder weather will come with more precipitation, in the form of freezing rain and rain late Wednesday and Thursday. By Friday night, colder air will return, along with a transition from rain to snow in Montreal. Saturday could be quite stormy, as another system approaches from the US southwest. By the weekend, temperatures will fall back to more normal values which are -6C/-15C. If you have travel plans late Friday and Saturday, you will want to play close attention to updated forecasts later this week.

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