Monday, December 18, 2017

Unsettled holiday forecast for southern Quebec

A frozen landscape as sea smoke rises off the St. Lawrence River in Vaudreuil Dorion Sunday morning. The air temperature at the time was -21C (-6F). Milder weather will arrive for a short period this week, before arctic air returns for the holidays. (ValleyWeather Photo)
This will be a busy travel week for many as the Christmas holiday rapidly approaches. Unfortunately, the weather is not going to cooperate with several systems expected to impact the region, along with some dramatic temperature swings. Arctic air is starting to move back into western Canada. This airmass is expected to dive into the deep southern US this week, while at the same time warm air surges north along the eastern seaboard. In between the duelling air masses will be the storm track.

Freezing Rain Possible
A warm front is expected to lift north into our region Monday, with light snow and some freezing rain possible into Tuesday. Accumulations will be light with up to 5cm of snow and perhaps a few millimetres of ice here in Montreal. Eventually the warm air will win out on Tuesday, with the mercury edging above the freezing point to 3C (38F). This warmth will be short-lived, with a sharp cold front arriving on Tuesday night. Temperatures will drop into the lower minus teens by Thursday morning, and remain there into Friday. On Friday, the weather will become quite active once again, with a strong storm developing in western Canada and moving towards Colorado, before moving across the Great Lakes. Several scenarios are in play here, with the exact storm track determining the type and quantity of precipitation. This will not be an easy forecast, but right now we are looking at snow Friday, changing to freezing rain late in the day and perhaps to rain Saturday. The entire mess will freeze up on Christmas Eve day as the arctic air surges back into southern Quebec. To say the least, this type of weather will greatly impact travel across Ontario, Quebec and New England. If you have any travel plans, pay close attention to future forecasts and any warnings as the week progresses.

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