Last week’s system, which brought significant snow to west-central Manitoba, was originally forecast to travel much farther north. This more southerly route prevented the system from tapping into colder air, which is why we stayed fairly mild. I had also forecast a system to bring snow over the weekend to extreme southern and eastern regions and it too tracked further south, which kept our region in a rather stagnant flow. This resulted in milder-than-expected conditions over the weekend along with fog and some freezing drizzle.
For this forecast period it does look like colder air will finally move in, with temperatures by Friday expected to be right around the mid-December average. What will help bring in the colder air will be a Colorado low, forecast to track through the Dakotas on Wednesday or Thursday. This low is not expected to directly affect our region, but the possibility of some snow can’t be ruled out. As the low tracks to the northeast it will place us in a fairly broad and cool northerly flow.
Arctic high pressure will try to nose southward within this flow, but it looks like the coldest air will remain over northern Manitoba for the weekend before sliding eastwards early next week. Skies look to be sunny to partly cloudy over the weekend and into the early part of next week, with daytime highs in the -6 to -10 C range and overnight lows in the -13 to -18 C range.
This is when things become interesting. The weather models then show a large and strong area of low pressure developing over Montana on Tuesday and tracking along the international border on Wednesday and Thursday. Confidence in this system is very low, but if it does develop, we could see some messy weather just before Christmas, with temperatures ahead of the system warming up enough for rain on Wednesday before transitioning over to snow late in the day. Snow is then forecast for Christmas Eve, with some significant accumulations possible.
Usual temperature range for this period: Highs, -18 to -4 C; lows: -27 to -12 C.