We are starting to see a trend in medium-range weather forecasts this winter. The first half of the forecasts are turning out well but the second halves are struggling.
Last issue’s forecast followed this pattern, with the call for a cold start and then a quick return to milder temperatures. In the second half of the forecast, it looked like mild weather was going to stick around, but thanks to an area of low pressure that came in off the Pacific, that part of the forecast got messed up.
That same area of low pressure is also creating problems for this forecast period. I must create this forecast five days in advance. If the forecast is stable and predictable for those five days, there is not much of a problem, but sometimes (like this time) this is not the case.
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As I write this, the forecast models are still trying to figure out whether our region will get hit by a large Colorado low. Whether we get hit or not, and how hard we get hit, will have an impact on the forecast. As usual when this happens, I will go with what the weather models predict and use this as a reminder that confidence in this forecast is very low.
The weather models are all over the place with this storm system. They have been consistent with the development of the storm, but the track keeps oscillating between hitting southern and eastern regions and missing us to the south.
The potential is there to bring upwards of 20 centimetres of snow. Temperatures will be mild ahead of this low and will then cool rapidly as Arctic high pressure slides southward in the northerly flow behind the low. Expect daytime highs to cool into the -14 to -18 C range by the weekend, with overnight lows falling in the -25 to -30 C range.
This area of high pressure will begin to slide south and east as we begin the week of Dec. 19, so the general flow across our region will become more westerly. This should result in warming temperatures as Pacific air slowly works its way eastward.
Looking toward Christmas weekend, the models hint at another short shot of colder air, but I would not get too worried about that yet.
Usual temperature range for this period: highs-18 to -2 C; lows -27 to -11 C.
