Here's my best guess at the evolution of things in the coming days: By mid morning wednesday and perhaps a bit earlier, snowfall will initiate from the north and we'll see at least 2" in most areas, up to 5" in the "bullseyes." For whatever it is worth I think Mark Nelsen on KPTV has the right idea in saying there will be a moderation to rain or a rain and snow mix sometime wednesday afternoon as some warmer air comes up from the south. It's a very close call though on how much above freezing we will get.
After the low passes to our north a follow up batch of arctic air will surge south and also via back down through the Gorge. This will fire up snow showers on thursday and I would expect new accumulations, highest wherever some deformation zones set up with banding of showers. This should be a better setup for snow starved Vancouver compared to yesterday.
Friday and saturday look quite cold and there is increasing likelihood of a major storm the second half of the weekend into monday. Some models stall a low off the coast and pump in moisture while continuously drawing out very cold air from the Gorge. As currently depicted on several models this configuration would provide a deep enough cold layer for favoring snow instead of a transition event of sleet and freezing rain. Once the low passes through, you guessed it, probably another reinforcement of cold air.
I put in a graphic down below which analogs to similar upper air patterns seen in the past. Basically we are most likely locked in to this repetitious cold pattern leading up to Christmas day. It remains to be seen if things line up just right for historic snowfalls, but the threat is there.
Be back tomorrow with more........
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