They say a picture is worth a thousand words. Here is a nice picture of how the snow pack is spreading, compared to normal for this time of year:
The purple shows where snow cover is expanding greater than climatology. The red shows where there is a lack of snow cover in comparison to normal. You can see that snow cover is expanding at a prolific rate over Siberia while snow cover is having a difficult time getting a toe-hold over Canada.
Why?
Though October so far, the prevailing weather pattern has not allowed for a significant buildup of cold air over Canada. This is also the reason that it’s been warm here.
What’s Going to Change?
I’m so glad that you asked. 🙂
A significant pattern shift is expected to occur over the next 1-2 weeks. The North Atlantic Oscillation will plunge to its negative phase (NAO-) while a high amplitude ridge develops over western Canada into Alaska as a manifestation of the positive phase of the Pacific North American Oscillation (PNA+). This high latitude blocking pattern would allow the Canadian Polar Vortex to set up shop near Hudson’s Bay for the first time this autumn:
True arctic cold air from Siberia would spill over the North Pole and be driven into the heart of Canada during the final two weeks of October. This would result in rapid buildup of snow cover over northern Canada and introduce the cold shots into the northeastern United States that we have lacked so far this month. Having the Canadian Polar Vortex that far south would have no difficulty in sparking a lake effect snow event before the end of October. Perhaps we can have some snow on that Halloween pumpkin!
Not to be lost in the commotion is the westward migration of the Siberian Polar Vortex, which should spread snow cover into northeastern Europe, ahead of climatological schedule. Remember, a rapid spread of Eurasian snow cover in October can be a good sign for snow and cold in ilsnow land in the winter.
Darrin @ ilsnow.com
