October ended up to be about normal in terms of temperature despite the chilly last couple of weeks. In fact, 14 of the last 17 days of the month were at or below normal. A natural question arises in the face of this cool spell — namely, does this portend a cold start to the winter?
The official November-January forecast from the Climate Prediction Center of the National Centers for Environmental Prediction (NCEP) gives us a slight probability of above-average temperatures for the next three months and even chances for normal amounts of precipitation over that interval. This forecast may arise from the fact that sea-surface temperatures in the central tropical Pacific Ocean are nearly normal heading into the cold season.
Our own harbinger of the early winter focuses on the presence or absence of snow cover in northwestern Canada. The idea is that if there is snow cover there by mid-late October, the chances of producing cold air masses there increase as the daylight hours decrease in late fall. Cold air produced in northwest Canada is often involved in our early season cold air outbreaks.
We are testing this idea in current research. So far this year, there has been unusual warmth (and consequently little snow) in northwest Canada. Thus, our prediction is in line with that of NCEP — the early part of the winter will not be memorably cold.