A mid-month temperature shift is about to stir things up across the country
Autumn is a season of transition, so it is common for Canadians to see conditions alternate back and forth between summer-like weather to more winter-like over a short period of time. However, so far the month of October has consistently been in a pattern that has featured warmer than seasonal temperatures over much of eastern Canada and cooler than seasonal temperatures over western Canada. For example, Toronto has had above seasonal high temperatures every day in October, and that streak of above average temperatures extends all the way back to September 25th.
The map below shows the temperature anomalies thus far for the month of October. The various shads of orange highlight the regions that have experienced warmer than seasonal temperatures during October while the blue and green regions have experienced cooler than seasonal temperatures during October.
However, we are now seeing a reversal in the weather pattern with above seasonal temperatures expected in far western Canada and below seasonal temperatures are headed for central and eastern Canada, with the exception of Newfoundland. It also looks like this pattern will lock into place for the rest of October and possibly into the beginning of November.
The following image show one model forecast for October 22 - 26 and the next image shows the forecast for October 27 - 31.
The striking feature is the widespread area of colder than seasonal temperatures that is forecast for much of central and eastern for the end of October. While confidence in long range forecasts such as this is often not very high, there are a number of strong global pattern signals that indicate that at least the general idea shown in the above forecast will actually happen during the next two weeks. So, if you live east of the Rockies you may want to consider a warm costume for Halloween.