Plunging into winter: Major pattern reversal for November
Monday, October 31, 2016, 8:51 PM - During the fall (and spring), it is easy to lose track of what is "normal" or "seasonal" since that is changing so quickly from week to week.
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October has featured contrasting weather pattern across Canada. Late summer warmth lingered well into October from Ontario to Atlantic Canada (though recent days have been much colder). Meanwhile, below normal temperatures have dominated most of the month across western Canada, including some unusually early and impactful wintry weather.
The map below shows temperatures relative to normal for the first 26 days of October.
As we look ahead to the first week or so of November, we expect that near to above normal temperatures will return to Ontario and Quebec and also expand west to include the Prairies and much of BC. Temperatures across Atlantic Canada are expected to be near normal.
However, it is important to keep in mind that as we head into November, "normal" temperatures continue to fall and swings in temperature will still occur. A couple of days of cooler weather can still readily occur within a period that is dominated by mild weather.
The map below shows the "normal" high temperatures for select cities across the country for November 1st. Of course, there is nothing normal about consistently being at these temperatures during early November. Wild swings in temperature are to be expected during this time of year and “normal” is roughly the midpoint between the contrasting temperatures that we typically experience.
Throughout November, "normal" temperatures continue a steady decline across Canada. The most dramatic decline is found across central regions where seasonal temperatures drop by roughly 10 degrees Celsius during the month. The map below shows the normal high temperatures for select cities on the final day of November.
While we expect temperatures to drop during November, there are signs that the decline will be more profound than usual for parts of the Prairies, Ontario and Quebec. During mid to late November, we expect a pattern change which will bring several rounds of below seasonal temperatures to this region. Meanwhile, near to above seasonal temperatures are expected for British Columbia, the Yukon, and Newfoundland.
When will the pattern change occur?
It is not yet possible to pinpoint the timing for this pattern change, but at this point the most likely timing appears to be sometime during the November 10th to 17th time frame. From time to time, a pattern change like this will occur quite quickly, but more often than not they are slower to develop than expected. Once the pattern change does occur, we expect that it will persist through at least early December.
Get ready for lake effect snow!
Water temperatures in the Great Lakes are running near to above record levels. Therefore, when arctic air does arrive, the contrast in temperature between the lakes and the air crossing the lakes will be greater than what we typically see, and this will help to enhance the threat for substantial lake effect snow squalls in the traditional snow belt areas.
Of course, when talking about weather patterns this far into the future, we have to acknowledge that the pattern might not develop as expected. Many of the long range models maintain mild temperatures for most of Canada right through the end of November. However, we are seeing numerous indications in the global weather pattern that point to this pattern change occurring during mid-November. For the Great Lakes region in particular, this could mean a rather quick transition from a mild fall to impactful winter weather.
Will this pattern change be a false start to winter, or an early start to a long winter season? To answer that question, please check back at 9:00 pm EST on November 21st when we release our forecast for the upcoming winter season.