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December forecast derailed – will it get back on track?

Friday, December 10th 2021, 6:30 am - The December forecast hasn't quite panned out as expected, thanks to a variety of factors.

What happened to the December forecast? Will we have a white Christmas? These are two very popular questions right now, so let’s chat about both topics since they are related.

First, we will dig into the Good, the Bad and the Ugly of our recent seasonal forecasts and the specific details about December.

I am typically a positive person, so please indulge me as I start off with the good. Our fall forecast called for a warmer than normal season, and that verified very well.

Our winter forecast called for a "come-and-go winter" with above normal temperatures dominating. Of course, it is much too early to grade that forecast, but it appears that we are on the right track so far - especially with the mild weather that is on the way over the next 10 days.


Visit our Complete Guide to Winter 2022 for an in-depth look at the Winter Forecast, tips to plan for it, and much more!


However, that brings us to the bad part of the forecast – which is quickly becoming rather ugly (though many will find the weather to be very pleasant).

Sandwiched in between the forecast for a warm fall and mild winter, we also called for a period of more consistent winter weather for the end of November and for the month of December. That forecast is definitely running off the rails.

We specifically highlighted that the weeks leading up to Christmas would be more conducive to skiing rather than golf. While I don't think many people were golfing this past week, the weather during the next 7 days will be brutal for skiers.

THE SCIENCE BEHIND A BUSTED FORECAST

So, what went wrong?

During mid-November, the jet stream pattern actually changed as we expected it to. However, the impact on the weather down here on the ground where we all live was much less than expected.

The colder jet stream pattern failed to deliver any noteworthy cold air because temperatures across northern Canada were exceptionally warm at the time. So, when cold fronts came through and ushered in air from the north, the best that they could do was to knock our temperatures back down to normal. While that was much colder than what we enjoyed for most of the fall, it sure wasn't very wintry either.

By the end of November, frigid Arctic air was finally in place across northern Canada, ready for delivery. Some of this Arctic air did plunge south into Ontario and Quebec a couple of times, but the bitter cold air lost some of its bite as it travelled across the Great Lakes, which were running at record warm temperatures after such a warm fall (and summer). Nevertheless, it was still cold enough for several significant lake effect snow events.

However, the colder weather has never been able to lock in for more than a few days. The key reason for this unexpected development has been the exceptionally powerful jet stream over the Pacific Ocean which has been pummeling the B.C, coast with a parade of storms and forcing mild Pacific air to spread east across the U.S. and southern Canada. So, each time Arctic air has reached our region, it has been quickly swept away by milder Pacific air.

The image below is the temperature anomaly map for the first nine days of December. Note the various shade of blue and green over most of Ontario and southern Quebec which show that temperatures for the most part were on the cold side of normal.

Early December Temp anomaly

However, temperatures have been well above seasonal just south of the border, especially across the western and central U.S. That mild air surged north into Ontario and Quebec and that will bring an extended stretch of above normal temperatures.

Here is a model forecast for temperatures compared to normal for this past weekend through the middle of this week. The various shades of orange and red across Ontario and Quebec represent temperatures that are much warmer than normal.

Forecasted temperature anomaly

Temperatures through Thursday will be more typical of November and even October.

Meanwhile, frigid weather will continue to build across Alaska and western Canada and the powerful Pacific jet stream will finally take a breather and slow down. This actually gives us a weather pattern across North America that is similar to what we forecast to occur at times during January and February.

So, is this period of mild weather across Ontario and Quebec just an early preview of what we can expect again later in winter, or have we completely bypassed the risk for a period of consistent cold weather during early winter?

WINTRY FOR THE HOLIDAYS? COLDER PATTERN DELAYED BUT NOT DENIED

As we look at how the weather pattern is evolving around the globe, there are actually a number of things happening that are typically precursors to a major pattern change which would result in a more consistent flow of Arctic air rather than Pacific air into Ontario and Quebec.

When will that happen? The pattern change will begin this weekend as temperatures trend closer to seasonal. However, the transition to a colder pattern will likely come in a few back-and-forth steps. As we look ahead to next week, we expect changeable temperatures, but overall, a more wintry week than this week.

That means that a white vs. green Christmas will likely come down to the wire. Several “dominos” will have to fall in just the right way to send us into a period of consistent winter weather for the holidays. Most critical is the change in the jet stream pattern over the Pacific Ocean and into Alaska.

If the pattern develops as expected, that will set the stage for a few weeks of very wintry weather (cold and snowy) between Christmas and New Year’s and continuing well into early January. Here is our preliminary forecast map for the end of 2021 and the start of 2022.

December pattern

However, if the jet stream pattern fails to evolve as expected over the Pacific Ocean, then dust off the golf clubs – mild weather will continue to dominate.

It should become clear by the end of this week whether the forecast will get back on track (and just prove to be off on the timing) or if mild weather will continue to dominate for the rest of winter. Either way, we will post an update, so stay tuned!

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