Snow on Campus Pictures - Greenspan (FINAL) - 21-11-29-3.jpg

Students walk to class to prepare for the end of the term outside Talbot College, one of Western University's music buildings amid a fresh snowfall. 

With the Christmas season quickly approaching, one of the most common questions on everyone’s minds is whether or not this year will be a white one. 

How we predict whether or not there’ll be a white Christmas has to do with a variety of factors, from the air and atmosphere above us to temperatures in the Pacific ocean. Meteorologists can use computer models to make ground observations and look at the depths of the atmosphere, and satellite imagery can also be used to take in the current state of the atmosphere and see how it evolves.

But these methods aren't perfect, as James Voogt, a professor in Western University’s geography and environment department, points out. 

“The initial conditions we know for the atmosphere are never perfect,” he explains. “There’s always airs and conditions in our pictures that we would initiate a model with but the predictability drops off. After seven to 10 days, we don’t have a lot of predictability in the weather.” 

Environment Canada has a two-week forecast where they can tell if the temperature will be above or below normal by looking at larger scale patterns of warming and cooling, as well as the positions of jet streams in the ocean. The success of different prediction methods also depends on what exactly you’re trying to predict. Trying to predict the average weather for a 10-day forecast is much easier than trying to track an individual thunderstorm or blizzard. 

Predicting long-term weather, like what it will be like in late December, gets more complicated. If meteorologists attempt to predict past the seven to 10-day limit, “chaos takes over,” says Voogt. 

One way meteorologists can specifically predict white Christmases is by looking at the average number of white Christmases in a certain area. For example, places in Northern Canada like Algonquin or Northern Alberta might have had more white Christmases in the past. Based on this, one could predict that this year might also be a white Christmas. 

London only has about a 55 per cent chance of this Christmas being snowy according to Environment Canada. This percentage has also significantly decreased due to climate change — 40 years ago, London had an 80 per cent chance.

Natural forces also factor into this Christmas’ weather in London, mostly revolving around the Great Lakes. Because of London’s proximity, we actually have a decreased chance of a white Christmas. 

“The Great Lakes in the early winter will keep places like London warmer than they would otherwise be. Downwind of the Great Lakes is where the climate is moderate in the early winter, acting to reduce the frequency of white Christmases,” says Voogt.

Whether you want this holiday season to be snowy or not, it still seems to be up in the air — or atmosphere — for now!



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