A burst of chilly air will reach as far as the swamps of southern Florida next week as a topsy-turvy weather pattern greets the beginning of December. A winding jet stream will allow above-normal temperatures to soar into the Arctic Circle while chillier-than-normal air rushes southward. The pattern will also generate a strong storm system that could bring heavy rain and snow to portions of the eastern United States.
The active weather we’ll experience across the United States and Canada will be the result of an unstable jet stream that’s best described as “flailing willy-nilly.” While that’s not a technical term (though it should be!), it’ll be an interesting setup to start the first week of December.
Jet streams drive most of our large-scale weather patterns around the world. In the northern hemisphere, a trough is a southward dip in the jet stream that’s associated with lower pressure and active weather. Ridges are northward bends in the jet stream that are associated with higher pressure and calmer, warmer conditions.
This week’s jet stream will feature a sharp network of troughs and ridges over North America. A steep ridge over western Canada will allow temperatures to climb above freezing as far north as the Arctic Circle, while a deep trough over the eastern United States brings chilly temperatures and a potent storm system.
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It’s not easy to get relatively warm weather in the Arctic Circle this time of year. After all, the sun is firmly below the horizon there until the latter half of January. If conditions play out as models suggest, temperatures could climb above freezing on Tuesday afternoon deep into the heart of Canada’s Northwest Territories.
As the ridge builds over western Canada, much of the cold air there will begin rushing southward toward the United States. The vast majority of the United States will experience below-freezing temperatures on Wednesday morning, save for a couple of spots around the edges of the country.
The displaced chilly air will extend all the way to southern Florida, where the National Weather Service expects Miami’s low on Wednesday to dip down to 53°F. This would be the city’s chilliest morning since late February, and quite the accomplishment given that this has been Miami’s warmest year on record through November 25.
As we’d expect from such a potent trough, a strong low-pressure system will develop over the eastern United States early next week. It’s still pretty early in the season, so most areas will experience a plain old rain, but just enough cold air will filter into the western side of the storm that some areas—especially around the Great Lakes—could see some snow.
It’s still early to talk about snowfall accumulations, but a couple of inches of snow are possible where the heaviest precipitation sets up. The rain should be more of an annoyance than a problem. Most of the eastern states will see an inch or two of rain through the middle of next week. It’s enough to ruin any outdoor plans, but it could cause some minor flooding issues in areas with poor drainage or where sewer systems are clogged by fallen leaves.