These three obstacles can stop an Arctic air invasion
Frigid air spilling out of the Arctic is a powerful force, and only a handful of natural features can stop that chill in its tracks
If you’re one of the many Canadians and Americans who dread winter, you probably spend a lot of time being jealous of the warmth in the south and fearing the frigid air in the north.
Every so often, that Arctic air wants a southern vacation and heads south across North America. When this happens, where’s the best place to hide if you want to avoid the freeze?
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In Canada, there are only two hiding spots, both of which can still leave you vulnerable.
The Rocky and Coast mountain ranges in British Columbia can dam the bulk of the Arctic air, slowing its progression to the Pacific coast. If the Arctic air is in place long enough, it will eventually seep through the mountains, resulting in Arctic outflow.
The other place to hide is southern Ontario. Mountains won’t protect you here, but the Great Lakes can act as a pretty effective defense. Arctic air usually flows from the Canadian Prairies, having to cross as much as 700km of water before reaching southern Ontario.
The lakes can be more than 30°C warmer than the air at times, which takes a big bite out of the chill. From when the air first meets the lakes, it can be warmed as much as 20°C by the time it reaches Toronto.
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In the U.S., the mountains in the west play the same role as in B.C. In the central Plains, Arctic air is free to flood south without any interaction with mountains or lakes. This unimpeded flow can result in sub-freezing air reaching the Gulf of Mexico.
The East Coast has its own guard, even when the Arctic air avoids the Great Lakes. The Appalachian Mountains are quite underwhelming compared to the Rockies, but they are quite efficient at blocking an Arctic cold front.
The spine of the Appalachians through Tennessee, the Carolinas and the Virginias are higher than 1500m. This elevation can prevent the core of dense arctic air at the surface from spilling east toward the Atlantic coast.
However, just like the west coast, if the cold air is in place long enough or the layer is deep enough, it can build up like water behind a dam until it reaches the low points in the mountains.
The cold air rushes through the gaps and accelerates as it descends into the lower lands east of the mountains. This leads to streams of cold air east of the mountains while a pool of colder air remains on the western slopes.
Header image courtesy of Gary Yost/Unsplash.
