Polar lows for Christmas

At the end of last year, a cold air outbreak over the Nordic Seas spawned a couple of nice polar lows. This picture was taken on Christmas Day:

xmaspl

The cold air outbreak reached down to Iceland, but there was a boundary-layer cold front, or what we would call an Arctic front, just north of 70 degrees north. These fronts can be nasty in themselves, with strong surface wind speeds and lots of snow, and they also breed polar lows. In the picture above there were two such lows. The only one that developed further, though, was the one on the right.

Here’s a picture taken about 36 hours later:

xmaspl2

By this time the eastern part of the Arctic front has moved south, while the polar low stayed put. The white clouds indicate deep convection, meaning that it had developed tall clouds and probably lots of precipitation. The official meteorological station in Tromsø got 35 mm of snow during 25 and 26 December. Arctic fronts are much more shallow, as testified by the clouds along the one in the picture, but they can easily produce thunderstorms and heavy snow.

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