Weatherwatch: polar low, the blizzard-inducing phenomenon

PAGolar lows are vigorous, short lived, mesoscale atmospheric low pressure systems. Normally between 300-800km in horizontal extent, they typically last no more than 48 horas. A winter phenomenon, these lows can bring strong winds and heavy snow, leading to blizzard-like conditions. They form in polar or Arctic maritime airstreams over high-latitude ocean basins: most common formation areas are the Norwegian Sea, the waters around Iceland and the northeast Atlantic.

There are different types of polar lows, each forming in slightly different ways, but the main the main mechanism behind their existence is horizontal differences or gradients in temperature.

During the winter, the air over the ice-covered Arctic regions becomes very cold, while the adjacent sea surface temperature could be 20-30C warmer. As the cold air moves over warmer seas, it causes convection as the unstable air rises to form cumulus and cumulonimbus clouds, thus creating low air pressure at the surface. The cloud wraps around into a tight circulation around the rapid deepening low pressure centre. As the polar low develops, it forms a comma-shaped cloud feature and then, in its mature stage, a clear central “eye” forms.

These characteristics are not dissimilar to tropical storms, which form at lower latitudes, so polar lows are sometimes referred to as “Arctic hurricanes”.

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