When you study meteorology as a professional weather forecaster, as in most occupations, a lot of time is spent on routine humdrum work, but the subject comes alive when extremes of weather are likely to happen. Sometimes we are too optimistic or too pessimistic because we almost will something exciting to happen. Winter can often be the best time for the forecaster, and more particularly when a Polar Low is likely to form.

Polar Lows or Polar depressions have been called Arctic Hurricanes because they often look very similar to their tropical cousins when seen on a satellite picture, and they also bring some very intense weather. Polar lows are small depressions or cyclones, generally just a few hundred miles across, that form in the cold arctic waters often on the western side of a large decaying depression. Strong northerly winds rush the air southwards, and as it comes over a relatively warm sea, compared with the cold arctic air, it causes the air rise up quickly as convection currents. As this air rises, so it cools and condenses into great sheets of cloud with large cumulonimbus clouds embedded in it, and if you look at this cloud pattern on a satellite picture it has a similar look to a tropical hurricane, even with the eye in the middle.

The whole system is quite small, and because of the scarcity of weather observations in this arctic region, weather forecasting computers have great difficulty in predicting where they are likely to go. Because of the time of year much of the precipitation from these polar lows is in the form of snow, and as they move rapidly down from the north and reach landfall over the northern parts of the British Isles, we end up with heavy falls of snow and gale force winds giving blizzard conditions. The whole system dies out very quickly once it comes inland as the supply of the relatively warm water is cut off, in fact the whole life cycle of this 'arctic hurricane' from birth to mature stage and decaying may only last one or two days.

So during this coming winter look at the weather map on television, and try and spot a strong northerly blast of air coming down towards the country, and if the isobars show a distinct wiggle in the pattern to the north of Scotland, think Polar Low. At the same time look at the Presenter's face, because if there is a possibility of a polar low, they will be looking very excited too!