UK Snow Prediction Problems

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Snow always seems to create problems for the United Kingdom, far more than in other European countries. This page makes some suggestions why this is the case.

Some thoughts on snow in the UK

Fairly obviously it is disappointing that the various transport authorities seemed as insufficiently prepared for the snow during December 1010 as they were last February and during February 2009. On each occasion the snow was commendably well predicted. One of the more impressive aspects of forecasting over the recent year or so has been the ability to predict severe or extreme weather over fairly small areas. This is because of the continuing effort by meteorologists, the UK Met Office in our case, to maximise use of weather data, especially from satellites, and increased computer power. One of the imperatives for the development of detailed short period forecasts is the need to be able to warn of such events as the Boscastle storm.

However, and regardless of the excellent forecasts, snow in Britain creates more problems than elsewhere in Europe and results in widespread public criticism and anger. Partly, of course, the UK, historically, has had less snow than our continental neighbours and has less investment in equipment that may never be required during its design lifetime. Partly and, I believe, largely overlooked is the fact that “our snow” can be different.

Are there really different kinds of snow?

Snow events can be categorised into three types. First, these are, from Atlantic weather systems coming up against cold low level, often dry continental air, secondly, showers, troughs of low pressure or fronts coming from the east; thirdly, snow showers in northerly airstreams. I will look at these in turn.

Atlantic lows, such as we have had during December 2010, have some quite warm and moist air at levels where the precipitation is formed. Much of our rain from Atlantic lows, in general, starts as snow but melts on the way down. So, although it may start to rain at ground level, rain falling through cold dry air evaporates so cooling the air further and the rain can turn to snow. On other occasions, of course, the snow never melts. In either case, because of where the air has come from, the snow has a high water content and can be difficult to clear. By the time these systems have crossed the British Isles and reached the continent, they have lost much of their water and snow may well be less intense. During this December period some of the snow over France and the Low Countries was still fairly heavy but less so than over the British Isles.

Showers or more organised areas of winter precipitation coming westwards across the North Sea are a different matter. Because the air will be fairly dry, with a long continental history, amounts of snow over the continent may not be great. However, The North Sea is comparatively warm, maybe 6 or 7 degrees Celsius in December falling to about 5 degrees in February. This has the effect that air crossing the North Sea can pick up more water vapour resulting in greater falls of snow than over our European mainland neighbours. It is likely that the snow would be heavier and wetter than might have occurred over the continent.

Snow showers in northerly air streams can be quite heave wherever they occur but will be more so around North Sea Coasts exposed to that direction. There seems to be no reason why such showers should be a greater problem to the UK than to NW Germany or the Low Countries.

Cab we plan for it?

Whether such severe weather is going to be more likely than in the past is uncertain. I do not know whether the Climate experts at the UK Met Office Hadley Centre can quantify the risk well enough for planning purposes. However, it is fair to say that one of the, well publicised, expected consequences of global warming is that weather extremes will become more likely.

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