Big Chill explained

Wednesday 08th Dec 2010 by theWeather Club

School closures, deep snowdrifts and virtually no transport. The Big Freeze - as present weather conditions are being called - has changed the daily lives of almost everyone in the country. But why is it happening? Ewen McCallum, Met Office Chief Meteorologist, explains some of the reasons behind this intense, prolonged and widespread period of cold weather.

“Normally, our winds come from the west keeping our winters relatively mild. However, during November we have seen a large area of high pressure develop in the Atlantic, causing a ‘block’ to the westerly winds that tend to keep us that little bit milder. As a result this has allowed very cold Arctic air to move south across mainland Europe. At this time of year, the long nights over the landmass of Europe cool down rapidly and so the air has remained bitterly cold. However, this air has had to cross a relatively warm North Sea to get to the UK and has therefore picked up heat and moisture. Because the air is so cold, this has resulted in snow showers forming and with the wind coming from the east, it is coastal areas along the North Sea that have seen the heaviest snow.

"It is very unusual for a period of easterly winds to bring such heavy and prolonged snowfall. In fact for November, the amounts of snow this year have been the heaviest and most widespread in the UK since 1993 and the deepest November snow since 1965. Some of the highest snowfalls at 0900 on 30 November were at Nunraw, Scottish Borders with 44 cm and Kielder Castle, Northumberland with 40 cm. One reason why we have seen such large amounts of snow is that the pressure is much lower than normal allowing the air to rise and form deeper clouds, therefore producing heavier showers.

"This cold spell has produced a provisional UK mean temperature which indicates that this November is likely to be the coldest across the UK since November 1993. There appears to be no abrupt end to this cold and snowy weather for some time.”

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