Tuesday, November 30, 2010

"North Sea Effect": UK November Snow Deepest Since 1965;
Widespread Travel Disruption

Dec. 1 Update: The November 26-30 average sea level pressure shows an excess of more than 35 mb between Greenland and Iceland along with a deficit of 15-20 mb over central Europe. This intensifies the easterly and northeasterly air flow over the UK. The accompanying map of average wind speed and direction shows the strongest winds over the North Sea and to the north and west of the British Isles and Ireland.

The BBC reports (Snow and ice causes disruption as cold spell continues) this evening:
Temperatures are set to plunge again overnight after one of the coldest starts to December in more than 20 years has caused chaos across the UK.

Some 4,000 schools have been closed, and Edinburgh and Gatwick airports will be shut until at least Thursday.
Images (click to enlarge): View of Gatwick Airport from BBC; 5-day average sea-level pressure and winds for November 26-30 from NOAA/NCEP operational data

Original post:
The Met Office has announced that the recent UK snow is the deepest since 1965. Ewen McCallum, the Chief Meteorologist, explained the atmospheric circulation patterns causing the intense early season cold and snowfall:
Normally, our winds come from the west keeping our winters relatively mild. However, during November (like last winter) 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. The localised nature of showers means that the amount of lying snow has varied greatly from place to place.
The BBC reports:
Hundreds of schools have closed, driving conditions have been hazardous, and rail and air passengers have been delayed, as the snow moves south.

The Met Office has issued heavy snow warnings for Yorkshire and Humber, east Midlands, east and north-east England, London and south-east England.
The surface/500 mb pressure chart (rotated for clarity) shows very strong high pressure extending from south of Greenland eastward to Scandinavia. Easterly flow to the south is bringing cold air from the European continent westward across the UK.

Other coverage:

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