Winter Storm – December 2013 (5th to 6th December)
Summary
On 5th December 2013 a depression passed over the UK due to the Polar Jet stream being unusually for south. This caused the wettest December since 1776, with a series of low pressure weather systems bringing some characteristic storm events. However it was the storm event on the 5th of December that had the heaviest impact according to the Met Office.
Causes
The synoptic chart (left) shows the meteorological basis of the storm. At 1200 UTC a deep area of low pressure can be seen moving south-west across the UK; it can be seen just off the north-east coast of the UK at a pressure of 967 millibars. This alongside other oncoming depressions would (as well as bringing heavy stormy weather) cause a storm surge affecting the North Wales and North Sea coastline.
Unlike the formation of depressions off the west coast of the UK, this depression was formed from Polar Maritime air, from Greenland, and Tropical Maritime air, from the Azores, however as it had been moved North by the Polar Jet Stream it had picked up much more moisture than any typical depression, however it had also been modified by Artic Maritime air, and it was this that gave the large scale impact of the storm event. Comparatively, the 5th December storm event was likened to the events of January 2012 and December 2011, however the length of the storm event, meant that the storm event in December 2013 had the most notable effect. The depression was also unusual because of the huge size of its cold sector, in comparison to the very small warm sector. It is clearly seen on the synoptic chart that 3 very large cold fronts with a noticeably larger cold sector are passing over, with the warm fronts of the depression being smaller than half the size. This unusual balance played a major role in the abnormal and extreme weather experienced.
Impact
In the case of this storm event it was clear that the physical impacts are what determined the location and extent of other type of impacts such as social and political impacts. A key physical impact that had a large influence on other impacts was that of high gusts of wind. As shown on the map on the right, winds in Scotland gusted at 60-80 knots and also exceeded 60 knots on the coasts of the Irish and North Seas. However it is clear that wind speed was itself influenced by other factors. Finally of the physical impacts was the storm surge experienced on the North Sea coastline with a 2m surge over predictions contributing further to flooding. So, as suggested, it was these physical impacts that sparked the majority of publicised impacts during the storm event. Overall the north of the UK was more heavily affected although the south was also effectively impacted. In Northern Scotland 100,000 homes were left without power, flights were cancelled at Glasgow, Edinburgh and Aberdeen airports. There were also two fatalities with a man aged over 50 having his lorry overturned and another man over the age of 70 was struck by a falling tree as far south as Nottinghamshire. The storm surge also caused heavy flooding and coastal erosion with 400 people fleeing flooded homes in Rhyl.