Dawkins McClusky

Nothing is so evocative of Christmas as the picture-postcard snow carpeted idyllic country scenes so often depicted at this time of year. Although snowfall typically occurs January-February in the UK, we still have high expectations for seeing the white stuff on the 25th December.
Much of the idea of a white Christmas originates from the paintings and literature from a period where global temperatures were much cooler than present averages, known as the ‘Little Ice Age’ (mid-1400s to 1900s). Charles Dickens’ classic ‘The Christmas Carol’ did much to reinforce this idea being set in a wintry snow-covered London, further helping to influence the common sense that snow and Christmas Day go hand-in-hand.
But what actually does count as an official white Christmas? According to the Met Office, any single snow flake falling at any time during the 24 hour period of Christmas Day anywhere in the British Isles constitutes a white Christmas. There are various other definitions, such as at least one flake of snow having to land on the roof of The London Weather Centre any time during Christmas Day. This isn’t the one we are using though.
As might be expected, there is a great deal of regional variation in the occurrence of a white Christmas under this official Met Office criteria, with some regions experiencing a higher number than others [Fig 1].
frequency of white christmas
Figure 1 Percentage occurrence of white Christmases for the period 1950-2009 in different regions of the UK (Met Office data). Northern Scotland experienced the highest number with 36 out of the 50 being white Christmases. At the other end of the country, the southeast and central southern England experienced the lowest number with 10 out of the total 50 being white Christmases.
It goes without saying that part of Scotland will always be snow-covered at this time of year due to the height above mean sea level. Eastern parts of England are more prone than other also, due to the air masses that sweep in from Scandinavia over the North Sea. The West Country (south west England) is quite vunrable to the prospect of snowfall, as cold northerly gusts can be pushed along the Irish Sea, and it’s precipitation contents deposited on the first land mass it meets.
With the last white Christmas in 2009, how likely is it that we will be seeing snowfall this coming December 25th? Certainly, this years lead-up has been very similar to conditions last year, with heavy snowfall from mid-November in parts of Britain. Arctic air masses are creeping in bringing in precipitation which, with cold enough weather could bring snow. This colder, denser air mass however is in a ‘duel’ with a warmer, less dense air mass. We are starting to see the introduction of Polar fronts which could influence our current weather greatly. As with last years ‘big freeze’, there is a depression off the south coast forecast by the Met Office, which could spell another cold snap. There will be an area of high pressure persisting to the west of the British Isles which will block any incoming low pressure systems from the Atlantic, and so will allow for cold air masses to come in from the north and the east.
Netweather.tv say that the average temperature so far for this December is -1.6°C below average, and that January 2011 will be -0.8°C below average for this month. These conditions fair well for likely snowfall accross the British Isles, and the lowest average temperature for England is around 3°C, so these temperatures would be perfect for increased snowfall.
So in the long term then, as a result of our ever heating planet, we will experience milder, wetter winters with marginally cooler and wetter summers also. Historically, the number of white Christmases has declined in recent years due to global warming, but judging by the characteristics from last years Christmas period, we could be in for some heavier snowfall in January and maybe February.
Another aspect of Christmas that excites people is the working out the chances of a white Christmas which has become somewhat of a sport, in which bookmakers go with the weather forecast to put out the odds against the public who like an informed bet at what the better will do over the Christmas period. The newspapers as a majority don’t think it will be a white Christmas, such as the Daily Times who are uncertain, and internet sites such as netweather.tv, who say that there is just a 30% chance of any parts of England seeing snow on the 25th December.
12% of all Christmases on record have been white in England, with Wales at a similar amount. Scotland have a bit more, with 20% but Northern Ireland have 22% white Christmas rate.
The odds are against a white Christmas this year, but snow will be more likely later on in the winter season.