Christmas is fast approaching, and one question that's on many people's mind is - will it be a white one?
The definition of a White Christmas in the UK is one single snowflake falling in the 24 hours that make up Christmas Day, at any observation site across the country. Since 1960 this has actually happened 38 times, suggesting that on average a White Christmas is more likely to happen somewhere in the UK than not.
However, as you would probably expect there is a large variation across the country as to how likely you are to see a white Christmas - in fact, your chances in southern England are fairly slim with just a 6% chance in an average year in London, the probability typically increasing the further north you go with, on average, 3 in every 4 years producing a white Christmas in the Shetland Isles.
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The 'snowiest' Christmas in the past 55 years, in other words the highest number of stations reporting sleet or snow falling (61%), was in 2004. However, many of us think of a white Christmas as one having a blanket of snow on the big day itself, and this is much rarer; the 'whitest' Christmas since 1960 was only 5 years back in 2010 where 83% of the weather stations across the country reported snow lying on the ground.
In actual fact, we are more likely to experience a White Easter than a White Christmas because in the early winter the seas around the UK are still relatively warm, and so any cold air approaching from the north or the east gets heavily modified by these warm seas, making it less likely to snow, especially to low levels in southern Britain. However, skip forward to early spring when Easter takes place, and the seas have lost a lot of their stored warmth through the winter season and are much colder - and so when cold airmasses arrive they are less likely to be modified, and more likely to produce snow.
Will it be a White Christmas this year? Keep checking the forecast as we get nearer to the big day...
Dan Holley 17th December 2015