Will it be a white Christmas?
For many of us, snow is synonymous with Christmas. Bing Crosby famously dreamt of it, while movies, advent calendars and Christmas cards are all decorated with snow-filled scenes of a white Christmas.
However, for most parts of the United Kingdom, Christmas is only at the beginning of the period when it's likely to snow. We are more likely to see snow between January and March than in December with snow or sleet falling an average 3.9 days in December, compared to 5.3 days in January, 5.6 days in February and 4.2 days in March.
White Christmases were more frequent in the 18th and 19th centuries, even more so before the change of calendar in 1752 which effectively brought Christmas day back by 12 days. Climate change has also brought higher average temperatures over land and sea and this generally reduced the chances of a white Christmas.
What is a white Christmas?
The definition that the Met Office uses to define a white Christmas is for one snowflake to be observed falling in the 24 hours of 25 December somewhere in the UK.
Traditionally we used to use a single location in the country to define a white Christmas which was the Met Office building in London. However, with the increase in betting on where will see a white Christmas, the number of locations have increased and can now include sites such as Buckingham Palace, Belfast (Aldergrove Airport), Aberdeen (Pittodrie - Aberdeen FC), Edinburgh (Castle), Coronation Street in Manchester and the Millennium Stadium in Cardiff.
We also analyse the data from our observing stations around the UK to provide a complete picture of where snow has fallen or was lying on Christmas Day.
How likely is a white Christmas?
We can accurately forecast if snow is likely on any given Christmas Day up to five days beforehand. In terms of the statistical likelihood of snow based on climatology, we know that a snowflake has fallen somewhere in the UK on Christmas Day 38 times in the last 54 years, so we can probably expect more than half of all Christmas Days to be a 'white Christmas'.
However the Dickensian scene of widespread snow lying on the ground on Christmas Day is much rarer. There has only been a widespread covering of snow on the ground (where more than 40% of stations in the UK reported snow on the ground at 9 am) four times in the last 51 years.
When was the last white Christmas?
The last widespread white Christmas in the UK was in 2010. It was extremely unusual, as not only was there snow on the ground at 83% of stations (the highest amount ever recorded) but snow or sleet also fell at 19% of stations.
We also had a white Christmas in 2009 when 13% of stations recorded snow or sleet falling, and 57% reported snow lying on the ground.
Technically, 2015 was also a white Christmas in the UK with 10% of weather stations recording snow falling, however none reported any snow lying on the ground.