Exactly how much snow had to fall on 25 December to make it a ‘white Christmas’?
While wintry weather can cause chaos in December, many of us still hope for snowfall when the big day rolls around. But how do forecasters define what constitutes a white Christmas?
What is a ‘white Christmas’?
According to the Met Office, an ‘official’ white Christmas only requires one snowflake “to be observed falling in the 24 hours of 25 December somewhere in the UK.” Traditionally, snowfall had to be observed from the Met Office building in London for it to count.
“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,” explained the Met Office.
“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 common are white Christmases?
Since a snowflake has fallen somewhere in the UK on Christmas Day 38 times in the last 54 years, we can expect that more than half of all Christmas Days will technically be a 'white Christmas'.
However, there has only been a widespread covering of snow on the ground (where more than 40 per cent of stations in the UK reported snow at 9am) four times in the last 51 years.
The last widespread white Christmas in the UK was in 2010. A highly unusual 83 per cent of stations reported snow on the ground (the highest amount ever recorded), and snow or sleet also fell at 19 per cent of stations on 25 December.
Why don’t we get as many white Christmases as we used to?
Between the 1550s and 1850s, white Christmases were more common, due to the period of cooling known as the Little Ice Age.
While conditions have warmed up since then, the change from the Julian to the Gregorian calendar in 1752 effectively moved Christmas earlier in the year, reducing the chances of a white Christmas. For this reason, we are more likely to see snow between January and March than in December.
The average probability of a white Christmas by location, according to the Met Office
London - 6%
Birmingham - 15%
Aberporth - 9%
Glasgow - 35%
Aberdeen - 53%
Belfast - 22%
Lerwick - 75%
Bradford - 14% (since 1971)
St Mawgan - 10% (since 1957)