Bing Crosby sang about it, children hope for it and the idyllic image dominates festive cards and movies the world over – a white Christmas.
For many of us, snow is synonymous with the Yuletide season, and we often dream of waking on December 25 to a thick blanket. But can we expect a white Christmas in 2012?
According to the Met Office, that’s a difficult question to answer. Only five days beforehand can it accurately forecast if snow is likely on Christmas Day, and the process itself is challenging because of the UK's geographical position between the Atlantic Ocean and continental Europe, and the variable weather patterns we experience.
There is often “a fine line between whether it will rain or snow in a particular location”, the Met Office says. Factors include sea temperatures, the height of the region and air masses – that is, when cold dry continental air from the north or east bumps into relatively mild moist maritime air from the south or west.
When this “battleground situation” occurs it can be snowing in one location but just 20 miles away sleeting or raining, the Met Office says.
And when it comes to white Christmases, the definition is important. While many of us would describe it as a complete covering of snow falling between midnight and midday on December 25, the classification used most widely - notably by those placing and taking bets - is for a single snowflake to be observed falling in the 24 hours of December 25 at a specified location, perhaps among a mixed shower of rain and snow.
The Met Office explains: “In terms of the statistical likelihood of snow based on climatology, we know that a snowflake has fallen on Christmas day 38 times in the last 52 years, therefore we can probably expect more than half of all Christmases to be a 'white Christmas' in this sense.
“Snow lying on the ground on Christmas Day - as we would expect from typical Christmas scene - is much rarer. 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 on the ground at 9am) four times in the last 51 years.”
The UK saw “quite a few” white Christmases between 1961 and 1970; from 1978 to 1981 and 1993 to 2001, “and a couple in recent times”, a Met Office spokesman told This is Somerset. “In between they have been fairly sparse.”
The spokesman explained: “There are many potential reasons for these periods of high and low frequency, as UK winter climate can be affected by things like the El Nino/La Nina cycle, solar UV output, and long-term cycles in the Atlantic ocean (North Atlantic Oscillation, Atlantic Multidecadal Oscillation).”
The last white Christmas was in 2010. It was extremely unusual, the Met Office says, as not only was there snow on the ground at 83 per cent of stations - the highest amount ever recorded - but snow or sleet also fell at 19 per cent of stations.
We also had a white Christmas in 2009, when 13 per cent of stations recorded snow or sleet falling and 57 per cent reported snow on the ground.
But how have white Christmases changed over the years? They were more frequent in the 18th and 19th centuries, the Met Office says.
Climate change has also played a part, bringing higher average temperatures over land and sea and so generally reducing the chances of a white Christmas. However, a Met Office spokesman explained “while globally we have seen 0.7C of warming since pre-industrial times, it’s not possible to say whether this would have had any impact on our regional climate for something as specific as white Christmases.
“The natural variability in the climate system is the dominant factor here”.
What’s more, there are suggestions the decline in the amount of Arctic sea ice may result in harsher winters within the UK and northern Europe.
But there may still be a chance to bring out the sledges and build snowmen even if a white Christmas isn’t on the cards, the Met Office says. This is because wintry weather is more likely between January and March than December – snow or sleet falls on average five days in December, compared to 7.6 days in January; 6.8 days in February and six days in March.
Visit This is Somerset for the latest snow updates.