Once again kids will be peering out of their bedroom windows this Christmas, hoping it will snow, while their parents will be consulting the weather report, hoping it won’t. While a bit of winter weather certainly adds a touch of magic to Christmas, it can also cause winter travel chaos.
Weather forecasters do their best to predict when snowfall will occur in a particular region, but predicting the winter weather is one of the toughest jobs they have.
Will it snow?
When you think about it, there are so many questions that people want answered about snow, over and above what can be displayed on a simple weather map. To predict a heavy fall of snow, the type that will lead to snowman and tobogganing, the forecasters need to know when it will start to snow, how long it will snow for, how heavy the snow will be, what the ground temperature will be and, of course, will it snow at all, or will it rain or sleet instead.
Then, to add to the weather forecaster’s problems, people aren’t interested in a large-scale weather map that predicts that there will be snow their region, they want a weather report for their own town.
What you need for snowfall is just the right mixture of temperature and moisture. For snow to form, there needs to moisture in the atmosphere and the temperature needs to be at, or below, freezing. You can’t forecast a white Christmas, though, by checking the ground temperature on Christmas Eve, it’s the atmospheric temperature that matters, so you will still need to rely on the weather forecasts.
Will the snow accumulate on the ground?
What the ground temperature will tell you is whether or not any snow that does fall will accumulate on the ground. Despite what many people believe, it can never be too cold to snow. However, even if the weather map shows that snowfall is likely in your area, if the ground temperature rises above 5 degrees Celsius (41 degrees Fahrenheit) is very unlikely that the snow will settle on the ground although it’s not impossible.
Snowflakes can also vary considerably in size and type. Snowflakes are formed when individual snow crystals clump together. Most snowflakes are less than half an inch across, but, if you have very cold ground temperatures, snowflakes can get as big as 2 inches across. Some people have even reported seeing snowflakes as big as dinner plates.
What type of snow will it be?
To further confuse matters, there are actually different types of snow. While many snowflakes do take on the familiar star shape, there are more than 30 different types of snowflake. Seeing a weather map with wintery weather forecast doesn’t guarantee that the snow will be white either. Snow is actually translucent; it’s not white at all. Snow absorbs very little light, which is why it appears to be white, but in some circumstances you can get snow that appears to be blue or pink.
So will it be a white Christmas the year?
Whether you are hoping for a white Christmas in the UK, or somewhere else in Europe, whilst the weather maps and weather forecasts will give you a good idea of what the weather might be like on Christmas Day, there is no guarantee, one way or the other. That’s great news for the kid’s and not such good news for anyone who has to travel.