Snow forecasting in the UK
Forecasting snow will always be a challenge in the UK. This is because of the UK's geographical position between the Atlantic Ocean and continental Europe and the variable weather patterns we experience.
The type of weather we get in the UK depends on where the air has come from. The coldest directions in the winter are generally when the wind comes from the Arctic Circle to the north or from the continent to the east. When the UK sees these conditions, it brings a higher chance of colder weather - and the possibility of snow.
Will it snow?
There is often a fine line between whether it will rain or snow in a particular location. Some of the factors influencing whether it will snow or rain are:
- The UK is on an island surrounded by sea. During the winter the sea temperatures are warmer than land temperatures which can often lead to rain around the coasts but snow a few miles inland.
- The higher you are the more likely it is to snow due to temperature dropping with height. Rain showers may fall as snow in mountainous areas.
- The UK can be affected by a variety of air masses. If we get contrasting air masses over the UK in the winter we can often end up with a 'battle ground' situation. This often occurs when cold dry continental air from the north or east bumps into relatively mild moist maritime air from the south or west. Where these air masses meet snow is possible, but a lot depends on which air mass wins the battle.
When battle ground situations occur, in one location it can be snowing but just 20 miles down the road it can be sleeting or even raining. This is because there is a fine line between the boundary of the warm and cold air.
- In marginal snowfall situations, urban areas can be less likely to get snow due to the warming effects of the surroundings. There have been situations where central London has seen rain and sleet, but just outside the M25 there has been heavy snow.
- If rain falls continuously through air with a temperature as high as 6 °C, it may cause the air temperature to fall low enough for the rain to turn to snow. This is due to heat being absorbed by the evaporation of water vapour from the raindrops as they fall, leading to the reduction in temperature.
Did you know?
Thirty centimetres of fresh fallen snow has about the same water equivalent as 25 mm of rainfall.
Last updated: 26 March 2015