Snow is one of the most variable aspects of the British climate - variable both in space and in time. Snow or sleet is observed to fall on just two days per year on average in the Isles of Scilly, 12 days in central London, 16 in Manchester, 20 in Edinburgh, 35 in Aberdeen, more than 50 at Aviemore and Braemar, and 170 days on the summit of Ben Nevis. Snow covers the ground in the Isles of Scilly on an average of one day every eight years, on three days per year in central London, nine in Manchester, 15 in Edinburgh and Aberdeen, 65 at Braemar and over 200 days on Ben Nevis.
If we consider low-lying districts only, there is a trend from southwest to northeast, with the coasts of Cornwall, south Devon and Pembrokeshire often snow free, while snow is also comparatively rare on other west-facing coasts such as those of Lancashire, Galloway, Ayrshire and Argyll. People who live along the North Sea coastline are much more likely to wake up to a snow-cover, with the highest probability in northeast Scotland. However, the main influence on the frequency of snow-cover is altitude. Very roughly, there is an increase of one day per winter for every 15 metres above sea-level. Thus Plymouth has an average of one day with snow on the ground while Princetown on Dartmoor has 28 such days; Central London has three, but Hampstead Heath has 13 and Leith Hill in Surrey 25; Manchester has nine but the eastern outskirts of Oldham and Rochdale have 25 and Saddleworth Moor has 40.
There is also a huge contrast in the frequency of snow-cover from year to year. Except on southern and western coasts, completely snowless winters are uncommon. In the London suburbs, for example, there was no snow on the ground in only five of the last 50 winters. In Birmingham there has been just one snow-free winter in the last half century, but the majority of years have fewer than ten days with a snow-cover; by contrast the severe winter of 1962-63 had 75 such days while those of 1978-79 and 1946-47 had 60 each.
The number of days with snow on the ground is the conventional way of describing how snowy a winter has been. Unfortunately, it gives no indication of the abundance of snow, only its persistence. In the UK we keep records of the depth of snow each day, but not of the aggregate snowfall for a season. The deepest level snow in a populated area during the 20th century was 1.65 metres - near Ruthin in northeast Wales in March 1947, and at Tredegar in southeast Wales in February 1963.
