Snow rarely lies on the ground at sea level before November or after April. On low ground in the Western Isles and in most coastal areas of Scotland, snow lies on average for less than 10 days a year, although this increases to around 15 to 25 days for coasts in the north and north-east. However, over the mountains snow typically lies for more than 50 days a year. Serious difficulties with roads blocked by snow are, fortunately, not common on low ground, but some higher roads in Scotland are regularly affected each year. In heavy snow there can be quite extensive drifting of the snow, especially over the higher ground.
Snow is deposited on leeward slopes with exposed areas often left relatively bare.
On the highest summits, such as Ben Nevis, snow cover typically persists for around six or seven months of the year. Facts and Figures Snow Graph Visibility Scotland often enjoys excellent visibility, since the greater part of the country is remote from the industrial and populous areas of Britain and mainland Europe. Even in the industrial areas of central Scotland the move away from coal fires for domestic heating and the decline in traditional heavy industry has reduced the incidence of smoke haze caused by local air pollution. Frequently, however, cloud with a very low base can shroud high ground with hill fog. The resulting low visibility, especially if further reduced by drizzle, can pose a hazard for hill walkers and motorists.