UK Snow Climate
Snow climatology is discussed briefly in Chapter 1 of the PhD thesis, however further information is given here. Snow is relatively rare near sea level in England and Wales, for instance in coastal areas of Dorset, Devon and Pembrokeshire, however SW England and S Wales have seen the most notable blizzards that have occurred over the UK in recent history (for example 18-19 January 1881 and the 8-9 January 1982). More information on these heavy snowfalls can be found in Chapter 3 of the PhD. Despite being the mildest region of the British Isles, these heavy snowfalls over SW England are the result of a warm front approaching from a the south-west being separated from cold easterly winds from Eastern Europe, as the depression tracks eastwards across central Europe. Snow, generally is much more frequent over the hills of the Pennines and the Lake District, as altitude and distance from the sea plays an important role of which areas see snow falling and which districts allow snow to lie on the ground for any considerable time.
The number of days when sleet or snow falls in England and Wales varies from year to year, however in an average year it is about 5 days in coastal areas of Cornwall and Pembrokeshire to around 70 days in the Cumbrian area of the Pennines. Snow rarely falls before November or after May in England and Wales. With respect to snow lying on the ground, this also varies quite considerable from year to year, however in an average year the number of days snow lying on the ground in England and Wales varies from about 5 or less around the coasts of Cornwall, to over 90 in the Cumbrian area of the Pennines. A day of snow lying on the ground is defined as one with snow covering at least half of the ground at 0900 GMT.
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As air temperature generally decreases with altitude, precipitation that reaches the ground as rain at low-level sites, for example Anglesey, may fall as snow nearby over higher ground i.e. Snowdonia. Consequently, there is a marked increase with altitude in the number of days with snow falling and also the number of days with snow lying on the ground.
The average number of days with sleet or snow falling in Scotland ranges from around 20 or less across coastal areas of Ayrshire and Dumfries and Galloway to over 100 days across the Cairngorm range in the county of Grampain.
Snow rarely lies on the ground at sea level before November or after April in Scotland. 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 across Caithness and Grampian.
Across the mountains of the Highlands and Grampian, snow lies on the ground for more than 100 days a year. Some high-level, north-facing sides of mountains found in the Grampian area, particular snow beds are semi-permanent, only disappearing in very occasional summers. On the highest summits, such as Ben Nevis, snow cover typically persists for around 7 months of the year.
As mentioned above, the number of days of snow falling and lying on the ground varies enormously from year to year. In many districts of the UK, in the last 50 years it has ranged from none at all in a number of winters to in excess of 30 days during the winters of 1946/1947 and 1962/1963.
Even areas near the coast experienced prolonged snow cover during these two winters. In heavy snowfalls, there can be quite extensive drifting of the snow in strong winds, especially over the higher ground, resulting in severe dislocation of transport. Fortunately such occasions are comparatively rare.
Particular regions of the UK are more prone to see snow falling or lying on the ground with particular air masses. In SE and E England, snowfall is usually associated with an easterly airflow bringing in showers or by a warm front lying to the south of the region. These snow showers can often produce significant snowfalls across Kent, which is exposed to unstable instability north-easterly winds blowing onshore from relatively warm waters of the North Sea, for example the 11-14 January 1987. In NE England, N Scotland and E Scotland the exposure to northerly winds is also an important factor. Heavy snow or showers often falls across these regions, for example the 18-20 February 1941 that brought heavy snow to NE England, due to low pressure being located in the North Sea that brought in cold unstable Arctic and/or Continental air. The Midlands, NW England and Northern Ireland often see the snowiest conditions of the winter due to Arctic or Polar maritime airstreams (Polar Lows). These airstreams bring in frequent snow showers, due to the result of convective activity and instability over the Irish Sea. The Midlands can also see significant snow due to a shallow convergence under anticyclonic conditions in an easterly airflow.
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