The occurrence of snow is linked closely with temperature, with falls rarely occurring if the temperature is higher than 4 °C. For snow to lie for any length of time, the temperature normally has to be lower than this. Over most of the area, snowfall is normally confined to the months from November to April, but upland areas may have brief falls in October and May. Snow rarely lies outside the period from December to March.
On average, the number of days with snow falling is about 12-15 per year over the lower lying areas but about 20 days over the higher ground of the Chilterns, North Downs and Weald. The least snow-prone places are those close to the English Channel, with less than 10 days.
The number of days with snow lying has a similar distribution, with 5 days per year in most inland areas but over 10 days on the higher ground particularly to the east and north. These averages can be compared with parts of the Scottish Highlands where on average there are 60 days with snow lying and the coasts of SW England with less than 3 days per year.
The monthly averages of days with sleet/snow falling and lying at Heathrow and Lyneham are shown below (a day of lying snow is counted if the ground is more than 50% covered at 0900).
Kent and the Thames estuary are especially prone to falls associated with unstable east or north-east winds bringing snow showers in from the North Sea. Examples include 12 January 1987 when persistent heavy showers resulted in over 35 cm of level snow either side of the Thames estuary and 52 cm at East Malling, Kent with travel disruption, and early March 2005 when drifts of up 30 cm occurred over the Downs in Kent and East Sussex.
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