The climate of Snowdonia

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Sunshine and temperatures
In general, Wales has warmer temperatures throughout the year than Scotland, and has milder winter minimums than England, but cooler winter maximums than Northern Ireland. Over Wales the mean annual temperature at low altitudes varies from about 9.5 °C to 10.5 °C, with the higher values occurring around or near to the coasts. The mean annual temperature decreases by approximately 0.5 °C for each 100 m increase in height so that, on this basis, Snowdon (at 1,085 m) would have an annual mean temperature of about 5 °C. July is normally the warmest month in Wales, and the highest temperatures of all have occurred furthest away from the cooling influence of the Atlantic.

Sunshine totals throughout the year are more than that of Scotland, but less than neighbouring England. May is the sunniest month, averaging 186.8 hours.

Rainfall
Wales is wetter throughout the year than Northern Ireland and England, but has less rainy days than Northern Ireland; meaning that rainfall is more intense. Wales is also drier than Scotland in every month apart from May, June and December, and there are less days with rain than in Scotland. Throughout Wales, the months from October to January are significantly wetter than those between February and September, unlike places in south-east Scotland or in the English Midlands where July and August are often the wettest months of the year.

Winds
As with many mountainous regions, the landscape can have a very significant effect on the nature of wind speeds, with winds tending to be aligned along well-defined valleys. It is this gustiness which causes much of the damage to buildings and trees during storms.

Snowfall
Snow is quite frequent over the mountains and hills of Snowdonia. The average number of days each year when sleet or snow falls in Wales varies from about 10 or less in some south-western coastal areas to over 40 here in Snowdonia.
The average number of days with snow lying in Wales varies from six or less around the coasts to over 30 in Snowdonia.

Visibility
As many parts of Wales are some distance from the populous areas of Britain and mainland Europe, much of Wales enjoys excellent visibility. Given the mountainous nature of the country and its proximity to the sea, hill fog can be frequent and is a potential hazard to be borne in mind by walkers in Snowdonia.