Climate of The United Kingdom - Sunshine and Cloud

Sunshine and Cloud

The average total annual sunshine in the United Kingdom is 1339.7 hours, which is just under 30% of the maximum possible. The south coast of England often has the clearest skies because cumulus cloud formation generally takes place over land, and prevailing winds from the south-west keep this cloud from forming overhead. The counties of Dorset, Hampshire, Sussex and Kent have annual average totals of around 1,750 hours of sunshine per year. Northern, western and mountainous areas are generally the cloudiest areas of the UK, with some mountainous areas receiving fewer than 1,000 hours of sunshine a year.

Valley areas such as the South Wales Valleys, due to their north-south orientation, receive less sunshine than lowland areas because the mountains on either side of the valley obscure the sun in the early morning and late evening. This is noticeable in winter where there are only a few hours of sunshine. The mountains of Wales, northern England and Scotland can be especially cloudy with extensive mist and fog. Near the coast, sea fog may develop in the spring and early summer. Radiation fog may develop over inland areas of Great Britain and can persist for hours or even days in the winter and can pose a major hazard for drivers and aircraft.

On occasions blocking anticyclones (high pressure systems) may move over the United Kingdom, which can persist for weeks or even months. The subsided, dry air often results in clear skies and few clouds, bringing frosty nights in winter and hot days in the summer, when some coastal areas can achieve almost maximum possible sunshine for periods of weeks.

Average hours of sunshine in winter range from 38–108 hours in some mountainous areas and western Scotland, up to 217 hours in the south and east of England; while average hours of sunshine in summer range from 294–420 hours in northern Scotland and Northern Ireland, to 592–726 hours in southern English coastal counties. The most sunshine recorded in one month was 383.9 hours at Eastbourne (East Sussex) in July 1911.