Along with the rest of South West England, Somerset has a temperate climate which is generally wetter and milder than the rest of the country. The annual mean temperature is approximately 10 °C (50.0 °F). Seasonal temperature variation is less extreme than most of the United Kingdom because of the adjacent sea temperatures. The summer months of July and August are the warmest with mean daily maxima of approximately 21 °C (69.8 °F). In winter mean minimum temperatures of 1 °C (33.8 °F) or 2 °C (35.6 °F) are common. In the summer the Azores high pressure affects the south-west of England, but convective cloud sometimes forms inland, reducing the number of hours of sunshine. Annual sunshine rates are slightly less than the regional average of 1,600 hours. In December 1998 there were 20 days without sun recorded at Yeovilton. Most the rainfall in the south-west is caused by Atlantic depressions or by convection. Most of the rainfall in autumn and winter is caused by the Atlantic depressions, which is when they are most active. In summer, a large proportion of the rainfall is caused by sun heating the ground leading to convection and to showers and thunderstorms. Average rainfall is around 700 mm (28 in). About 8–15 days of snowfall is typical. November to March have the highest mean wind speeds, and June to August the lightest winds. The predominant wind direction is from the south-west.