The number of hours of bright sunshine is controlled by the length of day and by cloudiness. In general, December is the dullest month and May or June the sunniest.
Sunshine duration decreases with increasing altitude, increasing latitude and distance from the coast. Local topography also exerts a strong influence and in the winter deep glens and north-facing slopes can be in shade for long periods.
In Northern Scotland the sunniest places are close to the Moray Firth and in the southern Outer Hebrides, where the annual average approaches 1300 hours. Many other coasts average about 1200 hours but sunshine averages are lower inland, and are lowest over the mountains and Shetland (less than 1100 hours). The sunniest places on mainland UK are along the south coast of England, with over 1750 hours each year on average, whilst the Channel Islands enjoy over 1900 hours.
The average monthly sunshine totals for Lerwick and Inverness are shown, together with the highest and lowest totals recorded in the stated periods. The sunniest month of the year is normally May, rather than June, because of the tendency for settled anticyclonic weather in late spring. The Western Isles in particular can experience sunny conditions in May and record high values have been achieved, such as the 300 hours at Prabost (Skye) in May 1975.
