The western and northern parts of Northern Scotland are, on average, the windiest in the UK, being fully exposed to the Atlantic and closest to the passage of areas of low pressure. The frequency and depth of these depressions is greatest in the winter half of the year, especially from December to February, and this is when mean speeds and gusts (short duration peak values) are strongest.
The variation in monthly mean speeds (average of a continuous record) and highest gusts ('instantaneous' speed averaged over about 3 seconds) at Lerwick is shown below.
Spring time tends to have a maximum frequency of winds from the north east. This seasonal effect is due to a build of high pressure over Scandinavia at this time of year.
The annual wind rose for Lerwick is typical of open, level locations across the Northern and Western Isles, with a prevailing south-west wind direction through the year and frequent strong winds. In the Highlands, winds are much lighter and generally directed along valleys. For example, at Aviemore south-westerly winds are very dominant, influenced by the Spey valley.
