West Scotland is one of the more exposed areas of the UK, being close to the Atlantic. The strongest winds are associated with the passage of deep depressions close to or across the UK. The frequency and strength of depressions is greatest in the winter half of the year and this is when mean speeds and gusts are strongest. The graph for Tiree shows a typical variation of the monthly mean speed and highest gust. November to March have the highest mean speeds with June to August the lightest winds.
The variation in monthly mean speeds (average of a continuous record) and highest gusts ('instantaneous' speed averaged over about 3 seconds) at Tiree is shown below.
Another measure of wind exposure is the number of days when gale force is reached. If the wind reaches a mean speed of 34 knots or more over any ten consecutive minutes, then that day is classed as having a gale. Over most inland, sheltered areas of the region the average is around 5 days per year but the coasts, islands and well exposed upland areas have more, with over 25 days with gale in the Hebrides in an average year. Wind speed is sensitive to local topographic effects and land use. Exposed places on coasts and hills will experience stronger wind speeds and more days of gale.
There have been several noteworthy gales affecting Western Scotland, accompanied by property damage and disruption to travel and power supplies. Examples include an intense depression on 15 January 1968 that produced an hourly mean speed of 53 knots and a gust of 89 knots at Glasgow airport and resulted in 20 fatalities and 2000 people being made homeless in Glasgow. The 'Boxing Day Storm' of December 1998 that tracked north-eastwards across Scotland produced a gust of 80 knots at Prestwick.
The direction of the wind is defined as the direction from which the wind is blowing. As Atlantic depressions pass by the UK the wind typically starts to blow from the south or south west, but later comes from the west or north-west as the depression moves away. The range of directions between south and north-west accounts for the majority of occasions and the strongest winds nearly always blow from this range of directions. Spring time also tends to have a maximum of winds from the north east, due to the build up of high pressure over Scandinavia at this time of year.
The wind rose for Prestwick illustrates the typical frequency of speeds and directions during the year through the Central Lowlands, with the enhanced SW direction that occurs there. In contrast the wind rose for Tiree is typical of sites on the islands, with topographic features generally absent and frequent strong winds.
