Wales is one of the windier parts of the UK, with the windiest areas being over the highest ground and along the coasts, particularly those facing directions between north-west and south.
The strongest winds are associated with the passage of deep areas of low pressure close to or across the UK. The frequency and strength of these depressions is greatest in the winter half of the year, especially from November 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 Valley 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 10 consecutive minutes, then that day is classed as having a gale. At low altitudes in Wales, gales occur most frequently in the south-west of Pembrokeshire with about 30 days of gale on average. Other coastal areas average 15 days or more of gale each year with the number of days decreasing inland to 5 days or fewer. Wind speed is sensitive to local topographic effects and land use - places sheltered by hills or in urban areas will have lower wind speeds and fewer days of gale.
There have been several noteworthy gales affecting Wales, accompanied by property damage and disruption to travel and power supplies. Examples include the 'Burns Day storm' of 25 January 1990, when gusts of 60-70 knots were recorded widely and one of 93 knots occurred at Aberporth, and 27 October 2002 which again saw gusts of around 60 knots with 84 knots recorded at Mumbles, near Swansea. The highest gust recorded at a low-level site in Wales is 108 knots at Rhoose (Vale of Glamorgan) on 28 October 1989.
Wind direction is defined as the direction from which the wind is blowing. As Atlantic depressions pass 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 these directions.
The annual wind rose for Valley on Anglesey is typical of coastal locations in Wales, with a prevailing south-westerly wind direction through the year. However, there is a high frequency of north to north-east winds in spring.
