The Midlands area is one of the more sheltered parts of the UK, the windiest areas being in western and northern Britain, closer to the Atlantic. 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 December to February, and this is when mean speeds and gusts (short duration peak values) are strongest. The graph shows a typical variation of the monthly mean speeds and highest gusts.
The variation in monthly mean speeds (average of a continuous record) and highest gusts ('instantaneous' speed averaged over about 3 seconds) at Watnall 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 the Midlands generally, the average is around 2 days per year but exposed areas, especially in the west and north, usually experience about 5 gales per year. Wind speed is sensitive to local topographic effects and land use. Places sheltered by hills, or in extensively wooded or urban areas will have lower wind speeds and fewer days of gale.
There have been several noteworthy gales affecting the Midlands, accompanied by property damage and disruption to travel and power supplies. Examples include 2 January 1976 when a depression moving eastwards across Scotland to the North Sea brought storm force winds with gusts of 70-80 knots, the 'Burns Day storm' of 25 January 1990 when gusts of 60-70 knots were recorded widely and 27 October 2002 which again saw gusts of around 60 knots.
The direction of the wind 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 this range of directions. 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. In the Midlands, periods of very light or calm winds with no preferred direction usually occur for around 5% of the year.
The annual wind rose for Birmingham airport (Elmdon) is typical of open, level locations across the region, with a prevailing south-westerly wind direction through the year.
A tornado is a violently-rotating column of air, caused by the rapid displacement of warm moist air by cold dense air often associated with the occurrence of active cold fronts. It will typically last for a few minutes, track across the land for 2 to 5 km and have a diameter of 20 to 100 metres. On average, 33 tornados are reported each year in the UK although the number can vary significantly from year to year. The UK has the highest frequency of reported tornadoes per unit area in the world, although they are nowhere near as intense as those reported in the USA.
One of the strongest tornadoes to affect the UK in 30 years struck Birmingham on the afternoon of 28 July 2005. Over 420 homes were damaged with about 122 sustaining serious roof damage when a tornado with estimated 110 knot winds ripped through the Kings Heath, Moseley, Sparkbrook and Balsall Heath areas of the city. Fortunately there were no fatalities, but 3 people were seriously injured, and about 1000 trees were uprooted some of which blocked roads.
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