April 2012 - Wet and windy
April 2012 was the wettest April in the UK as a whole since records began in 1910. Within the UK there were some marked regional variations across the UK. Much of the rainfall was focused on the south.
A record breaking month
April 2012 was the wettest April on record in the UK since records began in 1910. By April 29 Liscombe in Somerset had seen 273.8mm of rain, more than 3 times the 86.4mm average. April contrasted sharply to March which was the fifth driest March on record for the UK. There was also a marked regional variation across the UK. In Scotland Prestwick (Ayrshire) had only 39.2mm of rain and Skye had only 52mm of its 99.5mm average.
In another reversal of the norm, April was also cooler than March, the first time this has happened since 1998.
Quite often when we think of the weather in April we think of sunshine and showers (hence the term 'April showers') but the month brought some prolonged spells of wet and windy weather with deep areas of low pressure and active frontal bands affecting the UK.
The weather chart (below left) is for 0600 on 28 April 2012 and the weather radar (below right) is for the same time. Air flows in an anticlockwise direction around the low pressure which is situated over NW France. Winds across the UK are from the northeast. The lines around the low are isobars which are lines of equal pressure. The closer the isobars are then the stronger the winds are. Can you see that the position of the frontal systems correspond with the position of the rain on the weather radar?
The weather chart (below left) is for 0000 on 29 April 2012 and the weather radar (below right) is for the same time. The low pressure is situated between SW England and NW France and the strongest winds are across SW England, this time from the SE.
Widespread flooding so why the continued drought?
Many parts of England had been suffering from a well publicised drought. Why did the rain during the 28 and 29 April 2012 lead to so much flooding across the UK? If an area has been suffering from drought conditions then to ease the drought conditions sustained rainfall is needed to replenish the ground water levels. If a lot of rain falls in a short period of time then it does not have time to replenish the ground water levels and the rain flows straight to streams and rivers which are prone to bursting their banks.
Despite the amount of rain received in April many areas remained in drought. These areas were East Anglia, the Southeast, South and East Yorkshire, the Southwest and the Midlands. River flows responded and were normal or higher for the time of year and reservoir levels had increased somewhat.
It takes more time and rainfall to undo the effects of two dry winters on groundwater stores.
Strong and gusty winds
Many parts of southern England were affected by gusts of 50-60mph and numerous trees were blown down. As discussed earlier it had been a recording breaking month for many parts of the UK in terms of rainfall and the windy conditions of the last weekend caused further disruption with many areas affected by flooding as well as gale-force winds.