Comments: Weather news - wet start to the year and weekend rain
Release Date 05 June 2014
University of Reading experts have today commented on the possible weekend floods, the cause of the forecast storms, and some stats about the British weather in 2014 so far.
Dr Roger Brugge, meteorologist, said:
"The start of 2014 has been the wettest first five months of any year on record. Following the wet winter, spring (March-May) has also seen more rain than normal this year. At the University of Reading's observatory 194 mm of rain fell - about 50 per cent more than normal - making it the wettest spring here for six years.
"So far this year the rainfall total at the University tallies 462 mm, some 25 mm more than in any other January-May period in the past century in Reading. The same five months have also been much milder than usual - although 2007 and 2011 were even warmer."
(Note: continuous weather records at Reading go back to 1908 - i.e. more than a century)
Dr Hannah Cloke, flooding expert, said:
"We could see flash floods in some parts of Britain if rainfall this weekend is as intense as has been predicted,. The problem is likely to be exacerbated in areas where the ground is still wet from the winter floods, particularly in catchments with high groundwater levels and where rivers are still high following Britain's wettest winter ever.
"Urban areas and small, steep catchments are likely to be vulnerable, especially those with little soil to absorb the water. Some towns and major roads could be quickly swamped as drainage systems become overwhelmed.
"But when it rains very heavily, almost anywhere could be at risk. Extremely intense bursts of rain can mean that the soil is simply unable to soak up the water fast enough, so excess water runs off and causes floods in all sorts of unexpected places."
Dr Rob Thompson, meteorologist, said:
What's going to happen? (based on the forecasts)
"A low pressure system sitting off the west coast of Ireland pulls warm, humid air north from France. The front from the system passes the UK adding extra possible uplift for storms. This is the perfect recipe for an explosive thunderstorm."
Forecasts
"On Wednesday afternoon the Met Office severe weather warning was yellow, meaning ‘Be Aware' across England, Wales and Southern Scotland. The yellow warnings were first generated yesterday. The forecasts for location are likely to become more specific as we near the weekend.
"It is likely that there will be intense thunderstorms with very heavy rain, providing the potential for flash flooding.
"A scientific team, funded by the Natural Environment Research Council and led by the University of Reading, is currently researching how we can improve forecasts of convective summer storms which can cause flash floods. These are currently difficult to predict, meaning people can sometimes have little or no warning they are in harm's way."
What causes thunderstorms in the UK?
"The kind of convective thunderstorms forecast for Saturday are caused by rapidly rising air.
"Hail is also often associated with thunderstorms. The size of hail is indicative of the strength of the updraughts. Hail in the UK is rarely very large as we do not have the conditions for the kind of intense updraghts seen in places like the US. The largest hail stone reported worldwide was about 20cm in diameter, and weighed a kilogramme.
"Other dangers of storms are from winds, including ‘microbursts', where air rapidly descends from the storm creating sudden wind changes in speed and direction. These can be very hazardous to aircraft.
"Tornados can also be a feature. While ‘Tornado Alley' in the USA sees some of the most destructive tornados, southern Britain actually gets more per square mile - but the British versions tend to be very weak compared to their American counterparts."
Myth busting
"Some media reports have suggested that a hail storm in 1843 caused a five-foot deep crater - this is not accurate, but contemporary reports suggest the storm did lead to drifts of hailstones which lay five feet deep on the ground. The storm did cause very large hail stones, about 7cm diameter, which wouldn't be unusual for a US supercell storm.
"Temperature forecasts this weekend are for low 20s C, although it will most likely be very humid and so feel hotter than it is."