THREE-quarters of an inch of rain could fall in heavy showers later today, warns the Met Office.

It issued a yellow 'be aware' warning from midday until 11pm, saying many places will be dry this afternoon, but scattered heavy showers and thunderstorms will develop and continue through the evening in places with possible localised surface water flooding.

The chief forecaster said: "Showers will clear away to the northwest this morning, with the cloud continuing to break to allow some sunshine. This in turn will allow the temperature to rise sufficiently to trigger shower development through the afternoon, with some becoming heavy, thundery and slow moving, for example over parts of southwest England.

"Hail is also possible in some of the showers.

"The heaviest showers and thunderstorms could produce 20mm (0.79inch) of rain within an hour."

Areas covered by the warning are Wiltshire, Swindon, Bath and North East Somerset, Bristol, Cornwall, Devon, Gloucestershire, North Somerset, Somerset, South Gloucestershire and Dorset. 

Meanwhile forecasters say there will continue to be a chance of scattered showers all bank holiday weekend, mainly on Saturday across south Wales and the south west.

By Monday a new spell of wet weather moving slowly westwards from the east.

Matthew Dobson, of Meteogroup, said: "If you want to avoid the rain for the longest on Monday, then heading west looks a good call, based on the latest forecast data."

Meanwhile severe thunderstorms are set to sweep parts of France, Italy and the Alps this weekend which could prove dangerous for those enjoying outside activities.

Dobson said: "Over the next few days, temperatures across the near continent are set to rise strongly as winds from a southerly direction develop over Spain, France and Germany.

"On Friday and Saturday, temperatures in Paris will reach 24C, Berlin can expect to see 27C by Sunday and inland parts of central and northern Italy should see the mercury topping out in the low 30s Celsius on Friday and Saturday.

"The UK is more likely to be 'side-swiped' by these balmy southerly flows, with our winds blowing from an easterly direction instead.

"While this is bad news in winter (when easterly winds bring bone chilling cold air from Scandinavia and Russia), at this time of year an easterly can sometimes bring rather warm conditions to central and western parts of the UK, while eastern coastal counties are cooler, due to the effect of the North Sea. London will see 19 or 20C over the next few days, the warmest we have seen since the first week in May.

"As warm air builds over central and southern France, the Alps, northern Italy and Germany, we have to be concerned with an area of low pressure that is currently spinning away above the Bay of Biscay.

"Stronger winds and cold air at higher altitudes will overspread the warmth and humidity already in place over the aforementioned areas. This will provide a trigger for the development of widespread heavy downpours and thunderstorms.

"Conditions seemed primed for the development of severe thunderstorms, capable of producing very frequent lightning, large hail (perhaps golf ball sized or larger), intense rainfall capable of flash flooding, strong and damaging winds and perhaps even a tornado.

"These nasty storms are most likely across south-eastern France, the Alps and northern Italy. This is where warmth and moist air look to combine best with increasingly strong winds through the depth of the atmosphere.

"At this time of year, walking, hiking, road cycling and mountain biking excursions to the Alps and surrounding regions are very popular.

"This weekend's conditions could be quite disruptive or even dangerous for these activities, especially if people are caught out and not aware of the forecast. Temperatures over the Alps will fall very sharply between Saturday and Sunday as the hot air is rapidly shunted away to the east."