The Met Office has issued a 14-hour weather warning for parts of the south west.
The yellow alert is in place from 10am tomorrow (Thursday) until midnight.
Thunderstorms and torrential downpours are predicted, with flooding in some areas likely - and even strong winds and hail.
The warning covers Somerset, Dorset, Gloucestershire, Wiltshire and beyond - although at present neither Devon nor Cornwall are included.
Thunderstorms and torrential downpours are predicted, with flooding in some areas likely.
A spokesperson for the Met Office said: "Thunderstorms are likely to break out in some areas, particularly during the afternoon and early evening.
"While most places will probably miss them, where thunderstorms do occur there is a chance that in a few places up to 40mm of rain could fall in an hour or so and 40 to 60mm could fall in two or three hours.
"These torrential downpours may be accompanied by frequent lightning, whilst gusty winds and hail may also affect a few places.
"The exact location of the thunderstorms will be hard to pinpoint, so the warning area will be kept under review and updated if necessary."
The maximum temperature is likely to be 26 degrees C, but it's the rain that could cause chaos as Glastonbury Festival begins.
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