Met Office experts warn Friday night revellers could get a soaking after revising warnings for heavy storms hitting Northamptonshire.
Thousands are expected to hit county's town centres on the first weekend in 17 months nightclubs are able to open in pubs can serve 'vertical drinkers.'
But one 48-hour yellow warning in force from midnight tonight (July 23) has been replaced with two, the first of which starts at 8pm on Friday and carries through to 10pm on Saturday.
A second warning covers the period from 9am to midnight on Sunday.
Experts warn of wind, rain and storms which may lead to flooding and transport disruption in some places although Northamptonshire could escape the worst of the downpours until mid-morning Saturday.
A Met Office spokesman said: "Heavy rain and thunderstorms will move into southern areas during Friday night reaching south Wales and the Midlands early on Saturday.
"This is likely to bring frequent lightning, possible large hail and gusty winds as well as torrential rainfall for some.
"More heavy showers and thunderstorms are expected to develop across southern and eastern England on Sunday.
"Some of the heaviest showers are expected to affect the southeast of England late morning after a period of early morning rainfall before developing more widely across the warning area during the afternoon.
"Torrential downpours may develop in some places with hail and gusty winds additional hazards.
"Rainfall amounts will vary considerably from place to place, but there is the potential for up to 80-100 mm to build up in some locations over the course of the day."
The weather could also scupper star gazers' hopes of a good view of the bright Thunder Moon which is due to peak at 3.36am on Saturday.