The Met Office has issued a yellow weather warning for thunderstorms, threatening to rain off thousands of Platinum Jubilee celebrations events across the UK.
The yellow warning covers south west England from midnight Friday right through until Saturday morning and warns of heavy rain and localised flooding.
While many places will stay dry as the Queen's jubilee celebrations continue, the threat covers much of the south until Saturday morning.
Picnics and events have been planned across the country as part of the Big Jubilee Lunch, but sodden ground could see many having to be cancelled.
If the downpours are severe, there is a chance that homes and businesses could flood, with damage to some buildings from floodwater, lightning strikes, hail or strong winds.
More than 16,000 street parties are due to take place over the four-day bank holiday weekend, but weather elsewhere still looks to be mainly dry, meaning most can go ahead.
A spokesman for the Met Office told Yahoo News UK: "On Friday afternoon the best of the sunshine will be across northern Scotland, the far southwest of England and Wales and the southeast.
"It will also brighten up across much of southern Scotland and northern England, but elsewhere will be relatively cloudy with a risk of showers."
"From Saturday, there is still a good deal of uncertainty in the forecast," he said.
"Settled weather is on the cards for most northern areas with patchy cloud and sunny spells. However, a plume of warm air from the continent will influence the weather in southern and central areas, bringing showers here that could turn heavy and thundery at times."
On Sunday, more than 200,000 local events will take place across the country as part of the Big Jubilee Lunch, including screenings, street parties and picnics.
Themes being planned include red, white and blue and dancing through the decades with a world record attempt for the longest street party and the biggest Big Jubilee Lunch.
More than 600 Big Jubilee Lunches are also planned in more than 70 countries across the world, from Greenland to New Zealand.
Watch: Beacon lighters struggle against strong winds