A flypast to mark King Charles's Coronation could be cancelled due to a high chance of showers, according to the RAF.
Air Chief Marshal Sir Michael Wigston said there was a '50/50' chance of the flyover going ahead over The Mall and Buckingham Palace tomorrow due to a 70 per cent chance of heavy rain.
It comes as 'heavy' and 'thundery' downpours are expected in some parts of England over the rest of the Bank Holiday weekend.
Sir Michael said: 'The weather isn't looking brilliant, but there's nothing we can do about it.
'We have to be safe, we have to make sure that we aren't taking any unnecessary risks.'
He added: 'We'll make a weather call one or two hours before the actual moment, but if there's rain and low cloud then it will be almost impossible to get it through.
'It's 50/50 at the moment, but we have lots of options, the decision will be made, at this stage we're hoping for the best.'
The King and Queen Consort's procession will set off from Buckingham Palace at around 10.20am, when there is likely to be light wind and rain.
Temperatures will then reach highs of 17C by the afternoon, which is around average for the time of year and 5C warmer than Queen Elizabeth II's 1953 Coronation.
After the service at Westminster Abbey ends, Charles and Camilla are expected to enter Buckingham Palace through the centre arch at 1.33pm.
Met Office meteorologist Alex Deakin said: 'There will be outbreaks of rain in London from 8am onwards, nothing too heavy, it's just going to be a bit grey, damp and drizzly.
'It won't rain all morning, just a bit on-and-off with some drizzle, it may stop for half an hour or so and come back again, that kind of thing.
'It will probably stay like that into the afternoon before it perhaps gets a little brighter but generally staying drab for most of the day.'