It's the news the organisers were dreading: the royal wedding could be a washout after forecasters warned of heavy showers on Prince William and Kate Middleton's big day.
Despite earlier predictions that the sun would shine on the newlyweds, cooler weather sweeping across Britain has brought the threat of a drenching for the thousands of people lining the streets on Friday.
If it does rain, the public will be denied the chance to see the bride and groom in an open carriage on their way back from Westminster Abbey. A closed-in carriage is on standby to be used in wet weather.
Helen Rossington, a senior forecaster at MeteoGroup, said: "At the moment, it is looking like temperatures will probably be a little bit above average (on the day) and there is a risk of heavy showers."
Tom Morgan, a spokesman for the Met Office, said that the day of the royal wedding would feel much cooler in England and Wales than of late due to a "brisk, north-easterly wind".
As well as a risk of showers in London, rain is a possibility in Ms Middleton's home village of Berks, where hundreds of people are expected to take to the village green for a tea party.
Most of the rest of the country, including western England, western Wales, the north of England, Scotland and Northern Ireland is forecast to enjoy a bright day with sun and warm temperatures on Friday.
St James's Palace remained upbeat despite the gloomy forecasts. "The rain will only add to the Britishness of the occasion," said a spokesman. "I'm sure it won't put people off coming to line the route."
In the case of rain, the prince and Ms Middleton will leave Westminster Abbey in the glass coach in which Diana, Princess of Wales, arrived at St Paul's Cathedral on her wedding day, rather than the open 1902 State Landau.
Other carriages being used to transport bridesmaids, page boys and senior members of the royal family are "convertibles" with hoods.
Dozens of umbrellas will be available for VIP guests.
The forecast comes after much of the country basked in a heatwave this bank holiday, with predictions that this month will beat the 2007 record for the warmest April. (© Daily Telegraph, London)