Weather forecasters have backed the decision of the royal couple to travel to Buckingham Palace in an open-top carriage.
Any showers are unlikely to hit central London until early afternoon, meaning Prince William and Kate Middleton should be able to make their way from Westminster Abbey to Buckingham Palace without getting wet.
The couple, who have opted to travel in the 1902 State Landau, are due to leave the ceremony at 12.15pm and arrive at the palace at 12.30pm.
Forecaster John Hutchinson of MeteoGroup, the weather division of the Press Association, said that the greatest risk of rain would not be until later in the day.
He said: "Some heavy showers will develop during the day across south-east England but the chance of any of these hitting the royal wedding is 35%, with the highest risk being the early afternoon. Thus this means we forecast a 65% chance of it staying dry."
Although the highest risk of showers is around the time of the royal couple's much-anticipated balcony appearance at 1.25pm, he said it was "more likely to be dry than wet".
There should even be some sunshine in the capital from around 9am as guests arrive at Westminster Abbey.
After a chilly 10C start at 7am in London, temperatures are expected to reach 18C by 1pm, and 19C or possibly 20C in parts of the capital later in the day.
The risk of rain in Kate Middleton's home village of Bucklebury, Berkshire, is higher than that in the capital.
In Royal Deeside, Aberdeenshire, temperatures were as low as -4.4C overnight but should warm up to around 15C. Those watching the wedding on big screens outside Balmoral Castle coffee shop should be treated to a dry day with sunny spells. One of the hottest UK spots promises to be in north-west Scotland where temperatures in places such as Oban could hit 20C.