Showers looks set to affect both Reading & Leeds Festival and the Notting Hill Carnival over the weekend.
The Met Office said there was also potential for thunder and lightning at Reading and Leeds on Saturday, as thousands of people flock to the major English festivals.
Jonathan Vautrey, meteorologist at the Met Office, said: “There’s a reasonable chance that some showers will pass over Leeds and Reading over the course of the day.
“Particularly for Leeds, they are within the yellow warning area that we currently have out just because winds are going to be lightest across that north-eastern area of England today.
“That will mean those showers are slower moving at times, so rainfall is likely to accumulate in specific locations a bit more.”
Mr Vautrey said some localised flooding and minor disruption in Leeds could be possible.
He added that both Leeds and Reading “do have the potential for seeing some lightning and thunder” over the course of Saturday, but rainfall would be the main issue.
There will be a reduced chance of lightning in Leeds on Sunday, but sharp, heavy downpours remain likely and could merge into longer spells of rain.
Reading will see “a good number of sunny spells” on Sunday morning, but showers will move over from the West before easing off in the evening.
The Notting Hill Carnival will be a similar situation to Reading on Sunday with showers from around lunchtime, the forecaster said.
For the rest of Saturday, Mr Vautrey said: “It’s stayed relatively dry so far [in Notting Hill], but we are now just starting to see those showers begin to bubble up.
“There’s still going to be sunny spells in between these showers, so it’s not going to be a complete washout all day in London both today and tomorrow.”
