Bank holiday Monday is set to be a wash-out with rainy weather on its way, the Met Office said.
Saturday will be the best day to get out and about in the capital as forecasters predicted some sunnier periods, with the odd scattering of cloud.
Those attending the first day of Notting Hill Carnival on Sunday and SW4 Festival in Clapham will be able to avoid the rain, as weather experts predict mostly fine weather.
But Monday is set to be chilly and showery, which may cause disruption to the hundreds of dancers and floats travelling through west London.
The Met Office said the cold temperatures are set to continue throughout next week, with some parts of the UK colder than Siberia.
Helen Rossington, a forecaster with MeteoGroup, said: "This weather pattern is likely to continue, and winds are not going to be from the south west again until the last couple of days of August, which may bring some warmer temperatures, though with the risk of rain."
