Heavy rain is expected to disrupt more than two million return journeys at the end of the Easter weekend.
The Met Office said drier spells will turn cloudy with patchy rain for much of England and Wales on Sunday, before up to 15mm of more persistent and possibly thundery rain on Monday.
The RAC and transport analysis company Inrix said 2.01 million leisure journeys will be made by car on Easter Monday.
The lengthiest delays are expected to be between 10am and 12pm, and drivers have been advised to wait until later in the day and travel in the evening.
An area of cloud in the North Sea will spill over into southeast England and push west towards Wales on Easter Sunday, the forecaster said.
This will lead to grey conditions and patchy rain across southern England, while the South West could see heavy showers.
Kathryn Chalk, meteorologist at the Met Office, said: “We’ll see further spells of heavy rain coming in, pushing its way northwards through Easter Monday.
“Probably a damp start, especially across Wales, central England and northeastern parts as well with further heavy spells of rain here.
“Further towards the south, if we do see any clouds breaking up we could see heavy showers again in the afternoon.”
The heaviest of the rain on Monday will likely be in a corridor from southwest England up to East Anglia, Ms Chalk said.
No weather warnings have been issued, but the showers could see between 5mm and 15mm of rainfall.
Scotland and Northern Ireland will hold on to much brighter spells with odd, scattered showers across both of the days.
The outlook will remain unsettled after the long weekend, with low pressure dominating and spells of heavy rain likely.
