More than 200 flood alerts are in place across the UK as heavy rain mixed with melting snow marks the latest weather battle.
There have been more reports of flooding in south Wales overnight as the downpours replace almost two weeks of snow, said weather experts.
Norfolk Police have reported flooding caused by melting snow and ice, which has closed a number of roads in the area.
Wales, central England, and the south west will be the worst-hit areas where at least one inch of rain is expected to have fallen by mid-morning, while the rest of the UK can expect around half-an-inch.
Rising temperatures of up to 12C have sparked a rapid thaw of the snow and ice which has built up in the recent cold snap, further exasperating potential flooding problems.
The Environment Agency has issued 30 flood warnings, urging people to take immediate action against predicted flooding, in the Midlands, the west of England, central England and Wales. A further 218 flood warnings are in place across England, Scotland and Wales affecting all but the east of England and north of Scotland.
Chris Burton, a forecaster for MeteoGroup, the weather division of the Press Association, said: "The rain started falling overnight in the west and will move east across all areas of the UK, with at least half-an-inch falling in most areas.
"The worst affected areas will be Wales and the south west. We have had some reports of flooding in south Wales which have had heavy downpours. There is also likely to have been some in north England and the Midlands where there is a large amount of snow melting.
"But from mid-morning the rain should lift and it should remain largely dry, with some scattered showers. Winds of up to 60mph will also cross the UK today."
He added that the heavy rain will return on Monday along with the risk of flooding as the surface water and river levels build up ahead of an unsettled week.