Severe weather warnings are being issued as the snowstorm that deluged the US heads to Britain, bringing up to 8ins (20cm) of rain in some areas.
The rain from Storm Jonas is due to hit on Tuesday and Met Office warnings have been issued for most of Wales, the north-west of England, and south and west Scotland.
Yorkshire, which has already suffered catastrophic flooding this winter, has also been issued with a severe weather warning.
People in the Midlands and south-west of England have also been told by the Environment Agency to “prepare for the risk of flooding”.
Many parts of the warning area could see up to 4ins (10cm) of rain, while in the north-west, south-west Scotland and north Wales as much as 8ins (20cm) of rain could fall.
Chris Wilding, from the Environment Agency, said: “Our thoughts are with all those who have suffered serious flooding over the past few months, and it is once again vital that people prepare for heavy rainfall and the risk of further flooding.
“We will issue flood warnings and alerts where necessary as rivers respond to the rainfall, which could also inundate drains, so people need to be ready for flash flooding in some places.
“We urge people to check their flood risk, prepare for flooding, follow the advice from emergency services and never risk driving through flood water.”
Sky News weather presenter Isobel Lang said: “We are expecting some unusually high January temperatures of 15C or possibly 16C through Sunday and Monday.
“Although not record-breaking, this will be well above the average of 6 or 7C. The southerly airflow is in complete contrast to the northerly blast which has been pounding the north-east states of America where there has been significant disruption from a major winter storm.
“That depression will affect us in the UK this week, having crossed the Atlantic, it will bring us another surge of mild but very moist air resulting in heavy rainfall.
“The Met Office has issued a yellow warning for heavy rainfall for Tuesday and Wednesday for more than 6ins (15cms) of rain across western hills, bringing the threat of flooding.”
In the US, 11 states declared emergencies and at least 20 people died as the giant blizzard shut down large parts of eastern America.
The winter storm dumped up to 30ins (75cm) of snow on Washington DC on Saturday night.
Thousands of flights from major airports across the country were cancelled – 45 of which were heading for the UK.