An amber rain warning has been issued for parts of northern and central England as Storm Christoph approaches.
The Met Office told people in Yorkshire and the Humber, the North West, East Midlands and the east of England to expect heavy rain and potential floods.
Yellow warnings have been issued for England, Wales, Northern Ireland and southern Scotland.
Up to 70mm (2.75in) of rain is forecast to fall within 48 hours in the worst-hit areas from Tuesday.
The Met Office said the downpours, set to last throughout Tuesday and Wednesday, were likely to cause flooding when combined with melting snow on higher ground.
It said there was a "danger to life" due to fast-flowing or deep floodwater, and warned some communities there was a good chance they would be "cut off" by flooded roads.
'Protect your property'
It also predicted delays and cancellations to public transport, with the amber warning in place until 12:00 GMT on Thursday.
Councils and emergency services have warned people to prepare for potential flooding.
Mayor of Doncaster Ros Jones declared a major incident in South Yorkshire ahead of possible flooding.
In a tweet, she said emergency protocols were instigated on Sunday, with sandbags handed out in flood-risk areas, and told people not to panic but to be prepared.
Calderdale councillor Scott Patient urged residents and businesses to "take all the steps they can to protect themselves and their property".
Due to Covid-19 restrictions, Mr Patient said, the authority was preparing "virtual community support hubs" to help people if there was flooding.
"The virtual hubs work similarly to the physical ones, but everything will be done remotely to reduce the need for face-to-face contact and to protect staff, volunteers, those affected by flooding and vulnerable people in our communities," he said.
The Environment Agency has 14 flood warnings - meaning "immediate action" is required - in place across England, stretching from the south east to the north east.
Met Office forecaster Jon Griffiths said about 40-70mm (1.57-2.75 in) of rain was expected in the north-west over three days, potentially rising to 100-120mm (3.93-4.72 in) in hilly areas.
Mr Griffiths said river systems in some areas were already close to capacity.