The Met Office has issued an amber warning for Cumbria with up to 120mm (4.7in) of rain predicted in some areas.
Alerts have been put in place from north Wales to southern Scotland, with north west England worst affected.
Cumbria is still recovering after some areas were hit by flooding three times in less than a month.
See the latest news from Cumbria.
Hundreds of properties were affected when Storm Desmond brought a record amount of rainfall during the weekend of 5 and 6 December.
A few days later rivers burst their banks during a further deluge, with some communities flooded for a third time on Tuesday.
lan Goodman, from the Met Office in the north west, said the forecast for overnight into Boxing Day was becoming increasingly specific as time passed.
He said: "The emphasis if anything is shifting towards the south-eastern end of Cumbria.
"But, there's still potential for some quite significant rainfall that would result in renewed flooding."
Meanwhile, the Environment Agency said it had deployed additional high-powered pumps at the pumping station in Ulpha to deal with current or future flooding problems.
Sand bags have been handed out to properties at risk, and Environment Agency staff and forces personnel are on standby in case of emergency.
People can access information from council websites and the Environment Agency Floodline.
The agency is also operating a phone line - 0345 988 1188 - which will be staffed rather than offering recorded information.
Live flood warnings from the Environment Agency and the Scottish Environment Protection Agency.
View the flood map by tapping on the image below
Tap here for up to date flood information.
Flood-hit areas are braced for further problems with more heavy rain forecast for Christmas night and Boxing Day.