Heavy snow storms, which have stranded drivers for hours on motorways in the north of England, will make way for rain - sparking fears of flooding.
The M6 was blocked in both directions between junctions 25 and 27 in Lancashire when a sudden burst of more than a foot of snow brought drivers to a standstill around 8.30pm, said the Highways Agency.
Many became stuck along the stretch of motorway between Wigan and Standish after struggling to make it up inclines in the treacherous conditions, while a number of accidents including jack-knifed lorries also blocked lanes.
The M6, as well as the M56 and M58 which were also blocked, are now all moving again but remain heavily congested with long tailbacks, said Lancashire Police.
Chief Inspector Mike Adamson said: "We realised at about 11pm last night that this was going to be a major incident. Some of the drivers and passengers have been stuck for hours - it has been a very difficult night for them. We have set up a command centre at Charnock Services, where officers have collected hot drinks and taken them to those who are stuck."
Some of the stranded drivers passed the time with snowball fights and building snowmen, while others abandoned their cars completely. One man had to be taken to hospital by Lancashire Police after becoming ill in his car while it was stuck.
Mountain rescue workers walked along a four-mile stretch of the motorway overnight to check on the condition of drivers.
A diabetic man was taken to Royal Blackburn Hospital, while an ambulance taking a female patient to Royal Preston Hospital had to be dug out of the snow by Bowland Pennine Mountain Rescue team.
Phil O'Brien, team leader of Bowland Pennine Mountain Rescue, said: "It was potentially a very serious situation. The Highways Agency managed to get people moving at about 4.30 to 5am.
"There were hundreds of cars stuck but most people seemed in good spirits."