Heavy rain is set to batter parts of Britain with up to 20 to 30mm falling the space of three to four hours on Wednesday, forecasters warned as they issued yellow "danger to life" warnings for later this week.
Serious flooding has already closed roads in Northern Ireland where the River Bann burst its banks near the north coast leaving some roads underwater.
A yellow severe weather warning for rain was issued in counties Antrim and Down where winds gusted at up to 60mph in exposed areas.
Yellow weather warnings have also been issued for large parts of the south west and southern Wales on Wednesday and the south of England and the Midlands on Thursday.
These mean there is a small chance of fast flowing or deep floodwater, causing a danger to life and the potential for flooding.
Back in London Prime Minister Boris Johnson was to chair emergency Cobra meeting to discuss response to recent flooding in Sheffield and other parts of South Yorkshire where fire crews from Tyneside, Wales and Shropshire have been drafted in to help with the relief effort.
“Thursday will see rainfall from Kent to Newcastle and this reflects a weather front which is going to bring wintry weather in hilly areas, especially the Cotswolds and Brecon Beacons in Wales," Grahame Madge from the Met Office told The Independent. "This weather could also see rain turn into snow, including in the Midlands. But due to the ground being fairly warm from the summer it is unlikely that it will set.
Forecasters have also warned that temperatures could reach -4C overnight as the cold snap across the UK continues and a widespread frost continues to cover much of the country.
The mercury has been several degrees below average this week and the frigid temperatures will continue as a cold front from the north-west moves in, with snow likely in some higher regions
“It is going to be colder tonight than usual with widespread frost," said Mr Madge. “This is because of clear skies and we are expecting it to be widespread. It will be foggy in places and overnight the temperature could drop down to -4C in parts of Scotland.
“London will see temperatures of 4C, which will be the medium temperature, but places such as Buckinghamshire and Hertfordshire will be colder. However this can still cause problems, particularly if you are driving through it.”
Heavy snow is possible over the high ground in Scotland, England and Wales from Wednesday night. Up to 4cm is possible in the North East of England and 1cm could fall in the Peak District.