Britain could face more snowfall and strong winds later this week if Storm Christoph moves in.
The Met Office warns that colder air may enter if lower pressure arrives later in the week.
Storm Christoph has set off weather warnings for heavy rain across the UK.
Met Office spokesman Oli Claydon said rain was the main concern “initially” – but that will change.
He said, “As we go through the week and the low pressures that these persistent and heavy rainfall fronts bring with them for the next few days … as that low pressure moves east and into the North Sea, the winds really become a thing later during the week.
“Even as the low pressure eases, it pulls a northwesterly stream of air down, which again brings much colder air through the UK, which then creates another snow risk.”
Mr Claydon said the situation is one of “schedules of various hazards throughout the week, but the first hazard is certainly rain and that is reflected in the warnings at the moment”.
The most serious weather warning – amber against rain – has been in place in parts of the Midlands and northern England since Tuesday morning.
There are also less severe yellow warnings of rain in Wales, Northern Ireland, Northern England and Southern Scotland.
The highest rainfall recorded overnight was at Aberllefenni in West Wales, where it fell 35.4mm between midnight and 8 a.m. on Tuesday.
Of the areas in the Amber Warning Zone, Bolton in the Greater Manchester area has seen the most rain so far at 24.4 mm in the same period.
By Wednesday, the yellow rain warnings will extend south to cover the whole of England, all of which will stay in place until Thursday noon, along with the more serious amber warning in Central England.
Eastern Scotland faces a yellow warning of snow from Wednesday afternoon through Thursday noon.
This will cause travel delays, power outages and rural communities to become isolated.
Mr. Claydon said, “It will not be a brief outbreak of bad weather as you might think of past storms where it burns through quickly overnight.”
“It’s really persistent heavy rain, the rain is going to be really persistent and only continue until today and tomorrow and Thursday. It’s really just the persistent accumulation of rainfall and not a brief weather event,” he said.
On Tuesday, the Environment Agency issued 15 flood warnings and 117 less serious flood warnings across England.
Floods have already risen in parts of the country.
A motorist was shown stranded in Leicester while workers in York prepared flood protection near the River Ouse on Tuesday morning.
A serious incident has already been reported in South Yorkshire, which could indicate flooding in the coming days.
Doncaster Mayor Ros Jones tweeted Monday night, saying, “Major risk areas have been inspected in the past 36 hours, sandbags have been distributed in flood risk areas and will continue for the next 24 hours.”
The Local Government Association (LGA) has advised people to check with the councils to keep up with the progress of the storm system.
The LGA said in a statement, “They will share flood warnings and other relevant information, so people should make sure they regularly check their council’s website and social media and follow their advice.”