The Met Office has warned of up to three weeks of rainfall as part of a weather alert in force across Britain.
The warning predicts up to 90mm of UK rainfall in parts of Devon and Cornwall.
Another two rain warnings have been put out for sections of the south-east and south-west, raising the prospect of flooding.
The downpours are linked to a weather front created by Storm Elsa, which is currently in the Atlantic.
Met spokesman said, “It will bring a considerable amount of wind and rain to parts of the UK.”
Devon and Cornwall will take the brunt of the wet weather, with another inch of rain possible on weekends.
The Met Office has warned that some communities may be cut off by floods over the next 24 hours as rivers burst their banks.
The Environment Agency has issued 14 flood warnings and 167 less serious flood alerts in England.
The average monthly total rainfall for December in the UK is 120.2mm.
A rain warning has also been issued for an area of Scotland today, with flooding possible near Dundee.
The alert is due to start at 9pm today and will finish at 9am tomorrow.
Despite the wet conditions, temperatures are not expected to dip below 0C today.
Forecasters predict unseasonably warm weather for most of the country.
Parts of Yorkshire and Northumberland were also coated in white.
Some dry and bright weather across central and northern areas at times this morning.
However, rain will soon move north to across parts of southern Britain, before affecting central areas through the afternoon.
Met Office five-day weather forecast
Today:
Some dry and bright weather across central and northern areas at times this morning. However, rain will soon move north to across parts of southern Britain, before affecting central areas through the afternoon. Windy for many but rather mild.
Tonight:
Rain continuing north into Scotland and Northern Ireland. Further rain spreading north to affect southern and central areas overnight. Another mild night, with winds gradually easing.
Friday:
Rain at first across eastern England and northwest Scotland will gradually clear. Elsewhere, brighter with some sunshine but also a few sharp showers in the southwest.
Outlook for Saturday to Monday:
Sunshine and scattered showers, mainly in the west. A longer spell of rain is likely to affect the south on Saturday night. Temperatures near normal with overnight frost increasingly likely.
