A month's worth of rain and 65mph winds are set to batter parts of the UK - while the south is gripped by a freezing fog.
The Met Office has warned that more than 100mm of rain could potentially fall in parts of Scotland over a 30-hour period.
The rain warning, which starts at 6am on Thursday and ends at noon on Friday, also says wind speeds may reach 65mph in north-west Scotland.
Met Office forecaster Helen Roberts said roads may be flooded in the wet weather .
She told Mirror Online: "North-west Scotland hasn't had a lot of rain this autumn so rivers should be able to cope with the rain fairly well, it will be more of a surface water issue.
"Elsewhere it will remain chilly in the south over the next few nights, with frost and freezing fog and sunshine by day. It will be cloudier in the north."
The Met Office weather warning for Scotland states: "Blustery showers will turn to more persistent rain on Thursday morning, turning heavy at times and continuing for the rest of the day.
"The rain will be accompanied by gale force southwesterly winds, with potential for gusts of 55-65 mph around coasts and hills.
"The rain will turn more showery overnight though further heavy and prolonged showers are likely on Friday morning. 40-60 mm of rainfall is expected widely across the warning area, but nearer 70-80 mm over the west Highlands and a few prone mountain locations could exceed 100 mm within a 30 hour period.
"The showers will become more scattered by Friday afternoon, by which time the winds will also have eased."
The average monthly rainfall for December in the UK is 120mm, according to the Met Office.
The Environment Agency has issued four flood warnings and 25 less serious flood alerts.
Tonight will be dry and mostly clear but there will be cloud around some western coasts.
It will remain clear for much of England and Wales through the night but Scotland and Northern Ireland will be mostly cloudy with patchy rain in the west.
Brisk south-westerly winds are expected in the north and west.
Tomorrow morning will be sunny in Wales, northern and western England with fog patches in southern and eastern England.
In Scotland and Northern Ireland there will be cloud and outbreaks of rain.
Rain will push into the far north-west of England and Wales in the afternoon.
The Met Office has revealed that this autumn was the wettest on record in South Yorkshire, Nottinghamshire, and Lincolnshire.
England as a whole has had its fifth wettest autumn with 348mm.
However, northern and western Scotland had a drier than average autumn.
Met Office five-day weather forecast
Today:
Most areas dry, with variable cloud. Patchy fog and frost in the south may take its time to lift, but should allow some spells of wintry sunshine in places. Northwest Scotland will be milder but with a little drizzle.
Tonight:
Cloud will come and go across the south, allowing patchy frost and fog again. Many other areas dry but drizzle in far northwest Britain is replaced by wetter, windy weather.
Wednesday:
Rain in the far northwest will cross many northern areas, easing and followed by clearer skies and blustery showers. Dry and rather cold further south; some sunshine after fog clears.
Outlook for Thursday to Saturday:
Patchy frost in the south Thursday, before rain, heavy across western Scotland, pushes southeast. Showers follow for Friday, before further spells of rain or showers Saturday. Milder generally, often windy.
