It is officially the warmest day of the year so far after temperatures reached 17.5C in Weybourne, Norfolk, today.
The unseasonably warm weather - more akin to the May Bank Holiday - is the result of air being blown up from north Africa and Spain, forecasters say.
The mercury could rise even further today with 18C possible in parts of the east of England, the BBC reports.
It comes after the Met Office issued two rain warnings for north-west Wales and Cumbria today.
BBC forecaster Chris Fawkes said: "The weather in the UK has gone from something like being stuck in a deep freezer to something unusually warm.
"With air coming up from north Africa and Spain across England and Wales that's where the temperatures are at their most unusual.
"It is already the warmest day of the year so far. Temperatures will probably reach 18C across parts of east of England which is very unusual for February."
Despite the warm weather, the Environment Agency has issued four flood warnings for England today, meaning flooding is expected.
The Met Office has also put out rain warnings for north-west Wales and Cumbria, where more than three inches of rain could fall in places.
The Cumbria alert says: "Heavy rain will continue during Tuesday night with moderate to heavy rain persisting for much of Wednesday before easing during the evening.
"A further 15-30 mm of rain is expected quite widely across the warning area with a further 60-80 mm over some high ground."
Meanwhile, the Met Office's Welsh warning says: "Rain across north Wales will.... persist until later on Wednesday, leading to 30-50 mm quite widely across the warning area, and locally 80-90 mm across Snowdonia."
