March is set to go out with a balmy bang ahead of April's arrival with trademark showers.
Temperatures are expected to soar in parts of the South East to double the average on Thursday, with highs of 22C (72F) forecast in the London area, 20C (68F) in Norwich and 18C (64F) in Bristol and Nottingham.
Met Office forecaster Alex Burkill said: "We are dragging up really warm air from Iberia and with relatively calm conditions in the South East that's what is allowing temperatures to climb quite high."
However a split across the country running from south-west Wales to Yorkshire means those north of the line will have a cooler, cloudier day with a risk of rain.
Belfast, Glasgow, Aberdeen and Edinburgh will peak at 14C (57F), while the mercury will top out at 13C (55F) in Newcastle.
The warm air mass will edge south and eastwards on Friday, but temperatures are expected to remain well above average for southern parts before a wet start to the weekend.
"Saturday is looking quite showery across the whole of the UK, although Sunday will be a pretty decent day for most with calm and bright conditions," Mr Burkill said.
In the sunshine, highs of 16C (61F) and 17C (63F) could be seen in the south on Sunday - good news for the crowds expected to turn out for the Cancer Research UK Oxford and Cambridge Boat Races on the Thames.
Further north highs between 11C (52F) and 14C (57F) are more likely.