Parts of southern England and Wales will be hit by severe thunderstorms today, the Met Office has warned.
Forecasters have said that flash flooding and lightening could cause problems throughout this afternoon.
The Met Office said: "A band of thunderstorms will move quickly eastwards, perhaps leading to some localised disruption."
A yellow warning is in place between noon and 6pm, with forecasters saying transport services could be affected.
It comes after a spell of unusually mild weather which yesterday saw the UK record the warmest New Year's Day on record.
But this will not last, experts have warned.
Warm subtropical air from the Azores has seen Brits enjoy unseasonably mild weather but change is on the way thanks to an Arctic chill due to blow in from next week.
The Met Office said that 16.3C had been reached in St James's Park, central London, meaning it is "likely to be confirmed" as a record maximum temperature for any New Year's Day.
Met Office forecaster Dan Stroud urged people to "make the most of the warm weather, because a change is on the way as we go into the early part of next week".
It's forecast to be colder everywhere by Tuesday with d aytime temperatures expected to plunge to as low as 3C in Edinburgh and 7C in London and Cardiff.
He said: "We are going to be losing the sub-tropical air flow and replacing it with some things from the north.
"Temperatures will definitely go back to average, with a return of frost and some snow in the forecast across north areas and across the hills."
It comes after the Met Office said temperatures increased overnight to reach 16.5C in Bala, Gwynedd, north Wales, during the warmest New Year's Eve on record.
Met Office forecaster Craig Snell said January will see a drop in temperatures due to an Arctic chill forecast to hit next week.
Yellow weather warnings for wind and snow have been issued for Tuesday and Wednesday.
Up to five inches of snow and 70mph winds are possible in Angus, Grampian, Highlands & Eilean Siar and Orkney & Shetland.
