Warm air from the Continent will sweep into the UK ahead of the weekend pushing thermometers to a possible 19C – around 10C higher than usual.
However, a change in wind direction towards the end of the month, or perhaps sooner, will replace mild southerlies with frosty northerlies.
Weather models reveal the risk of snow not just across the mountains of Scotland, but down to central England and Wales.
James Madden, forecaster for Exacta Weather, said: “We fully expect a significant pattern change to much colder conditions which threaten wintry blasts and snow from the middle of the month onwards.
“We could see the first significant snow of the season during this period through the end of November and into the start of December.
“This wintry weather will extend to some lower levels of the country.”
The U-turn will be driven by the same weather system responsible for the unseasonal warm spell.
High pressure creeping in from Eastern Europe will sweep mild southerly winds around its southern flank into Britain.
As it moves further east into the Atlantic, the UK will be in the path of Arctic winds pulled in around the northern edge of the system.
Temperatures will plummet to freezing across northern Britain while the rest of the country sinks into single figures.
Mr Madden said: “High pressure will be influential in this pattern change.
“This is going to drive temperatures into the high teens in parts of the south throughout the resto of this week with 18C or 19C possible in parts of the country.
“This is very mild for the time of the year but will pave the way for the arrival of much colder conditions later.”
Temperatures will rocket later this week as wind and rain makes way for clearer skies and drier weather.
High pressure from the east will stretch across the Atlantic pulling warm air up from the Continent and the tropical Azores Islands, off the coast of Portugal.
South-eastern parts of the country will get the best of the weather, while wind and rain will continue to hammer the northeast, according to the Met Office.
Meteorologist Aidan McGivern said: “Wednesday looks like a less showery day than Tuesday with a better chance of some sunshine coming through and longer dry periods towards the east in particular.
“A change comes along later Wednesday, more persistent bands of rain push into western Scotland, but there will be clearer spells towards the southeast.
“This southeast-northwest split becomes a feature of our weather during Thursday and Friday.”
The change in weather will unleash strong winds across northern Britain as further heavy rain pummels the region, he warned.
But winds from the south will bring “exceptionally mild” temperatures for the time of year, he added.
He said: “The winds are coming in from the south and southwest and as a result, weather fronts will push into the northwest with very strong winds at times and persistent rain.
“But higher pressure on the Continent will exert its influence on the southeast and it will tend to be drier here, and with this fetch from the southwest it will be exceptionally mild for the time of year, especially across northern parts of the UK.”
Forecasters agree, however, that the cold will not be far behind with something very different in store for late November.
Jim Dale, meteorologist for British Weather Services, said: “After this mild spell, then we have got the cold plunge.”