A freak reversal of meteorological patterns next week will sweep a 17C plume of warmth in from the Continent.
After a wet and windy weekend, Britons will be back in T-shirts as mild air and sunshine bring a late blast of Indian Summer.
It will be driven by high pressure over central Europe shifting westwards towards the UK–opposite to the typical west-to-east movement of synoptic pressure features.
The unusual shift in weather patterns will kick the cold and wet weather into touch and make way for a late burst of warmth.
Jim Dale, meteorologist for British Weather Services, said: “This is an unusual phenomenon and can be looked at like the weather going backwards, or moving in the wrong direction.
“High pressure over central Europe will move westwards over France and Spain, and towards the UK.
“This will bring a flow of southerly air, and then around the middle of next week, a south-westerly airflow.
“It will turn unusually mild for the time of year.”
Temperatures in parts of the country could hit the mid- to high-teens through–around 10C higher than average for the time of year.
However, Britons gearing up for the mild spell will be facing another few days of wind and rain.
Mr Dale, author of Weather Or Not? said: “We have a few hoops to go through first before the mild weather arrives, I think on Wednesday and Thursday.
“But then with high pressure close by it will be more settled and much milder.”
Government forecasters promise that after the weekend Britons can look forward to a ‘steady climb’ in temperatures.
Retrogression is linked to a change in jet stream flow and the knock-on effects of the remnants of Atlantic Hurricane Martin.
Temperatures will stay around average through the start of the week before the mercury starts to climb, according to the Met Office.
Meteorologist Aidan McGivern said: “There will be a steady climb in temperatures into the start of next week and beyond.
“Through the next 10 days the temperatures trend looks like rising, and this to do with something we call retrogression.
“On Wednesday, low pressure close to the UK and a flattish jet stream will bring westerlies, hence the temperatures being closer to average.
“But then ex-Hurricane Martin is further away from the UK and the jet stream is diving a bit further south and is less flat and we have south-westerly winds, so we are changing from westerlies to southwesterlies hence the milder weather returning.
“That is called retrogression.”
Some forecasters warn, however, that after the mild spell, a blast of cold will be waiting in the winds.
The same high-pressure system responsible for next week’s warmth will move further west to pull cold air down from the north.
In the meantime, Britons are battening down the hatches for a wet and windy Guy Fawkes weekend.
Persistent rain dampened bonfires yesterday with more showers on the way into the start of next week.
The Met Office has issued a warning for rain across southern Britain where up to two inches could fall by the end of today.
A spokesman said: “Following recent heavy rain, which has left the ground saturated, a further spell of heavy rain is likely during Sunday morning, clearing eastwards through the afternoon.
“Some 20 to 30 mm of rain is likely fairly widely, with some places perhaps seeing 40 to 50 mm.”
Torrential downpours threaten travel disruption and flooding of homes and businesses, the Met Office warned.
The good news is, after the soggy start to the week, Britain’s weather will improve ahead of next weekend.
Netweather forecaster Ian Simpson said: “The UK’s weather has been stuck in a rut recently, with persistent low pressure to the west and north-west of Britain bringing very mild and changeable weather, with south-westerly and southerly winds.
“This pattern looks set to persist for most of the coming week, but there are growing signs that the pattern will shift as we head towards next weekend.”