Britain is to be plunged back into winter as icy winds blow in from the North Pole.
Hail, sleet, snow and thunder will sweep the country for a week, with temperatures in the north below zero, experts said.
The RAC said: “Dig out the de-icer and scraper.”
Southern areas also face the risk of flash floods, just days after Britain basked in sunshine nudging 25C.
Heavy downpours are expected to lash the London Marathon.
A blast of bitter cold air from the Arctic threatens to send temperatures below zero across the country from Sunday.
Icy winds from the North Pole will make it feel close to -10C in the north next week with snow and harsh frosts expected.
Although slightly warmer in the south it will still feel much cooler with daytime temperatures struggling to get above low double figures.
The dramatic plunge means Britain will go from being hotter than Turkey and Ibiza to colder than Moscow, Stockholm and Finland in the space of a week.
The Met Office has forecast rain throughout Sunday morning in the capital with the chance of thunderstorms and heavy downpours early on.
Spokeswoman Laura Young said: "It is going to be much cooler widely next week due to a Polar maritime air mass moving across the country.
"Anywhere in the UK could see wintry showers although in the south it is more likely over higher ground.
"The marathon is looking cooler and wet, so it is a pretty miserable outlook especially for onlookers standing around in the rain."
The dramatic change is due to the jet stream taking a sudden southwards plunge allowing cold air from the north to flood into the UK.
Piers Corbyn, forecaster for WeatherAction, said: "Next week is certainly going feel like a return winter and will be very different to the warm weather we have just had.
"A cold plunge is on the way again the result of this wildly deviating jet stream which has led to ups and downs in the weather through the first part of this year.
"It is set to nosedive southwards again opening the gates to cold air from the north, a very chilly end to April is likely."
The grim forecast comes after Britain basked in what looked to be one of the warmest Aprils on record.
The chilly outlook also floors earlier forecasts which suggested Britain could be in for a long, hot run up to summer.
The chilly forecast prompted motoring experts to warn drivers to take care on slippery roads and make sure cars are ready for "winter weather".
RAC spokesman Simon Williams said: "Much of the UK has enjoyed summer-like conditions in the last few weeks, but motorists are going to need to be on their guard from this weekend as the weather looks set to take an abrupt about-turn with conditions more akin to winter.
"Ice could once again catch drivers out - so dig out the de-icer and scraper from the garage, and check those washer fluid levels.
"And, if you live further north or in Scotland, be prepared for some April snow showers that could quickly make driving conditions treacherous."
