London Marathon competitors could be running in snow this weekend for the first time in the event's 35-year history.
An unseasonal cold weather front is due to sweep in to the capital from Friday onwards, threatening to usher in icy Arctic showers in place of the recent spells of sunshine.
This weekend's weather is a real contrast from the warm temperatures and long spells of sunshine enjoyed across Britain earlier this week. On Wednesday, temperatures reached 18C in north Wales, making it the hottest day of the year so far.
Met Office forecaster Sara Thornton warned that while occasional showers can be expected throughout Friday, "really the emphasis is on some cold winds coming in from the North over the weekend".
"The rain knocking on the door is coming in on Friday, it's moving northwards, probably getting as far north as parts of Wales and the Midlands, before it tracks back towards the South in the early hours of Saturday," she said.
"Temperatures are down quite a bit in some places, not even in double figures, but that's nothing compared to what we will see as we go throughout the weekend.
"A cold plunge of Arctic air is moving in throughout Saturday, spreading colder air to all parts as we head through the weekend."
While temperatures may hover around the 10C mark for much of the weekend, forecasters have warned that icy gusts will make it feel notably colder. In many parts of the UK, temperatures may dip to between 4C and 6C as the cold weather moves southwards.
However, the Met Office pointed out that temperatures would not drop low enough for any snow to settle, meaning the impact on running conditions would be minimal.
Moving north, large parts of the Midlands and Wales can expect sleet and showers, with snow likely to fall in parts of Scotland. Scattered showers are also expected in the North and East of England.