With over 53,100 people having signed up to be on the startline for the 26.2 mile race, it will be the cheering crowds who will have to be prepared against the cold and sunburn.
There are likely to be bright skies overhead, a breeze throughout the day, an outside chance of a shower but it is unlikely to snow for the first time in the event’s 35-year history, according to the Met Office. Forecaster Chris Page said: ‘Out of the sunny spells in the afternoon it will feel cold. The sun at this time of year is getting a bit stronger so there is a risk of sunburn even if it is a bit chilly.
‘The runners will be OK once they get going. It will be the spectators who will have to wrap up warm. ‘
‘In the sunshine it will feel pleasant if you are sheltered from the wind.’
Mr Page said there was a ’30 to 40%’ chance of a shower in the morning but, asked about the possibility of snow, he added: ‘It is highly unlikely the showers will have a wintry flavour to them.’
By the time the runners reach the startline in the morning, temperatures will climb from 3-4C (37-39F) overnight to 8-9C (46-48F). The maximum temperature is set to be around 12C (54F).
Any stragglers who are making their way to the finish line in the late afternoon will find themselves jogging home in slightly cooler conditions.
It is unlikely to be the coldest race day which was recorded at 7.6C (46F) at noon in 1994 or hottest which was the 21.7C (71F) reached in 2007.
Reports earlier this week had suggested that an unseasonal cold weather front was due to sweep in to London al from Friday onwards, threatening to usher in icy Arctic showers in place of the recent spells of sunshine.
Punters have been offered odds of 3-1 that there will be snow in London and of 100-1 that the event will be cancelled due to the weather.
Coral’s John Hill said: ‘The return of the wintry weather has promoted punters to back snowfall this weekend, something which is very rare for April,’ said Coral’s John Hill.
‘The London Marathon is one of the highlights in the capital this weekend and some punters have been backing the race to be interrupted due to the weather.’