Runners lining up for this Sunday’s London Marathon can look forward to balmy conditions, with temperatures expected to climb to 21°C as the capital enjoys a springtime mini-heatwave, according to the Met Office.
The 2025 edition of the world-famous event is tipped to break records, with over 56,000 participants set to cross the finish line—making it the largest marathon ever staged globally. And it won’t just be the course bringing the heat, as the weather takes a warm turn following a turbulent April.
Race day will start off on a cooler and cloudier note, with light breezes accompanying the early runners. Temperatures at the start line in Greenwich Park are forecast to be around 10°C as the elite wheelchair athletes set off at 8:50am, followed by the elite women at 9:05am and the elite men at 9:35am. The mass start will then take place in waves from 9:35am until around 11:30am.
As the morning progresses, brighter skies are expected to push in from the west, lighting up the route that winds past some of London’s most iconic landmarks — Cutty Sark, Tower Bridge, Canary Wharf, the London Eye and finally the grand finish at The Mall, near Buckingham Palace.
By midday, the mercury is likely to rise to a pleasant 18°C, peaking around 21°C in the afternoon as the majority of runners are finishing. While the sunshine is welcome news for spectators lining the streets, marathon organisers have advised participants to stay hydrated and pace themselves carefully in the warmer-than-usual conditions.
The sunny weather marks a sharp contrast to the wet and stormy end to the Easter Bank Holiday period, which brought heavy downpours and even thunderstorms to parts of the UK. The past week has seen a mixture of mild spells and unsettled conditions, but now forecasters say London is on the brink of a sustained spell of warmth.
Dan Stroud of the Met Office commented: “After a fairly damp and unsettled few days, we’re seeing things turn warmer and drier just in time for the London Marathon. While some cloud cover will linger early on, it should break up and give way to sunshine for much of the race.”
He added: “The dry spell will be welcome news for marathon organisers, though we’re also seeing this as a chance for some early-summer warmth that will likely continue into next week.”
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Indeed, the warm weather isn’t stopping on Sunday. Temperatures in London are forecast to hit 22°C on Monday and climb even further to 24°C midweek — marking the hottest stretch of the year so far. A mini-heatwave is expected to take hold, with the south-east in particular seeing prolonged sunny periods under high pressure.
While many will welcome the sunshine, especially after a chilly and damp early spring, the recent dry weather has also raised concerns. The London Fire Brigade has reported a spike in fire-related incidents, with over 2,200 emergency calls made in early April — more than double last year’s figure for the same period. Outdoor fires in parks and wooded areas have also seen a sharp increase.
Still, the Met Office believes next week’s high-pressure system will bring mostly fine and settled conditions, with only brief interruptions likely to affect the north-west of the UK.
Whether running, cheering or simply soaking up the atmosphere, Londoners are in for a spectacular weekend. With record numbers on the course and picture-perfect weather on the cards, the 2025 London Marathon promises to be one to remember.
