London Marathon 2027 weather: what race day will likely feel like

The 2027 TCS London Marathon is the Double: for one year only, 100,000 runners over two days, Saturday 24 and Sunday 25 April, on the same 42.2 km route from Greenwich to The Mall, past the Cutty Sark, over Tower Bridge, round Canary Wharf and along the Embankment. Here's what race day has usually felt like, section by section, for a runner in the middle of the field.

What will the weather be like at the 2027 London Marathon?

Usually cool and breezy: good running weather for most of the field. In the records, a runner from the 09:30 Sunday start began at about 10° and finished at about 13°, with a dew point near 6°. RunFast's engine rated race day Good on 6 days in 10, Fair on 3 and Tough on 1.

The heat stress (WBGT, the number race medical teams use) was usually about 14°. It reached Moderate or more on about 1 day in 10, and High on less than 1. The warmest race day in the records reached 26°.

The records look at the two weeks around 25 April, so they speak for the Saturday too. Saturday runners start about half an hour earlier, at the organiser's likely 09:00.

Where does the weather usually cost runners time?

Mostly the wind, rarely the heat. On the middle day of the records, the weather cost a 6:20-per-km runner about 3 to 4 minutes over the whole race, and 9 minutes or more on 1 day in 10. The wind was the main cause on about 8 of those days in 10.

Start · BlackheathWoolwichCutty SarkTower BridgeCanary WharfFinish · The Mall1234567Historic

On a middle day no stretch is hard: the green stretches cost almost nothing, and the amber ones are a little slower, by about 1.5 to 2%. At the start to Woolwich, and at Tower Bridge and The Highway, amber is where the course turns into the north-easterly. Most of the last 16 km, from the Isle of Dogs to Westminster, is amber too, but there it's the warmth of the later morning, not the wind. Green is the run west through Charlton and Greenwich. The breeze is usually from the north-east at 14 to 16 km/h. The start, heading east to Woolwich, was into it on about 5 days in 10. Heading west, through Greenwich and along the Embankment, it was more often behind, on about 4 days in 10.

What is each section likely to feel like?

Each section with its usual race morning, hour by hour, timed for the 09:30 Sunday start and a steady 6:20 per km.

1. Blackheath to Woolwich

The three start lines meet just before mile 3, in Woolwich. The opening miles are on wide roads and net downhill, with a descent around mile 3. It's about 10° at the start, and heading east to Woolwich the north-easterly, about 14 km/h, was mostly in runners' faces on about 5 days in 10. This section was rated Tough on 2 days in 10, the most of any, with the Embankment.

2. Charlton, Greenwich and the Cutty Sark

West through Charlton and Greenwich, looping around the Cutty Sark between miles 6 and 7. It's about 11°, and as the course turns west the wind, about 15 km/h from the north-east, was more often behind, on about 4 days in 10. The heat stress is usually Low.

3. Deptford, Rotherhithe and Bermondsey to Tower Bridge

Through Deptford and Rotherhithe, onto Jamaica Road in Bermondsey and over Tower Bridge, just before halfway. The wind, about 14 km/h from the north-east, was more often against runners here, on about 4 days in 10, and Tower Bridge, high over the river, is more exposed than the records can show.

4. The Highway and the Isle of Dogs

East along The Highway to Westferry, then round the Isle of Dogs past Mudchute. About 12° past halfway, with the heat stress usually Low, and Moderate or more on about 1 day in 10.

5. Canary Wharf and Limehouse

Through Docklands and Canary Wharf, then Limehouse and Rainbow Row, just past mile 21. The wind, about 16 km/h from the north-east, was more often behind than against through Docklands, and this section was rated Good on 6 days in 10.

6. Tower Hill and the Embankment

The last five miles start back along The Highway to Tower Hill, then west along Victoria Embankment beside the Thames. Heading west along the river, the north-easterly, about 16 km/h, was more often behind runners, on about 4 days in 10, than against them, on about 3. This section was rated Good on 5 days in 10 and Tough on 2.

7. Westminster, Birdcage Walk and The Mall

Parliament Square, Birdcage Walk, the last corner in front of Buckingham Palace, and the finish on The Mall. It's about 13° at the finish on The Mall, with the north-easterly at about 16 km/h.

What should runners wear and pack for race day?

Layers for the start area, race kit for about 10–13°, and something for the wind. The organiser's course page has the route, the drinks stations and the toilets, and its Double FAQs have the start and cut-off times for each day. From the weather records:

• Old layers for the start. It was about 7° during the wait, 3° or colder on 1 morning in 10.
• Race kit for 10–13°. That's shorts and a light top for most runners, with gloves and arm sleeves you can drop.
• A cap or a light shell on wet days. Rain fell during the run on about 1 day in 10.
• Sunscreen on clear days. Heat stress reached Moderate on about 1 day in 10.

UK clocks went forward on 28 March 2027, so every time is British Summer Time. On the Saturday the finish line on The Mall closes at 17:30; on the Sunday the secondary finish line in Green Park stays open until 23:59.

When does the real forecast open?

Ten days before the race, in the RunFast app: on 14 April for Saturday runners and 15 April for Sunday runners. Load the course with your own pace and start time, and RunFast shows the heat and the wind at each stretch as you get there. From then on, trust the forecast over this preview.

How did we work this out?

The course was run again on every day from a week before to a week after 25 April, in each year from 2015 to 2024: 150 days. Each run started at the organiser's likely Sunday start, 09:30 British Summer Time, at a steady 6:20 per km, on that day's hourly Copernicus ERA5 weather, with its dew point and sunshine. Wave times for 2027 aren't out yet, and most of the field crosses the line later than the first start. RunFast's engine, the same one the app uses, worked out the heat stress and the weather's toll, and rated the run and each section. The start-area wait is the lowest temperature between 7:00 and the start, and a wet day has 1 mm of rain or more.

ERA5's grid cells are about 25 km across, so only a few cover this course. Streets, shelter, the river and the city's own warmth don't show. The course line is the organiser's official route on Strava (the 2026 route, from the Blackheath start), simplified; the organiser says the route is the same on both days in 2027. Historic weather, not a forecast.

Sources: London Marathon Events' TCS London Marathon home page, with the 2027 dates; its course page, event overview and 2027 Double FAQs; the organiser's official Strava route; ERA5 hourly time series (Hersbach et al., 2020). Contains modified Copernicus Climate Change Service information (2026). Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.