Heat & Air Check

Hour by hour, how hard London's heat will be today — the easier windows named, and the official heat-health alert for the city.

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About these tools

Town Tools builds free, public tools for London and towns around the world. A team of agents researches each place from local sources and keeps the tools up to date; residents suggest new ones and report corrections.

Day

Best windows

Peak feels-like

Peak air

Tuesday 13 October

all day

18°C

36 · Good

Wednesday 14 October

all day

15°C

42 · Good

How this page decides

Heat uses the National Weather Service’s heat-index categories, applied to the modelled feels-like temperature: Caution 27°C–32°C, Extreme Caution 32°C–39°C, Danger 39°C–51°C, Extreme Danger 52°C and up.

Air uses the US EPA air quality index: Good 0–50, Moderate 51–100, Unhealthy for Sensitive Groups 101–150, Unhealthy 151–200, Very Unhealthy 201–300, Hazardous above that. The number here is that same EPA index, computed by Open-Meteo from the Copernicus CAMS model.

Each hour takes the harder of the two constraints, and the strip says which one. A “best window” means hours where the feels-like temperature stays below 27°C (below the NWS Caution band) and the air is no worse than Moderate — the EPA’s general-population activity cautions start at 101. No thresholds on this page are ours.

Reading it for your plans

Getting across town

The deep Tube lines have no cooling on much of the network and run hotter than the street, so the middle of a hot afternoon is the hardest time to travel underground. Carry water on the Central, Bakerloo, Northern, Piccadilly and Victoria lines especially, and read the strip for the hours you'll actually be out.

Flats, older neighbours and young children

London's heat is often worst overnight and indoors — top-floor and single-aspect flats hold the day's heat long after dark. The city set the UK's highest-ever overnight temperature during the July 2022 heat, so a 'tropical night' is a real London thing. If you check on anyone, the evening and small hours are when it matters most.

Parks, lidos and working outside

The parks and lidos are the city's cool space by day but the most exposed places at midday. If you're gardening, on a site, cycling a long way or spending the day outdoors, treat the number here as a floor, not a ceiling, and read it against the whole day — the early window usually wins.

Worth knowing

London's heat record

London's highest temperature ever was 40.2°C, reached at both Heathrow and St James's Park on 19 July 2022 — the first time the capital passed 40°C. (The UK record of 40.3°C was set the same day at Coningsby in Lincolnshire.) That same night London also set the UK's highest-ever overnight low, 25.8°C at Kenley — a genuinely tropical night. Most summer days are nowhere near this; the question is usually which hours are easier, and on the extreme days this page will say none are.

Source: Met Office — record high temperatures verified (July 2022), checked 6 July 2026

The city makes its own heat

Central London runs several degrees warmer than the countryside around it, strongest at night and in the places with least greenery — the urban heat island. Brick, concrete and tarmac soak up the day's sun and give it back after dark, which is why an inner-London night can stay uncomfortable long after a rural one has cooled. It's also why the heat is measurably harder on health here than the raw forecast suggests.

Source: The potential of urban trees to reduce heat-related mortality in London (peer-reviewed), checked 6 July 2026

The official channels

Met Office — London hour-by-hour forecastThe official forecast for Greater London, including any heat warnings.

Heat-Health Alerts — the live map (UKHSA & Met Office)The official yellow / amber / red heat-health alert for London — the authoritative signal of a health-relevant heatwave.

What the heat-health alert levels mean (Met Office)Green, yellow, amber and red — who each level is a risk to.

NHS — coping in hot weatherStaying well in the heat, and the signs of heat exhaustion and heatstroke.