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.

About these tools

Summer plans in London get made around the heat — a commute across town, a day in the park, a lido session, checking on an older neighbour. This page reads the hourly heat and air forecasts together and names the easier hours. On the genuinely extreme days no hour is good, and it will say so.

Today, Monday 24 August

Best windows today: all day.

As of 24 August at 2:51. Modelled forecast for the area around central London, refreshed about every half hour.

Hour by hour today

5 am–11 pmComfortableNothing flagged on either scale.

UV peaks near 5 today. On the EPA’s UV index scale, 1–2 is low; 8 and above is very high to extreme and calls for extra sun protection.

The next two days

Day	Best windows	Peak feels-like	Peak air
Tuesday 25 August	all day	23°C	50 · Good
Wednesday 26 August	all day	24°C	57 · Moderate

Guidance, not a medical call

Heat lands differently person to person — age, pregnancy, some medications, working outdoors, and conditions like asthma all change the math. This page only ever says easier or harder, never “safe.” For health guidance see the official heat-safety pages, and for official readings use the channels listed below.

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 2026-07-06

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 2026-07-06

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.

For the fuller air picture — pollutant by pollutant, with the local context — Pollen & Air Quality — the hot, still days are often the higher-pollen, higher-pollution ones too. The two pages band air on different scales: this one uses the US EPA index, that one uses the European index, so the numbers will not match.

Fetched 24 August at 2:51. These are modelled estimates for the area around central London, not measurements — a shadeless trail at 3 pm runs hotter than the area-wide number. Weather and air-quality data by Open-Meteo (CC BY 4.0); air quality based on Copernicus CAMS. Heat categories from the National Weather Service; air bands from the US EPA.