The short answer
The best time to run in hot weather is usually the last hour before sunrise, when the air is coolest and the sun isn't up. Heat stress climbs fast after that: in Seville on 10 July 2023 it went from Low at 07:00 to High by 09:00. When a cool change arrives, the evening can be better.
Key takeaways
- Heat stress is usually lowest in the hour before sunrise, then climbs within two hours.
- Dawn often has the day's highest dew point, so cool air can still feel sticky.
- After a cool change or late cloud, the evening can beat the dawn.
- Check the hour-by-hour WBGT for your run, not the day's high.
On this page
- What is the best time to run in hot weather?
- How fast does the heat build after sunrise?
- Why isn't dawn always the coolest time?
- Is an evening run ever better than a morning one?
- How do you pick the right hour for tomorrow's run?
- What else lowers the heat on a hot-day run?
- Questions runners ask
- Sources and method
Words this guide uses
- WBGT (wet-bulb globe temperature)
- A heat-stress number that combines air temperature, humidity, sun and wind, used by race medical teams to set their flags.
- Cool change
- A shift to cooler, often drier air behind a front or a sea breeze, common in southern Australia's summer.
What is the best time to run in hot weather?
The best time to run in hot weather is usually the last hour before sunrise. The air is near its coolest and the sun isn't heating you yet, so heat stress is at its lowest.
The window is short, though, and on some days the evening is better. Here are five real summer days. It's part of our running weather forecast hub, and you can check your own run's hours in Map your run.
These are WBGT values from the ERA5 reanalysis, at three times of day, on summer days on four continents.
| Place and date | Before sunrise, WBGT °C (°F) | About two hours after sunrise, WBGT °C (°F) | Late evening, WBGT °C (°F) |
|---|---|---|---|
| Seville, Spain, 10 Jul 2023 | 07:00: 16.9 (62), Low | 09:00: 23.9 (75), High | 22:00: 24.7 (76), High |
| Houston, USA, 15 Aug 2023 | 06:00: 25.9 (79), High | 09:00: 30.2 (86), Extreme | 22:00: 26.5 (80), High |
| Brisbane, Australia, 15 Jan 2024 | 05:00: 22.1 (72), Moderate | 07:00: 25.8 (78), High | 22:00: 22.9 (73), High |
| Johannesburg, South Africa, 26 Dec 2023 | 05:00: 14.2 (58), Low | 07:00: 16.3 (61), Low | 22:00: 11.7 (53), Low |
| Melbourne, Australia, 17 Jan 2024 | 06:00: 19.3 (67), Moderate | 08:00: 20.2 (68), Moderate | 22:00: 13.5 (56), Low |
In three places, the hour before sunrise beat both mid-morning and late evening. In Johannesburg and Melbourne, the late evening was cooler still.
How fast does the heat build after sunrise?
Fast: within two hours of sunrise, heat stress often rises a whole level. The sun, not the air, does most of it.
Seville shows it clearly. At 07:00, before sunrise, the air was 21.8°C (71°F) and WBGT 16.9°C (62°F), Low. By 09:00 the air was 25.4°C (78°F), only 3.6°C (6.5°F) warmer, but WBGT had reached 23.9°C (75°F), High. By 10:00 it was 29.5°C (85°F), Extreme.
Notice, too, that 05:00 in Seville was warmer than 07:00: the air kept cooling until just before sunrise. Check the hourly forecast rather than setting an alarm by habit.
Why isn't dawn always the coolest time?
Because the weather doesn't always follow the daily cycle. A cool change, a band of cloud or a wind shift in the afternoon can make the evening cooler than the next or previous dawn.
Melbourne on 17 January 2024 is the clearest case. At 06:00 the air was 22.0°C (72°F) with a sticky dew point of 16.7°C (62°F), and WBGT was Moderate. Drier air arrived during the day. By 22:00 the air was 16.5°C (62°F), the dew point 9.9°C (50°F), and WBGT 13.5°C (56°F), Low.
In Johannesburg on 26 December 2023, cloud and a stiff wind arrived in the late afternoon. Heat stress fell from High at 13:00 to Low by 17:00, and kept falling into the night.
Dawn also brings the day's stickiest air in many humid places. In Houston on 15 August 2023, the dew point was 24.5°C (76°F) at 05:00 and 21.0°C (70°F) at 15:00. Cooler air, but more water in it.
Is an evening run ever better than a morning one?
Yes, when the forecast shows cooler or drier air arriving later in the day. On an ordinary hot day, though, the evening is usually worse than the dawn.
In Seville, the air at 22:00 was still 32.9°C (91°F), and WBGT was High. In Houston it was High too, at 26.5°C (80°F). The ground and buildings hold the day's heat, and the air cools slowly after sunset. In Brisbane, the evening's heat stress was close to the dawn's, but the dew point was higher.
So the evening wins only on certain days. A cool change or a storm can flip the order, and the hourly forecast shows which day it is.
How do you pick the right hour for tomorrow's run?
Compare the heat stress at the hours you could run, for the whole time you'll be out. Then pick the lowest, and make sure you finish before it climbs.
- Find sunrise. Your coolest window usually ends about an hour after it.
- Check the hourly WBGT for dawn, mid-morning and evening.
- Check the dew point. From 18°C (64°F) the air is hard work; from 21°C (70°F) it's oppressive.
- Count your run's length. A 90-minute run that starts at sunrise ends with the sun well up.
- Look for a change. A front or cloud later in the day can make the evening the better choice.
What else lowers the heat on a hot-day run?
Shade, a shorter route and an easier pace.
Shade matters most: in the RunFast engine, the sun alone adds about 5°C (9°F) to WBGT on a clear midday at 24°C (75°F). Run loops near home, so you can stop early if you need to.
Heat illness is serious. The American College of Sports Medicine's 2007 position stand says it can affect fit, healthy runners, and that early recognition and rapid cooling save lives. Race flags and medical advice override anything here. For the limits, see how hot is too hot to run, and for why your app's number reads low, see our guide to the feels like temperature for running.
Questions runners ask
Is it better to run in the morning or the evening in summer?
Usually the morning, if you can go before or just after sunrise. In three of the five places we checked, the pre-sunrise hour had lower heat stress than 22:00. The exceptions were Johannesburg and Melbourne, where cloud or drier air arrived later in the day. Check both hours in the forecast for your own run before deciding.
How long does the cool window last after sunrise?
Often only an hour or so. In Seville on 10 July 2023, heat stress went from Low before sunrise to Moderate by 08:00 and High by 09:00. In Brisbane on 15 January 2024 it reached High by 06:00, about an hour after sunrise. In Houston on 15 August 2023 it was Extreme by 08:00. Start early enough to finish before the sun is high.
How hot is too hot for a lunchtime run?
Midday in summer is usually the worst time, because the sun is highest. In Johannesburg on 26 December 2023, heat stress at 13:00 was High, a WBGT of 24.0°C (75°F), against Low before sunrise. The American College of Sports Medicine's 1996 race guidance set its highest risk band at 28°C (82°F). Move the run or keep it short and easy.
Does running in the shade lower heat stress?
Yes, a great deal. Shade takes away the sun's radiant heat, which is a large part of WBGT on a clear day. In the RunFast engine, 24°C (75°F) air at 70% humidity scores a WBGT of 26.0°C (79°F) in full midday sun and 21.0°C (70°F) without it. A tree-lined route or a shaded park can be worth the detour.
Is it safe to run in the heat if I'm used to it?
Being used to the heat helps, but it doesn't make you immune. The American College of Sports Medicine's 2007 position stand notes that exertional heatstroke can affect seemingly healthy athletes, and that being unacclimatised, dehydrated or recently ill raises the risk. If you feel dizzy, confused or stop sweating, stop and get help. This is not medical advice.
See the heat at your pace.
Drop in your route (GPX, FIT or TCX), pick the day and your pace, and see the feels like, dew point and heat stress for every kilometre, timed to when you’ll be there. Free, in your browser, no sign-up.
Sources and method
- Journal of Occupational and Environmental Hygiene (2008). Modeling the wet bulb globe temperature using standard meteorological measurements (Liljegren et al.)
- Copernicus Climate Change Service (ECMWF) (2026). ERA5 hourly data on single levels from 1940 to present
- Open-Meteo (2026). Historical weather API (ERA5)
- Medicine & Science in Sports & Exercise (American College of Sports Medicine) (2007). American College of Sports Medicine position stand: exertional heat illness during training and competition (Armstrong et al.)
- Medicine & Science in Sports & Exercise (American College of Sports Medicine) (1996). ACSM position stand: heat and cold illnesses during distance running
- US National Weather Service (La Crosse) (2026). Why dew point vs humidity
Hourly ERA5 reanalysis (Copernicus Climate Change Service, ECMWF) at the grid point nearest each city, fetched through Open-Meteo, in local time: Seville, Spain, 10 July 2023; Houston, USA, 15 August 2023; Brisbane, Australia, 15 January 2024; Melbourne, Australia, 17 January 2024; Johannesburg, South Africa, 26 December 2023. WBGT is the RunFast engine's Liljegren et al. (2008) model, with sunshine estimated from the sun's height and ERA5 cloud cover; dew point uses the Magnus formula. "Before sunrise" is the last whole hour with the sun below the horizon. The days were picked to show typical and unusual patterns, so they are examples, not averages. Reanalysis is a modelled grid, not a thermometer, and it ignores shade from buildings and trees. Imperial values are conversions.
Wes Thomson
Wes Thomson builds RunFast, which times the heat, humidity and dew point to a runner's own pace along the route, and its sister Windline, live wind forecasts for cyclists. Both run on the same forecast engine. He writes these guides with one focus: what the weather will do to your run, kilometre by kilometre, and how to plan around it.