Marathon weather: what temperature is best for racing?
Updated
Weather is one of the biggest factors in marathon performance that you don’t control, but you can choose your race with it in mind.
Cool is fast
Studies of large city marathons have found that finishing times tend to be fastest in cool conditions, roughly 5–10°C, and get slower as it warms up. The effect is larger for slower runners, who spend longer on the course as the day heats up. Above about 20°C, most runners need to adjust their goal pace.
Humidity and sun make heat worse
Your body cools itself by evaporating sweat. In humid air that works less well, so 20°C and humid can feel harder than 24°C and dry. Full sun and little wind add to the load. That is why many races in warm places start before sunrise.
Which months are best?
Using 10 years of historical race-day weather for every marathon in our database, here is the share of each month’s marathons that usually start between 5 and 12°C:
| Month | Marathons | Starting at 5–12°C |
|---|---|---|
| January | 28 | 43% |
| February | 39 | 59% |
| March | 32 | 75% |
| April | 86 | 77% |
| May | 64 | 52% |
| June | 29 | 21% |
| July | 16 | 19% |
| August | 15 | 33% |
| September | 37 | 24% |
| October | 102 | 60% |
| November | 51 | 53% |
| December | 27 | 41% |
Spring and autumn dominate in the Northern Hemisphere, but the best conditions depend on the place: a winter marathon in a warm country can start cooler than a spring race inland.
How to use this when choosing a race
- Look at the typical start temperature and the peak during the race, not the monthly average.
- Check humidity: above about 80%, warm conditions get much harder.
- Use the temperature filter on the race finder, or see marathons with the best race-day weather.
Historical weather tells you what is likely, not what will happen. Check the forecast in race week and adjust your plan.