Marathon Weather Forecast

Enter the race city, the date and your start time, and the checker scores the first 3 hours of your run.

What matters most for a marathon

For a marathon, heat counts 1.6 times and humidity 1.4 times. Above 32 °C the checker adds 3.2 points and above 38 °C 6.4. Humidity adds 1.4 points above 60% and 2.8 above 80%, because humid air makes it harder for the body to cool down. Rain counts only 0.7 times (3.5 points at a 50% chance) and wind 0.8 times.

The same temperature rule also counts cold: 1.6 points below 10 °C and 4.8 below 5 °C, even though many runners like a cool start. A mild, dry and not too humid morning therefore scores best. Up to 3 is low risk, up to 6 moderate and above 6 high.

Worked example: a race at 34 °C with 70% humidity, 10% chance of rain and 10 km/h of wind gives 0.7 + 0 + 3.2 + 1.4 = 5.3 points, a moderate risk. At 22 °C and 55% humidity the same race scores 0.7 (low): heat and humidity make the difference.

Best and worst race months in 10 cities

Marathon risk for an average day in each month, from the 2006–2025 averages (chance of rain = rainy days divided by 30, typical afternoon high and humidity, no wind). Most races start in the morning, when it is cooler than this.

City	Lowest risk	Highest risk
Lisbon	July · 2 (low)	December · 5.8 (moderate)
Rome	July · 3.1 (moderate)	November · 6.3 (high)
Barcelona	July · 3.4 (moderate)	September · 4.9 (moderate)
Madrid	September · 1.5 (low)	January · 5.2 (moderate)
Paris	September · 4.4 (moderate)	January · 8.1 (high)
London	September · 4.6 (moderate)	January · 8 (high)
Amsterdam	April · 5 (moderate)	November · 8.6 (high)
Berlin	September · 4.5 (moderate)	January · 10 (high)
Vienna	March · 4.3 (moderate)	December · 10 (high)
New York	November · 3.3 (moderate)	January · 8.3 (high)

The lowest risk is in Madrid in September (1.5). 2 of 10 cities have at least one low-risk month. In the hottest months heat and humidity add the points, in winter the cold rule does.

Race day weather checklist

Set the time to your start and look at the 3 hours after it.
Above 60% humidity, plan a slower pace and drink more.
If the checker shows a cooler window earlier, ask whether your wave can start then.
Check the forecast again 2–3 days before for a reliable picture.

FAQ

What is the ideal weather for a marathon?

Mild and dry with low humidity: between 10 and 32 °C the temperature adds nothing, and below 60% humidity adds nothing either.

Why does humidity matter so much for runners?

Humid air slows down cooling by sweat. For marathons the checker counts humidity 1.4 times: 1.4 points above 60% and 2.8 above 80%.

Does rain affect the marathon risk?

A little. Rain counts only 0.7 times for a marathon, so a 50% chance adds 3.5 points, less than for a wedding or a festival.

How far ahead can I check race-day weather?

Up to 10 days ahead with the hourly forecast; for later dates use the monthly table above.