Running weather calculator
Enter the weather and your easy pace. Get a run score, how much the weather will cost your pace, the race heat flag and what to wear.
Working it out…
Estimates for planning easy runs, from the model in the ArcPace app. Not medical advice: in real heat, slow down by feel and stop if you feel unwell.
Want this for every hour of your forecast? ArcPace scores each hour 0–100, finds the best time to run today and tomorrow, and tells you what to wear. Free for iPhone. Get it on the App Store
What goes into it
- Dew point, the water in the air. Humid air slows the evaporation of sweat, your main way to shed heat.
- Temperature, and in the cold, the wind chill on top.
- Sun. Direct sun adds heat the thermometer misses, so full sun costs more than the same hour at dawn.
- Wind. A breeze helps in the heat and hurts in the cold.
- Rain, snow and thunder. Footing, cold rain, and lightning, which means don't run outside at all.
- Your pace. Slower runners lose more in the heat.
More in how much heat and humidity slow your pace, what to wear by temperature and WBGT and race heat flags.
Questions
How does the running weather calculator work?
It runs the same weather model as the ArcPace iPhone app. Temperature, dew point, sun, wind, rain and your own easy pace go in; a 0–100 run score, the seconds per mile the weather adds or saves, the race heat flag and what to wear come out.
Why does it ask for dew point, not humidity?
Dew point measures the water in the air directly; relative humidity changes with the temperature through the day. Dew point tells you far more about how a run will feel. Most weather apps show it.
Why does my pace matter?
Slower runners lose more time in the heat: they are out longer and make less cooling airflow. The calculator scales the cost to your easy pace.
Can it use my forecast?
The ArcPace app does: it scores every hour of your local forecast, finds the best time to run, and sends an evening note with tomorrow's best window. Free for iPhone.