Free tool
Race-day weather.
The forecast six days out, your goal time adjusted for the heat, and every race morning since 2000, measured. For the NYC, Chicago, Boston, Philadelphia and California International marathons.
Chicago MarathonSunday, October 11, 2026113Race day at the startSlight penalty: 0.5% to 1% slower
NYC MarathonSunday, November 1, 202683Typical startNo adjustment needed
Philadelphia MarathonSunday, November 22, 202673Typical startNo adjustment needed
California International MarathonSunday, December 6, 202683Typical startNo adjustment needed
Boston MarathonMonday, April 19, 202784Typical startNo adjustment needed
What each page gives you
- The forecast, six days out. Temperature and dew point at the start and through the morning, from the National Weather Service, refreshed twice a day until the gun.
- Your goal time, adjusted. Each goal is averaged across the hours you'll actually be running, so a later wave gets the warmer number it deserves.
- Every race morning since 2000. Measured, not remembered: a long-record NOAA weather station near the course, at the hour of today’s first-wave start and three hours later. The data downloads as a CSV.
- The day after. What race day actually was, and what your finish time was worth on a cool day.
The score itself is simple. Add the air temperature to the dew point, both in Fahrenheit, and read off the slowdown band below. It's the same method as my heat pace calculator, which has the full chart.
Combined score → how much to slow down
- 100 or lessNo pace adjustment
- 101 – 1100% to 0.5% slower
- 111 – 1200.5% to 1% slower
- 121 – 1301% to 2% slower
- 131 – 1402% to 3% slower
- 141 – 1503% to 4.5% slower
- 151 – 1604.5% to 6% slower
- 161 – 1706% to 8% slower
- 171 – 1808% to 10% slower
- Above 180Hard running is not recommended
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Want race week planned around you?
A forecast adjusts a pace. It doesn't know your training, how you handle heat, or how your last long run went. I write every plan by hand and set race-week pacing with each athlete. It starts with a free 20-minute call.
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RunFitCoach is not affiliated with any of these races or their organizers. Forecasts from the National Weather Service. Observations from NOAA/FAA ASOS stations via the Iowa Environmental Mesonet.