Race-day weather · Sunday, October 11, 2026

Chicago Marathon weather.

Race day came in at 60°F with a 53°F dew point at the 7:35am start, a combined score of 113, and 122 three hours in. For a 3:30 runner in the first wave, it cost 0.5% to 1%. If your time felt slow, here is what it was worth on a cool day.

113 Combined score
at the start Measured on race day: 60°F air + 53°F dew point at the 7:35am start (reading taken at 7:53am), Chicago Midway weather station. Slight penalty: 0.5% to 1% slower at the start.
Start · 7:35am11360° air · 53° dew point
+2 hours · 9:35am12065° air · 55° dew point
+4 hours · 11:35am12670° air · 56° dew point

What your finish time was worth on a cool day

Find your finish time on the left. The weather’s cost is averaged across the hours you were on course, so pick the column for the wave you started in.

Your finish timeStarting 7:35amStarting 8:35am
2:452:43 to 2:440.5% to 1% faster · score 1182:42 to 2:431% to 2% faster · score 121
3:002:58 to 2:590.5% to 1% faster · score 1182:56 to 2:581% to 2% faster · score 121
3:153:13 to 3:140.5% to 1% faster · score 1193:11 to 3:131% to 2% faster · score 122
3:303:28 to 3:290.5% to 1% faster · score 1193:26 to 3:281% to 2% faster · score 123
3:453:43 to 3:440.5% to 1% faster · score 1193:41 to 3:431% to 2% faster · score 123
4:003:58 to 3:590.5% to 1% faster · score 1203:55 to 3:581% to 2% faster · score 123
4:304:25 to 4:271% to 2% faster · score 1214:25 to 4:271% to 2% faster · score 124
5:004:54 to 4:571% to 2% faster · score 1214:54 to 4:571% to 2% faster · score 125
What I’d take from it

Credit yourself the 0.5% to 1%. A slower watch on a morning like that is the same fitness as a faster one on a cool day, so set your next training paces from the cool-day equivalent, not the clock. Plug that time into the pace calculator and it gives you the paces.

Get my race-week notes

How I adjust pacing, fueling and the warm-up when race morning runs warm. One email when a new training note drops. No spam, unsubscribe anytime.

Almost in. Check your inbox to confirm your email.

Chicago Marathon weather on race morning since 2000

Every row in the table below is a measurement from the Chicago Midway weather station, taken nearest 7:35am (today’s first-wave start) and again three hours later. Start times have moved over the years, so treat 7:35am as a clock time, not always the gun. Across 26 race mornings:

  • A typical 7:35am reading is 52°F with a 45°F dew point, a combined score of 97.
  • The warmest was 2021: 72°F with a 61°F dew point at 7:35am, a score of 133.
  • The most humid was 2007, with a 65°F dew point.
  • The coldest was 2009, at 32°F.
  • On 10 of 26 race mornings the 7:35am score was above 100, enough to call for a pace adjustment. Three hours later, 14 of 26 were.
Chicago Marathon race mornings · air / dew point (°F) and combined score
YearDateAir / dew at 7:35amScoreAir / dew at 10:35amScore
2026Oct 1160° / 53°11367° / 55°122
2025Oct 1252° / 47°9962° / 48°110
2024Oct 1360° / 53°11361° / 51°112
2023Oct 847° / 37°8453° / 34°87
2022Oct 947° / 32°7960° / 36°96
2021Oct 1072° / 61°13375° / 61°136
2020–Virtual only (COVID-19), no race morning
2019Oct 1342° / 32°7448° / 31°79
2018Oct 759° / 56°11560° / 56°116
2017Oct 857° / 54°11169° / 55°124
2016Oct 951° / 45°9658° / 43°101
2015Oct 1154° / 44°9868° / 48°116
2014Oct 1246° / 37°8357° / 40°97
2013Oct 1348° / 39°8760° / 38°98
2012Oct 739° / 28°6748° / 24°72
2011Oct 960° / 49°10973° / 50°123
2010Oct 1061° / 50°11175° / 48°123
2009Oct 1132° / 22°5438° / 21°59
2008Oct 1264° / 56°12075° / 55°130
2007Oct 772° / 65°13782° / 67°149
2006Oct 2240° / 35°7541° / 34°75
2005Oct 952° / 43°9555° / 43°98
2004Oct 1050° / 45°9559° / 41°100
2003Oct 1249° / 45°9461° / 42°103
2002Oct 1340° / 27°6744° / 23°67
2001Oct 736° / 29°6547° / 20°67
2000Oct 2254° / 48°10262° / 51°113

Readings from the Chicago Midway ASOS weather station (NOAA/FAA, via the Iowa Environmental Mesonet), the observation nearest each hour. Scores above 100 call for a pace adjustment. Download every hour as a CSV.

How the score works

Add the air temperature to the dew point, both in Fahrenheit. That combined score is closer to what your body feels than the temperature alone, because dew point decides whether your sweat can evaporate, and evaporating sweat is how you shed heat at race pace. The bands below are the same ones my heat pace calculator uses, and that page has the full chart and the physiology behind it.

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

The bands are a coach's rule of thumb, not a lab measurement. Treat each range as a starting point and let effort make the final call.

Want the next one built 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.

Book a free intro call

Other race-day weather pages

NYC MarathonSunday, November 1, 202683Typical startNo adjustment needed Boston MarathonMonday, April 19, 202784Typical startNo adjustment needed Philadelphia MarathonSunday, November 22, 202673Typical startNo adjustment needed California International MarathonSunday, December 6, 202683Typical startNo adjustment needed

All race-day weather pages

RunFitCoach is not affiliated with the Bank of America Chicago Marathon or its organizers. Observations from the Chicago Midway ASOS station (NOAA/FAA) via the Iowa Environmental Mesonet. Data updated Tuesday, October 13, 2026.

Heat is one variable. I plan for all of them.

Free intro call, twenty minutes. No payment until we both say yes.

Book your intro call
Prefer to apply in writing? Start here