Over the past 10 years, Chicago Marathon runners have faced temperatures ranging from 9\u00b0C (47\u00b0F) on cooler years to 23\u00b0C (73\u00b0F) in warmer editions. The median temperature of 16\u00b0C (61\u00b0F) puts this race in the challenging category for running conditions.
Wind speeds average 21 km/h during race hours, with peak gusts reaching 31 km/h in challenging years. Humidity sits around 69%, and there is a 60% chance of rain on race day.
These conditions translate to an estimated pace impact of +5.1% compared to ideal running conditions. For a 4-hour marathoner, that means roughly 12 minutes slower than a perfect-weather day.