Race-day weather · Wyndo for runners
Chicago Half Marathon weather
September 27, 2026 · Chicago, IL · scheduled start 7:00 AM (America/Chicago). What the start usually feels like, year by year — and a live start-time read once the race is inside the 7-day forecast window.
This edition has run
The 2026 Chicago Half Marathon is behind us
The next edition typically follows the race's pattern — Under Life Time (2023-present), the last Sunday of September — reproduces 2023-09-24, 2024-09-29, 2025-09-28, 2026-09-27 exactly. NOTE: older (pre-2023) editions were held earlier in September, so the current rule does NOT reproduce the full history — hence floating + a bounded historicalRaceDates list rather than a blind nth-weekday backfill.. We'll flip this page to the new date (and the live start-time read for race week) when the race confirms its schedule. The history below keeps the long view.
Race-morning weather history
Late-September Chicago lakefront: mild-to-warm (~55-72°F), lake humidity, occasional early-fall heat — typical-climate characterization, UNVERIFIED; ERA5 supplies actuals. 2020 CANCELLED (COVID). No other cancelled/virtual years found (search not exhaustive). Wyndo tracks what past editions of the race actually served up at the start hour — temperature, dew point, wind, and rain, and reads the live forecast for the start once race week arrives.
Median start temp
63°F
p75 (a warm year): 65°F
Median dew point
60°F
at the start hour
Rain at the start
0%
0 of 3 measured years
Warmest start
65°F
in 2024
Scroll sideways to see all columns.
| Year | Start temp | Dew point | Wind | Precip (start hr) | Day's high |
|---|---|---|---|---|---|
| 2025 | 63°F | 62°F | 5 mph | dry | 76°F |
| 2024 | 65°F | 60°F | 9 mph | dry | 71°F |
| 2023 | 58°F | 53°F | 6 mph | dry | 77°F |
Each row is the weather at a real past edition's date and this race's current start hour (ERA5 reanalysis at the start line).
Your heat-adjusted goal for the half marathon
The same cited model as the full calculator, pointed at this race: the median start-hour conditions this calendar slot has served up — climatology, not a forecast.
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Race facts
- Start line
- E. Hayes Drive in Historic Jackson Park (site of the 1893 World's Columbian Exposition, near the Museum of Science and Industry); out-and-back up the lakefront. Coordinate is a Nominatim geocode of E. Hayes Dr — approximate.
- Scheduled start
- 7:00 AM (America/Chicago) — Half 7:00 AM, Para-athlete half start 6:57 AM, 5K 7:45 AM. Source: chicagohalfmarathon.com/half-marathon (2026) [V].
- Field size
- fieldSize is 2023 half-marathon finishers (7,253, Webscorer) [V]. The scout's "~15-18k" was NOT carried — that figure conflates distances/registrants: FOX32 reported ~10,000 total participants across half+5K in 2024, and half-only finishers run ~7-7.5k. Recent editions (2024/2025) sold out at similar scale; historic high was 13,537 half finishers in 2009. OPEN QUESTION: a current half-only finisher count (2024/2025) if a cleaner source surfaces.
- Registration
- open (Special Events Management / RunSignup; recent editions sold out)
Wyndo is not affiliated with or endorsed by the Chicago Half Marathon (officially the "Life Time Chicago Half Marathon") or its organizers. Race names are used descriptively to identify the event; schedules and start times belong to the race — always confirm details on the official site. Weather guidance here is informational, never medical advice, and event alert flags on race day belong to the race's own medical team.