Race-day weather · Wyndo for runners
Shamrock Shuffle weather
March 21, 2027 · Chicago, IL · scheduled start 8:30 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.
Countdown
205 days to race day
The live race-day forecast unlocks 199 days from now, when March 21, 2027 enters the 7-day forecast window — a start-time read for the scheduled 8:30 AM start. Until then, live hourly data is not available; the history below shows what race morning usually looks like.
Typical start temp
37°F
median of 6 years
A warm year
40°F
75th percentile start temp
Rain at the start
0%
0 of 6 measured years
Race-morning weather history
Late-March Chicago: cold and often windy (~35-48°F), lakefront wind chill, occasional snow/rain — typical-climate characterization, UNVERIFIED; ERA5 supplies actuals. 2020 CANCELLED (COVID); 2021 held in-person at reduced scale. No other cancellations 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
37°F
p75 (a warm year): 40°F
Median dew point
30°F
at the start hour
Rain at the start
0%
0 of 6 measured years
Warmest start
42°F
in 2026
Scroll sideways to see all columns.
| Year | Start temp | Dew point | Wind | Precip (start hr) | Day's high |
|---|---|---|---|---|---|
| 2026 | 42°F | 35°F | 20 mph | dry | 63°F |
| 2025 | 38°F | 26°F | 14 mph | dry | 47°F |
| 2024 | 34°F | 23°F | 9 mph | dry | 44°F |
| 2023 | 35°F | 30°F | 3 mph | dry | 42°F |
| 2022 | 33°F | 29°F | 5 mph | dry | 57°F |
| 2019 | 40°F | 32°F | 3 mph | dry | 46°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 8k
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.
Your race-day brief
Skip the taper-week refresh spiral. Email briefs for the Shamrock Shuffle: a start-hour outlook when race day enters the 7-day forecast window, updates only when it changes meaningfully, and a final look the day before.
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Race facts
- Start line
- Columbus Drive in Grant Park (start/finish near Columbus & Monroe), downtown Chicago — the classic Grant Park mass-race staging also used by the Chicago Marathon. Coordinate is an approximate geocode of Columbus Dr in Grant Park.
- Scheduled start
- 8:30 AM (America/Chicago) — Wheelchair 8:20 AM, Wave 1 (headline) 8:30 AM, Wave 2 9:00 AM. A scrape grabbing "9:00" catches only the second wave. Source: shamrockshuffle.com general-information [V].
- Field size
- 21,445 timed 8K finishers, 2025 (Webscorer results, verified) — the world's largest timed 8K. Day-of press figures (~28-30k 'runners and walkers') include untimed walkers; 32,500 is the participation cap.
- Registration
- open (participation capped at 32,500; sells out — Chicago running-season opener)
Wyndo is not affiliated with or endorsed by the Shamrock Shuffle (officially the "Bank of America Shamrock Shuffle 8K") 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.