Race-day weather · Wyndo for runners
BOLDERBoulder weather
May 31, 2027 · Boulder, CO · traditional start around 6:45 AM (America/Denver) — not yet confirmed for 2027. What the start usually feels like, year by year — and a live start-time read once the race confirms its schedule and race week arrives.
Countdown
276 days to race day
The live race-day forecast unlocks 270 days from now, when May 31, 2027 enters the 7-day forecast window. Until then, live hourly data is not available; the history below shows what race morning usually looks like.
The 2027 schedule hasn't been published yet — both the date and start time shown here are carried from earlier editions and aggregators. We'll switch on the live start-time read when the race posts its schedule.
Typical start temp
48°F
median of 20 years
A warm year
51°F
75th percentile start temp
Rain at the start
5%
1 of 20 measured years
Race-morning weather history
Late-May Boulder mornings at ~5,300ft: cool starts (upper-40s to ~60F) with strong midday sun and afternoon thunderstorm potential — typical-climate characterization, UNVERIFIED; ERA5 supplies actuals. 2020 CANCELLED (COVID); 2021 held as a remote/virtual event (no mass in-person gun). Both are deterministic Memorial-Day slots and remain in history per slot-climatology, but 2021 had no in-person race. Wyndo tracks what this calendar slot has actually served up at the start hour — temperature, dew point, wind, and rain — including the years when weather canceled or disrupted the race, and reads the live forecast for the start once the race confirms its schedule and race week arrives.
Median start temp
48°F
p75 (a warm year): 51°F
Median dew point
42°F
at the start hour
Rain at the start
5%
1 of 20 measured years
Warmest start
54°F
in 2026
Scroll sideways to see all columns.
| Year | Start temp | Dew point | Wind | Precip (start hr) | Day's high |
|---|---|---|---|---|---|
| 2026 | 54°F | 42°F | 7 mph | dry | 79°F |
| 2025 | 49°F | 47°F | 0 mph | dry | 60°F |
| 2024 | 51°F | 37°F | 5 mph | dry | 75°F |
| 2023 | 50°F | 46°F | 7 mph | dry | 80°F |
| 2022 | 47°F | 43°F | 6 mph | dry | 63°F |
| 2021 | 46°F | 44°F | 1 mph | 0.7 mm | 60°F |
| 2020 | 35°F | 33°F | 7 mph | dry | 62°F |
| 2019 | 43°F | 41°F | 9 mph | dry | 62°F |
| 2018 | 52°F | 49°F | 1 mph | dry | 67°F |
| 2017 | 45°F | 41°F | 4 mph | dry | 65°F |
| 2016 | 46°F | 40°F | 7 mph | dry | 74°F |
| 2015 | 45°F | 43°F | 5 mph | dry | 64°F |
| 2014 | 49°F | 43°F | 6 mph | dry | 72°F |
| 2013 | 48°F | 40°F | 7 mph | dry | 80°F |
| 2012 | 47°F | 30°F | 7 mph | dry | 75°F |
| 2011 | 48°F | 42°F | 5 mph | dry | 64°F |
| 2010 | 42°F | 36°F | 5 mph | dry | 78°F |
| 2009 | 53°F | 48°F | 6 mph | dry | 65°F |
| 2008 | 51°F | 44°F | 3 mph | dry | 55°F |
| 2007 | 53°F | 44°F | 8 mph | dry | 79°F |
Slot climatology: each row is the weather at this race's usual calendar slot and start hour (ERA5 reanalysis at the start line) — including years when the edition was canceled or moved. A computed slot date is not a claim the race ran that day.
Your heat-adjusted goal for the 10k
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
- 30th Street just north of Walnut Street, Boulder; point is an approximate geocode of the 30th St / Walnut area (start arch not surveyed). Course finishes ~6.2mi away inside the University of Colorado's Folsom Field.
- Traditional start (not confirmed for 2027)
- 6:45 AM (America/Denver) — Headline = first citizen mass wave, 6:45am (Wave A), preceded by the Wheelchair Pro gun at 6:40am. Wave starts are staggered by predicted finish time across ~95 waves through ~9:15am — so a mid-pack runner starts much later than 6:45. Do NOT use the 11:15am elite Invitational gun as the mass start. Times carried from the 2026 schedule.
- Field size
- 45,055 FINISHERS in 2025; 52,185 REGISTRANTS (Wikipedia, re-verified live 2026-08-27) [V]. Page uses the finisher figure. Largest US 10K by finishers.
- Registration
- open (wave assignment by predicted 10K time / qualification)
Wyndo is not affiliated with or endorsed by the BOLDERBoulder (officially the "BOLDERBoulder 10K") 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.