An evening 10K from City Hall along the Rideau Canal on the Saturday of Tamarack Ottawa Race Weekend. Late-May evenings are usually mild, but after a hot day the warmth stays in the streets.
Plan for about 69°F (21°C) at the 18:00 start, feeling like 68°F (20°C), with 64% humidity and 5 mph wind, warming to roughly 69°F (21°C) by the finish. It rained on 4 of the last 10 race days. Wear: Singlet or Tank, Running Shorts, Running Cap, Waterproof Jacket.
Feels like 68°F (20°C) at the start · finish 69°F (21°C) · rain 4 of 10 · start air from 52°F (11°C) to 86°F (30°C)
Conditions at the 18:00 start on the race's usual date each year (saturday of Ottawa Race Weekend (late May)). Years when the race was cancelled or moved still show that date's weather. Source: Open-Meteo ERA5 archive.
Bar: air temperature from start to finish · dot: feels-like effective temperature · ≫ windy (15+ mph) · rain · shaded: PR band 40–50°F
| Year | Start temp | Feels like | Finish | Humidity | Wind | Rain | Sky |
|---|---|---|---|---|---|---|---|
| 2025 | 52°F (11°C) | 49°F | 52°F | 81% | 4 mph | 0.16 in | Drizzle |
| 2024 | 62°F (17°C) | 62°F | 62°F | 72% | 2 mph | – | Overcast |
| 2023 | 76°F (24°C) | 78°F | 76°F | 56% | 3 mph | – | Clear |
| 2022 | 68°F (20°C) | 66°F | 68°F | 57% | 6 mph | 0.10 in | Overcast |
| 2021 | 77°F (25°C) | 79°F | 77°F | 66% | 8 mph | – | Mostly clear |
| 2020 | 74°F (23°C) | 67°F | 74°F | 22% | 8 mph | – | Clear |
| 2019 | 58°F (14°C) | 60°F | 58°F | 100% | 3 mph | 0.62 in | Rain |
| 2018 | 69°F (21°C) | 72°F | 69°F | 80% | 4 mph | 0.11 in | Overcast |
| 2017 | 65°F (18°C) | 63°F | 65°F | 66% | 6 mph | – | Clear |
| 2016 | 86°F (30°C) | 88°F | 86°F | 41% | 3 mph | – | Overcast |
Coldest start: 52°F (11°C) in 2025. Warmest: 86°F (30°C) in 2016. Wettest: 0.62 in in 2019.
The time estimates apply published temperature–performance curves to this race's ten-year weather history. Performance peaks at an effective race temperature of roughly 40 to 50°F and degrades faster the warmer it gets and the slower you run (Ely et al., 2007; El Helou et al., 2012). Wind adds a cost that grows with the square of the wind speed (Pugh, 1971), split into head and tail components on point-to-point courses. Shorter races are penalised less. This is a model, not a prediction; your training and the course matter more.
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Built from the 10-year average start conditions by the same engine as the live tool. Treat optional items as corral-only layers you can shed.
Singlet or Tank
Maximum breathability for hot conditions
Waterproof Jacket
Breathable rain protection
Running Shorts
Lightweight with built-in brief
Running Cap
Keep rain out of eyes
Trail or Waterproof Shoes
Better grip and water resistance
✓ Worn by the author
Fast-drying micromesh tee for warm-weather miles
$75
✓ Worn by the author
Packable, washable running cap with a short brim
$55
The gold standard short sleeve for everyday running
$85
✓ Worn by the author
Thin, ribbed quarter sock that keeps grit out
$36
Water-resistant, reef-safe — non-negotiable for outdoor runs
$16
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Over 2016 to 2025 the start averaged 69°F (21°C) (feels like 68°F (20°C)) with 64% humidity and 5 mph wind, warming to about 69°F (21°C) by the finish. It rained measurably on 4 of those 10 race days. The coldest start was 52°F (11°C) in 2025; the warmest was 86°F (30°C) in 2016.
For a typical 69°F (21°C) start: Singlet or Tank, Running Shorts, Running Cap, Waterproof Jacket. Dress for about 15°F warmer than the start temperature, since the race itself adds that much, and plan to shed anything you only need in the corral.
The Ottawa 10K is usually held on saturday of Ottawa Race Weekend (late May). The next expected date is Saturday, May 22, 2027. Confirm on the official site, since dates occasionally move.
The live forecast on this page comes from Open-Meteo and unlocks 16 days before the race. Forecasts inside 7 days are reliable for temperature within a few degrees; rain timing firms up in the last 2 to 3 days. Until then, the 10-year history above is the best planning guide.
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