ERA5 almanac comparison — 8 years of real data
Boundary Waters vs San Juan Islands: weather in August
Essentially a tie in August: Boundary Waters is 30% clear historically, San Juan Islands is 27% clear (8-year ERA5 average) — within the noise. Avg high 75°F vs 70°F. Boundary Waters also sees measurably more rain than San Juan Islands this month (41% vs 14% of days). Pick based on flight time or price, not weather — the weather won't decide this one for you.
Boundary Waters
MN
- Clear days, August
- 30%
- Sample size
- n=248 days
- Avg high
- 75°F
- Early August (1st–15th)
- 33%
- Late August (16th–end)
- 27%
- Rain frequency
- 41% of days
San Juan Islands
WA
- Clear days, August
- 27%
- Sample size
- n=248 days
- Avg high
- 70°F
- Early August (1st–15th)
- 33%
- Late August (16th–end)
- 22%
- Rain frequency
- 14% of days
Compare Boundary Waters vs San Juan Islands in another month
All percentages are historical averages from the ERA5 reanalysis via Open-Meteo, 8 full years (2018–2025). “Clear” means avg high ≥ 72 °F, precipitation < 1 mm, and a non-precipitation weather code. This is history, not a forecast. The live 7-day outlook for any destination is on its own page and may differ from the long-run average. Data from Open-Meteo.