ERA5 almanac comparison — 8 years of real data
San Juan Islands vs Sun Valley: weather in May
Essentially a tie in May: San Juan Islands is 3% clear historically, Sun Valley is 3% clear (8-year ERA5 average) — within the noise. Avg high 61°F vs 59°F. Pick based on flight time or price, not weather — the weather won't decide this one for you.
What you are reading: 8-year historical averages, not a forecast.
Either destination can still surprise you this specific May. For this
week’s actual forecast, each destination links to its live page below.
San Juan Islands
WA
- Clear days, May
- 3%
- Sample size
- n=248 days
- Avg high
- 61°F
- Early May (1st–15th)
- 4%
- Late May (16th–end)
- 2%
Sun Valley
ID
- Clear days, May
- 3%
- Sample size
- n=248 days
- Avg high
- 59°F
- Early May (1st–15th)
- 0%
- Late May (16th–end)
- 6%
Compare San Juan Islands vs Sun Valley 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.