ERA5 almanac comparison — 8 years of real data
Crater Lake vs San Juan Islands: weather in December
Essentially a tie in December: Crater Lake is 0% clear historically, San Juan Islands is 0% clear (8-year ERA5 average) — within the noise. Avg high 35°F vs 45°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 December. For this
week’s actual forecast, each destination links to its live page below.
Crater Lake
OR
- Clear days, December
- 0%
- Sample size
- n=248 days
- Avg high
- 35°F
- Early December (1st–15th)
- 0%
- Late December (16th–end)
- 0%
San Juan Islands
WA
- Clear days, December
- 0%
- Sample size
- n=248 days
- Avg high
- 45°F
- Early December (1st–15th)
- 0%
- Late December (16th–end)
- 0%
Compare Crater Lake 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.