ERA5 almanac comparison — 8 years of real data
Sonoma vs Tucson: weather in September
Sonoma edges out Tucson for sun in September: 86% clear historically versus 70% (8-year ERA5 average, a 16-point gap). Both are viable — Sonoma is the safer bet.
What you are reading: 8-year historical averages, not a forecast.
Either destination can still surprise you this specific September. For this
week’s actual forecast, each destination links to its live page below.
Sonoma
CA
- Clear days, September
- 86%
- Sample size
- n=240 days
- Avg high
- 84°F
- Early September (1st–15th)
- 92%
- Late September (16th–end)
- 81%
Tucson
AZ
- Clear days, September
- 70%
- Sample size
- n=240 days
- Avg high
- 96°F
- Early September (1st–15th)
- 72%
- Late September (16th–end)
- 69%
- Rain frequency
- 20% of days
Compare Sonoma vs Tucson 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.