ERA5 almanac comparison — 8 years of real data
Dallas vs Napa: weather in September
Napa is the clear winner for sun in September: 86% of days historically clear versus just 48% in Dallas — a 38-point gap across 8 years of ERA5 data. Dallas also sees measurably more rain than Napa this month (30% vs 4% of days). This isn't close.
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.
Dallas
TX
- Clear days, September
- 48%
- Sample size
- n=240 days
- Avg high
- 90°F
- Early September (1st–15th)
- 46%
- Late September (16th–end)
- 51%
- Rain frequency
- 30% of days
Napa
CA
- Clear days, September
- 86%
- Sample size
- n=240 days
- Avg high
- 86°F
- Early September (1st–15th)
- 93%
- Late September (16th–end)
- 79%
- Rain frequency
- 4% of days
Compare Dallas vs Napa 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.