ERA5 almanac comparison — 8 years of real data
Hartford vs Whitefish: weather in September
Essentially a tie in September: Hartford is 38% clear historically, Whitefish is 38% clear (8-year ERA5 average) — within the noise. Avg high 75°F vs 70°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 September. For this
week’s actual forecast, each destination links to its live page below.
Hartford
CT
- Clear days, September
- 38%
- Sample size
- n=240 days
- Avg high
- 75°F
- Early September (1st–15th)
- 40%
- Late September (16th–end)
- 36%
Whitefish
MT
- Clear days, September
- 38%
- Sample size
- n=240 days
- Avg high
- 70°F
- Early September (1st–15th)
- 55%
- Late September (16th–end)
- 20%
Compare Hartford vs Whitefish 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.