ERA5 almanac comparison — 8 years of real data
Lisbon vs Rome: weather in September
Lisbon edges out Rome for sun in September: 66% clear historically versus 50% (8-year ERA5 average, a 16-point gap). Both are viable — Lisbon 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.
Lisbon
PT
- Clear days, September
- 66%
- Sample size
- n=240 days
- Avg high
- 80°F
- Early September (1st–15th)
- 69%
- Late September (16th–end)
- 63%
Rome
IT
- Clear days, September
- 50%
- Sample size
- n=240 days
- Avg high
- 82°F
- Early September (1st–15th)
- 61%
- Late September (16th–end)
- 38%
Compare Lisbon vs Rome 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.