Skip to main content
SunnyDays

ERA5 almanac — 8 years of real data

Nashville in September

Nashville in September is a mixed month for sun: 48% of days historically clear (n=240, avg high 83°F). The outcome varies year to year — check the early/late split below. Historical average, not a forecast.

What you are reading: 8-year historical averages from the ERA5 reanalysis, not a forecast. A month that is historically 90% clear can still be overcast on your specific trip. For this week’s actual forecast, see the live Nashville page. Both can be true at once: “historically strong in this month; this particular week is not.” We label which is which.

Early vs. Late September

Clear-sky percentage for Nashville in September, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early September
1st–15th		 48% n=120 83°F
Late September
16th–end		 47% n=120 83°F
Full month average 48% n=240 83°F

Sunshine & warmth in September

A second measure using actual sunshine hours (ERA5 sunshine_duration), not the daily weather code. A Lowcountry day with 12 hours of sun and a 25-minute afternoon storm is counted below as a warm, sunny day — because it was. How we define this.

Sunshine-based metrics for Nashville in September. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early September
1st–15th		 87% n=120
Late September
16th–end		 81% n=120
Full month average 84% n=240
11.5 h median sunshine per day 80% of days exceed 8 h sunshine 32% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 48%. Sunshine-based “warm & sunny”: 84%. The 36-point gap is from brief afternoon convective storms that stamp the whole day as “rain” in the WMO code but leave the bulk of the sunshine untouched.

Bottom line

Nashville in September is genuinely mixed: 48% of days historically clear (n=240), avg high 83°F — roughly even odds. The outcome varies year to year; don't book if you need guaranteed sun.

Every month in Nashville

Compare across all months with data. Numbers are historical clear-sky %.

Historical clear-sky % for Nashville, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 1% n=226 All destinations →
March 8% n=248 All destinations →
April 18% n=240 All destinations →
May 28% n=248 All destinations →
June 30% n=240 All destinations →
July 19% n=248 All destinations →
August 32% n=248 All destinations →
September ← this page 48% n=240 All destinations →
October 32% n=248 All destinations →
November 6% n=240 All destinations →
December 0% n=248 All destinations →

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.