Skip to main content
SunnyDays

ERA5 almanac — 8 years of real data

Birmingham in September

Birmingham in September: 31% of days see measurable rain, 86°F average high, 49% of days historically clear (n=240, ERA5 2018–2025).

Birmingham in September is a mixed month for sun: 49% of days historically clear (n=240, avg high 86°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 Birmingham 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 Birmingham 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		 44% n=120 86°F
Late September
16th–end		 54% n=120 86°F
Full month average 49% n=240 86°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 Birmingham 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		 93% n=120
Late September
16th–end		 86% n=120
Full month average 90% n=240
11.6 h median sunshine per day 86% of days exceed 8 h sunshine 31% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 49%. Sunshine-based “warm & sunny”: 90%. The 41-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

Birmingham in September is genuinely mixed: 49% of days historically clear (n=240), avg high 86°F — roughly even odds. The outcome varies year to year; don't book if you need guaranteed sun.

Every month in Birmingham

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

Historical clear-sky % for Birmingham, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 0% n=248 All destinations →
February 1% n=226 All destinations →
March 9% n=248 All destinations →
April 27% n=240 All destinations →
May 36% n=248 All destinations →
June 30% n=240 All destinations →
July 17% n=248 All destinations →
August 28% n=248 All destinations →
September ← this page 49% n=240 All destinations →
October 44% n=248 All destinations →
November 14% n=240 All destinations →
December 1% n=248 All destinations →

Frequently asked

Does it rain in Birmingham in September?

Sometimes. Birmingham sees measurable rain on 31% of days in September historically (n=240 days, ERA5 2018–2025) — not frequent enough to plan around, but not negligible either.

Is Birmingham good for sun in September?

It's mixed. Birmingham in September is clear on 49% of days historically (avg high 86°F, n=240 days, ERA5 2018–2025) — the outcome varies year to year.

How Birmingham compares in September

Head-to-head clear-sky comparisons against destinations travelers plausibly weigh against Birmingham this month — same passport tier, similar flight distance, both sides from the same 8-year ERA5 record.

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.