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SunnyDays

ERA5 almanac — 8 years of real data

Dallas in September

Dallas in September is a mixed month for sun: 48% of days historically clear (n=240, avg high 90°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 Dallas 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 Dallas 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		 46% n=120 90°F
Late September
16th–end		 51% n=120 90°F
Full month average 48% n=240 90°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 Dallas 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		 95% n=120
Full month average 91% n=240
11.7 h median sunshine per day 85% of days exceed 8 h sunshine 30% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 48%. Sunshine-based “warm & sunny”: 91%. The 43-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

Dallas in September is genuinely mixed: 48% of days historically clear (n=240), avg high 90°F — roughly even odds. The outcome varies year to year; don't book if you need guaranteed sun.

Every month in Dallas

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

Historical clear-sky % for Dallas, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 3% n=248 All destinations →
February 11% n=226 All destinations →
March 23% n=248 All destinations →
April 33% n=240 All destinations →
May 36% n=248 All destinations →
June 38% n=240 All destinations →
July 47% n=248 All destinations →
August 54% n=248 All destinations →
September ← this page 48% n=240 All destinations →
October 49% n=248 All destinations →
November 21% n=240 All destinations →
December 9% 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.