Skip to main content
SunnyDays

ERA5 almanac — 8 years of real data

Dallas in May

Dallas in May is historically a poor month for sun: only 36% of days clear across 8 years (n=248, avg high 84°F). 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 May

Clear-sky percentage for Dallas in May, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early May
1st–15th		 42% n=120 84°F
Late May
16th–end		 30% n=128 84°F
Full month average 36% n=248 84°F

Sunshine & warmth in May

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 May. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early May
1st–15th		 82% n=120
Late May
16th–end		 86% n=128
Full month average 84% n=248
11.2 h median sunshine per day 74% of days exceed 8 h sunshine 42% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 36%. Sunshine-based “warm & sunny”: 84%. The 48-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 is mostly overcast in May historically: only 36% of days are clear across 8 years (n=248), avg high 84°F. Most visitors this month will see more clouds than 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 ← this page 36% n=248 All destinations →
June 38% n=240 All destinations →
July 47% n=248 All destinations →
August 54% n=248 All destinations →
September 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.