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SunnyDays

ERA5 almanac — 8 years of real data

Houston in May

Houston in May is historically a poor month for sun: only 23% of days clear across 8 years (n=248, avg high 85°F). October is the clearest month for Houston historically. 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 Houston 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 Houston 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		 29% n=120 85°F
Late May
16th–end		 17% n=128 85°F
Full month average 23% n=248 85°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 Houston 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		 75% n=120
Late May
16th–end		 85% n=128
Full month average 80% n=248
10.8 h median sunshine per day 75% of days exceed 8 h sunshine 56% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 23%. Sunshine-based “warm & sunny”: 80%. The 57-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

Houston is mostly overcast in May historically: only 23% of days are clear across 8 years (n=248), avg high 85°F. If you want sun in Houston, October is historically much better. Most visitors this month will see more clouds than sun.

→ See all destinations in October — historically the best month for sun in Houston.

Every month in Houston

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

Historical clear-sky % for Houston, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 2% n=248 All destinations →
February 6% n=226 All destinations →
March 15% n=248 All destinations →
April 28% n=240 All destinations →
May ← this page 23% n=248 All destinations →
June 19% n=240 All destinations →
July 21% n=248 All destinations →
August 23% n=248 All destinations →
September 30% n=240 All destinations →
October 44% n=248 All destinations →
November 25% n=240 All destinations →
December 6% 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.