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SunnyDays

ERA5 almanac — 8 years of real data

San Antonio in May

San Antonio in May is historically a poor month for sun: only 26% of days clear across 8 years (n=248, avg high 88°F). October is the clearest month for San Antonio 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 San Antonio 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 San Antonio 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		 31% n=120 88°F
Late May
16th–end		 22% n=128 88°F
Full month average 26% n=248 88°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 San Antonio 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		 80% n=120
Late May
16th–end		 98% n=128
Full month average 89% n=248
11.0 h median sunshine per day 76% of days exceed 8 h sunshine 48% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 26%. Sunshine-based “warm & sunny”: 89%. The 63-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

San Antonio is mostly overcast in May historically: only 26% of days are clear across 8 years (n=248), avg high 88°F. If you want sun in San Antonio, 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 San Antonio.

Every month in San Antonio

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

Historical clear-sky % for San Antonio, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 10% n=248 All destinations →
February 19% n=226 All destinations →
March 33% n=248 All destinations →
April 36% n=240 All destinations →
May ← this page 26% n=248 All destinations →
June 31% n=240 All destinations →
July 44% n=248 All destinations →
August 45% n=248 All destinations →
September 36% n=240 All destinations →
October 49% n=248 All destinations →
November 33% n=240 All destinations →
December 17% 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.