ERA5 almanac — 8 years of real data

San Francisco in August

San Francisco in August: rain frequency data not yet backfilled for this month, 68°F average high, 21% of days historically clear (n=248, ERA5 2018–2025).

San Francisco in August is historically a poor month for sun: only 21% of days clear across 8 years (n=248, avg high 68°F). October is the clearest month for San Francisco 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 Francisco 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 August

Clear-sky percentage for San Francisco in August, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period	% Clear days	Sample (n)	Avg high
Early August 1st–15th	15%	n=120	68°F
Late August 16th–end	27%	n=128	68°F
Full month average	21%	n=248	68°F

Bottom line

San Francisco is mostly overcast in August historically: only 21% of days are clear across 8 years (n=248), avg high 68°F. If you want sun in San Francisco, 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 Francisco.

Every month in San Francisco

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

Historical clear-sky % for San Francisco, all months, ERA5 2018–2025.
Month	% Clear	Sample (n)
January	0%	n=248	All destinations →
February	1%	n=226	All destinations →
March	3%	n=248	All destinations →
April	2%	n=240	All destinations →
May	7%	n=248	All destinations →
June	14%	n=240	All destinations →
July	8%	n=248	All destinations →
August ← this page	21%	n=248	All destinations →
September	16%	n=240	All destinations →
October	28%	n=248	All destinations →
November	6%	n=240	All destinations →
December	0%	n=248	All destinations →

Frequently asked

Is San Francisco good for sun in August?

Not usually. San Francisco is historically overcast in August: only 21% of days are clear (avg high 68°F, n=248 days, ERA5 2018–2025). October is historically far better for sun here.

→ San Francisco live forecast — this week’s actual 7-day weather, not historical
→ Best destinations in August — all destinations ranked by August clear-sky %
→ All destinations
→ Raw data (JSON) — buckets, n, source

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.