ERA5 almanac — 8 years of real data

Sonoma in October

Sonoma in October: rain frequency data not yet backfilled for this month, 78°F average high, 68% of days historically clear (n=248, ERA5 2018–2025).

Sonoma in October is a mixed month for sun: 68% of days historically clear (n=248, avg high 78°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 Sonoma 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 October

Clear-sky percentage for Sonoma in October, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period	% Clear days	Sample (n)	Avg high
Early October 1st–15th	78%	n=120	78°F
Late October 16th–end	58%	n=128	78°F
Full month average	68%	n=248	78°F

Bottom line

Sonoma clears solidly in October: 68% of days historically (n=248), avg high 78°F. The two halves differ materially (78% early, 58% late) — favour the early half of the month. Most trips here in October will find more sun than cloud.

Every month in Sonoma

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

Historical clear-sky % for Sonoma, all months, ERA5 2018–2025.
Month	% Clear	Sample (n)
January	1%	n=248	All destinations →
February	8%	n=226	All destinations →
March	8%	n=248	All destinations →
April	32%	n=240	All destinations →
May	61%	n=248	All destinations →
June	90%	n=240	All destinations →
July	96%	n=248	All destinations →
August	95%	n=248	All destinations →
September	86%	n=240	All destinations →
October ← this page	68%	n=248	All destinations →
November	16%	n=240	All destinations →
December	0%	n=248	All destinations →

Frequently asked

Is Sonoma good for sun in October?

Yes. Sonoma is historically strong for sun in October: 68% of days are clear on average (avg high 78°F, n=248 days, ERA5 2018–2025).

→ Sonoma live forecast — this week’s actual 7-day weather, not historical
→ Best destinations in October — all destinations ranked by October 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.