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SunnyDays

ERA5 almanac — 8 years of real data

Wine Country Sonoma in October

Wine Country 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 Wine Country 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 Wine Country 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

Sunshine & warmth in October

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 Wine Country Sonoma in October. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early October
1st–15th		 82% n=120
Late October
16th–end		 62% n=128
Full month average 72% n=248
10.5 h median sunshine per day 87% of days exceed 8 h sunshine 12% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 68%. Sunshine-based “warm & sunny”: 72%.

Bottom line

Wine Country 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 Wine Country Sonoma

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

Historical clear-sky % for Wine Country 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 →

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.