ERA5 almanac comparison — 8 years of real data
San Diego vs Wine Country Sonoma: weather in January
San Diego edges out Wine Country Sonoma for sun in January: 6% clear historically versus 1% (8-year ERA5 average, a 5-point gap). Wine Country Sonoma also sees measurably more rain than San Diego this month (34% vs 19% of days). Both are viable — San Diego is the safer bet.
What you are reading: 8-year historical averages, not a forecast.
Either destination can still surprise you this specific January. For this
week’s actual forecast, each destination links to its live page below.
San Diego
CA
- Clear days, January
- 6%
- Sample size
- n=248 days
- Avg high
- 64°F
- Early January (1st–15th)
- 2%
- Late January (16th–end)
- 9%
- Rain frequency
- 19% of days
Wine Country Sonoma
CA
- Clear days, January
- 1%
- Sample size
- n=248 days
- Avg high
- 58°F
- Early January (1st–15th)
- 0%
- Late January (16th–end)
- 2%
- Rain frequency
- 34% of days
Compare San Diego vs Wine Country Sonoma in another month
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.