Climate averages 1991–2020
Napa weather
in December.
A cool, wet month: the coolest and the 10th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
December is a cool month in Napa: daytime highs average 14.2°C and nights cool to about 5.6°C. By daytime temperature it is the coolest month of the year.
Expect about 110 mm of rain on roughly 9 days, which makes December a wet month (the 10th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 9 h 33 min on an average December day.
The nearest other city in this atlas is Vallejo (22 km away). In December its highs average 13.9°C, about as warm as Napa, with 95 mm of rain.
Among the 498 cities listed in the United States, Napa ranks joint 155th of 498 for the warmest December highs and joint 430th of 498 for the driest December (rainfall, lowest first). The mean December high of those 498 cities is 10.5°C; Napa is 3.6°C warmer than that mean.
From December to January, average highs rise by 0.2°C to 14.4°C, and monthly rainfall rises from 110 mm to 116 mm.
The annual picture
December in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Napa climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 14.4°C5.3°C | 5.3°C | 116 | 9.4 | 9.810 h |
| February | 15.9°C6.3°C | 6.3°C | 117 | 8.7 | 10.711 h |
| March | 18.0°C7.5°C | 7.5°C | 86 | 8.4 | 11.912 h |
| April | 20.7°C9.0°C | 9.0°C | 38 | 4.9 | 13.213 h |
| May | 24.6°C11.5°C | 11.5°C | 20 | 3.2 | 14.214 h |
| June | 28.9°C13.9°C | 13.9°C | 4.7 | 0.9 | 14.815 h |
| July | 30.7°C14.7°C | 14.7°C | 0.4 | 0.1 | 14.515 h |
| August | 30.6°C14.9°C | 14.9°C | 0.7 | 0.2 | 13.714 h |
| September | 29.5°C14.6°C | 14.6°C | 2.0 | 0.4 | 12.512 h |
| October | 25.1°C12.6°C | 12.6°C | 26 | 2.9 | 11.211 h |
| November | 18.3°C8.4°C | 8.4°C | 56 | 5.9 | 10.110 h |
| December, selected | 14.2°C5.6°C | 5.6°C | 110 | 9.4 | 9.610 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
December in nearby cities
- Vallejo in DecemberUnited States · 22 kmHigh 13.9°C · Low 5.5°C · 95 mm rain
- Fairfield in DecemberUnited States · 22 kmHigh 13.6°C · Low 5.8°C · 101 mm rain
- Vacaville in DecemberUnited States · 27 kmHigh 13.8°C · Low 5.8°C · 101 mm rain
- Santa Rosa, United States in DecemberUnited States · 41 kmHigh 14.0°C · Low 4.2°C · 150 mm rain
- Concord (California), United States in DecemberUnited States · 42 kmHigh 13.8°C · Low 6.0°C · 84 mm rain
- Berkeley in DecemberUnited States · 47 kmHigh 13.6°C · Low 5.7°C · 87 mm rain
- Antioch in DecemberUnited States · 53 kmHigh 13.7°C · Low 6.3°C · 87 mm rain
- Oakland in DecemberUnited States · 55 kmHigh 13.8°C · Low 6.0°C · 87 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Napa) is explained once on the Napa year overview and on the Sources, method and limits page.