Climate averages 1991–2020
Napa weather
in August.
A hot, very dry month: the 2nd warmest and the 2nd driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
August is a hot month in Napa: daytime highs average 30.6°C and nights cool to about 14.9°C. By daytime temperature it is the 2nd warmest of the 12 months.
Rain is very rare: less than 1 mm falls in a typical August (the 2nd driest of the 12 months). Daylight, from sunrise to sunset, lasts about 13 h 39 min on an average August day.
The nearest other city in this atlas is Vallejo (22 km away). In August its highs average 28.6°C, 2.0°C cooler than Napa, with almost no rain (under 1 mm).
Among the 498 cities listed in the United States, Napa ranks joint 190th of 498 for the warmest August highs and joint 29th of 498 for the driest August (rainfall, lowest first). The mean August high of those 498 cities is 29.9°C; Napa is 0.7°C warmer than that mean.
From August to September, average highs fall by 1.1°C to 29.5°C, and monthly rainfall rises from under 1 mm to 2.0 mm.
The annual picture
August 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, selected | 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 | 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
August in nearby cities
- Vallejo in AugustUnited States · 22 kmHigh 28.6°C · Low 13.8°C · 0.9 mm rain
- Fairfield in AugustUnited States · 22 kmHigh 29.8°C · Low 14.6°C · 1.0 mm rain
- Vacaville in AugustUnited States · 27 kmHigh 32.0°C · Low 15.7°C · 1.0 mm rain
- Santa Rosa, United States in AugustUnited States · 41 kmHigh 29.5°C · Low 14.3°C · 1.1 mm rain
- Concord (California), United States in AugustUnited States · 42 kmHigh 28.8°C · Low 14.5°C · 1.5 mm rain
- Berkeley in AugustUnited States · 47 kmHigh 26.2°C · Low 13.6°C · 0.9 mm rain
- Antioch in AugustUnited States · 53 kmHigh 30.0°C · Low 15.4°C · 1.5 mm rain
- Oakland in AugustUnited States · 55 kmHigh 26.3°C · Low 14.2°C · 0.9 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.