Napa, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 7.9 °C (low) to 21.4 °C (high). Annual precipitation averages 662.9 Millimeters. Napa is located in USDA Plant Hardiness Zone 9b. The growing season typically runs from the last frost around Feb. 1 - Feb. 10 through the first frost around Dec. 1 - Dec. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 3.7 °C | 13.9 °C | 132.33 mm |
| February | 4.8 °C | 16.1 °C | 127.76 mm |
| March | 5.9 °C | 18.3 °C | 89.92 mm |
| April | 6.9 °C | 20.4 °C | 44.96 mm |
| May | 9 °C | 23 °C | 24.13 mm |
| June | 11.1 °C | 26.1 °C | 6.1 mm |
| July | 12.2 °C | 27.3 °C | 0 mm |
| August | 12.3 °C | 27.5 °C | 0.76 mm |
| September | 11.1 °C | 27.6 °C | 2.54 mm |
| October | 8.9 °C | 24.5 °C | 30.73 mm |
| November | 5.7 °C | 18.4 °C | 67.31 mm |
| December | 3.7 °C | 13.9 °C | 136.4 mm |
| Annual | 7.9 °C | 21.4 °C | 662.94 mm |
| Average First Frost Date | Dec. 1 - Dec. 10 |
| Average Last Frost Date | Feb. 1 - Feb. 10 |
| Average Days With Frost | 10-20 Days |
| Plant Hardiness Zone | Zone 9b : -3.9°C to -1.1°C |
| Plant Hardiness Zone - 2012 | Zone 9b : -3.9°C to -1.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |