Napa, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 46.3 °F (low) to 70.6 °F (high). Annual precipitation averages 26.1 Inches. 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 | 38.7 °F | 57.0 °F | 5.21 in. |
| February | 40.6 °F | 60.9 °F | 5.03 in. |
| March | 42.6 °F | 64.9 °F | 3.54 in. |
| April | 44.5 °F | 68.8 °F | 1.77 in. |
| May | 48.2 °F | 73.4 °F | 0.95 in. |
| June | 51.9 °F | 78.9 °F | 0.24 in. |
| July | 54.0 °F | 81.1 °F | 0.0 in. |
| August | 54.1 °F | 81.5 °F | 0.03 in. |
| September | 51.9 °F | 81.7 °F | 0.1 in. |
| October | 48.0 °F | 76.1 °F | 1.21 in. |
| November | 42.2 °F | 65.2 °F | 2.65 in. |
| December | 38.6 °F | 57.1 °F | 5.37 in. |
| Annual | 46.3 °F | 70.6 °F | 26.1 in. |
| 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 : 25°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 9b : 25°F to 20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |