| 2023 Hardiness Zone: | Zone 9a: 20°F to 25°F Zone 9b: 25°F to 30°F |
| 2012 Hardiness Zone: | Zone 9a: 20°F to 25°F Zone 9b: 25°F to 30°F Zone 10a: 30°F to 35°F |
| 1990 Hardiness Zone: | Zone 9b: 25F to 30F |
| Average First Frost Date: | Nov. 21 - Nov. 30 |
| Average Last Frost Date: | Mar. 21 - Mar. 31 |
| Koppen-Geiger Climate Zone: | Csb - Warm-Summer Mediterranean Climate |
| Ecoregion: | |
| Heat Zone Days: | 61 - 90 days Over 86°F |
Annual Climate Data for ZIP Code 94574 - Saint Helena, CA | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 38 | 40 | 41 | 43 | 47 | 52 | 54 | 54 | 52 | 48 | 42 | 37 | 46 |
| Avg Max Temp (°F) | 56 | 60 | 63 | 70 | 77 | 84 | 88 | 87 | 84 | 76 | 63 | 56 | 72 |
| Avg Precip (In.) | 7.14 | 6.79 | 5.15 | 1.72 | .69 | .17 | .04 | .08 | .41 | 1.81 | 4.62 | 5.02 | 33.65 |