Bethel Island, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 9.5 °C (low) to 22.6 °C (high). Annual precipitation averages 370.6 Millimeters. Bethel Island 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. 11 - Dec. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 4 °C | 13.2 °C | 76.2 mm |
| February | 5.4 °C | 15.9 °C | 71.12 mm |
| March | 7.1 °C | 18.8 °C | 49.53 mm |
| April | 8.8 °C | 21.3 °C | 29.21 mm |
| May | 11.3 °C | 24.9 °C | 13.72 mm |
| June | 13.6 °C | 28.8 °C | 4.57 mm |
| July | 14.7 °C | 31.3 °C | 0 mm |
| August | 14.7 °C | 30.8 °C | 0.51 mm |
| September | 13.7 °C | 29.5 °C | 1.78 mm |
| October | 10.5 °C | 25.1 °C | 18.03 mm |
| November | 6.3 °C | 18.3 °C | 36.83 mm |
| December | 3.8 °C | 13.3 °C | 69.09 mm |
| Annual | 9.5 °C | 22.6 °C | 370.59 mm |
| Average First Frost Date | Dec. 11 - Dec. 20 |
| 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 |