Bethel Island, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 49.1 °F (low) to 72.7 °F (high). Annual precipitation averages 14.6 Inches. 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 | 39.2 °F | 55.7 °F | 3.0 in. |
| February | 41.7 °F | 60.7 °F | 2.8 in. |
| March | 44.8 °F | 65.8 °F | 1.95 in. |
| April | 47.8 °F | 70.3 °F | 1.15 in. |
| May | 52.3 °F | 76.9 °F | 0.54 in. |
| June | 56.4 °F | 83.9 °F | 0.18 in. |
| July | 58.5 °F | 88.3 °F | 0.0 in. |
| August | 58.5 °F | 87.5 °F | 0.02 in. |
| September | 56.6 °F | 85.1 °F | 0.07 in. |
| October | 50.9 °F | 77.1 °F | 0.71 in. |
| November | 43.3 °F | 65.0 °F | 1.45 in. |
| December | 38.9 °F | 56.0 °F | 2.72 in. |
| Annual | 49.1 °F | 72.7 °F | 14.59 in. |
| 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 : 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 |