Rio Dell, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 45.6 °F (low) to 62.6 °F (high). Annual precipitation averages 45.4 Inches. Rio Dell is located in USDA Plant Hardiness Zone 9b.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 40.7 °F | 55.2 °F | 8.44 in. |
| February | 41.0 °F | 56.4 °F | 7.17 in. |
| March | 41.7 °F | 57.7 °F | 6.61 in. |
| April | 43.3 °F | 59.7 °F | 3.78 in. |
| May | 46.8 °F | 65.1 °F | 1.81 in. |
| June | 49.5 °F | 65.4 °F | 0.66 in. |
| July | 52.2 °F | 67.9 °F | 0.16 in. |
| August | 52.4 °F | 70.0 °F | 0.1 in. |
| September | 49.9 °F | 70.6 °F | 0.46 in. |
| October | 46.3 °F | 69.6 °F | 2.28 in. |
| November | 43.0 °F | 59.2 °F | 4.9 in. |
| December | 40.1 °F | 54.2 °F | 8.99 in. |
| Annual | 45.6 °F | 62.6 °F | 45.36 in. |
| Average First Frost Date | Frost Rare |
| Average Last Frost Date | |
| Average Days With Frost | Frost Rare |
| Plant Hardiness Zone | Zone 9b : 25°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 9b : 25°F to 20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |