Rio Dell, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 7.5 °C (low) to 17 °C (high). Annual precipitation averages 1152.1 Millimeters. Rio Dell is located in USDA Plant Hardiness Zone 9b.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 4.8 °C | 12.9 °C | 214.38 mm |
| February | 5 °C | 13.6 °C | 182.12 mm |
| March | 5.4 °C | 14.3 °C | 167.89 mm |
| April | 6.3 °C | 15.4 °C | 96.01 mm |
| May | 8.2 °C | 18.4 °C | 45.97 mm |
| June | 9.7 °C | 18.6 °C | 16.76 mm |
| July | 11.2 °C | 19.9 °C | 4.06 mm |
| August | 11.3 °C | 21.1 °C | 2.54 mm |
| September | 9.9 °C | 21.4 °C | 11.68 mm |
| October | 7.9 °C | 20.9 °C | 57.91 mm |
| November | 6.1 °C | 15.1 °C | 124.46 mm |
| December | 4.5 °C | 12.3 °C | 228.35 mm |
| Annual | 7.5 °C | 17 °C | 1152.13 mm |
| Average First Frost Date | Frost Rare |
| Average Last Frost Date | |
| Average Days With Frost | Frost Rare |
| 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 | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |