Monte Rio, California has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.7 °C (low) to 20.9 °C (high). Annual precipitation averages 1246.9 Millimeters. Monte Rio is located in USDA Plant Hardiness Zone 9b. The growing season typically runs from the last frost around Feb. 11 - Feb. 20 through the first frost around Dec. 11 - Dec. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 3.4 °C | 14.1 °C | 238.51 mm |
| February | 4.1 °C | 15.8 °C | 242.06 mm |
| March | 5 °C | 17.4 °C | 170.18 mm |
| April | 5.8 °C | 19.7 °C | 81.28 mm |
| May | 7.6 °C | 22.5 °C | 46.99 mm |
| June | 9.3 °C | 25.4 °C | 7.37 mm |
| July | 10.4 °C | 26.2 °C | 1.27 mm |
| August | 10.6 °C | 26.8 °C | 2.54 mm |
| September | 9.3 °C | 26.2 °C | 4.32 mm |
| October | 7.4 °C | 23.7 °C | 55.88 mm |
| November | 4.9 °C | 18.3 °C | 126.49 mm |
| December | 3.1 °C | 14.2 °C | 270 mm |
| Annual | 6.7 °C | 20.9 °C | 1246.89 mm |
| Average First Frost Date | Dec. 11 - Dec. 20 |
| Average Last Frost Date | Feb. 11 - Feb. 20 |
| Average Days With Frost | 20-30 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 |