Rio Oso, California has a Hot-Summer Mediterranean Climate climate (Köppen classification: Csa). Average annual temperatures range from 9.1 °C (low) to 23.6 °C (high). Annual precipitation averages 496.3 Millimeters. Rio Oso 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. 1 - Dec. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 3.6 °C | 13 °C | 100.33 mm |
| February | 4.8 °C | 16 °C | 87.63 mm |
| March | 6.3 °C | 18.8 °C | 73.41 mm |
| April | 7.8 °C | 21.9 °C | 35.81 mm |
| May | 11.1 °C | 26.5 °C | 21.59 mm |
| June | 14 °C | 30.9 °C | 4.57 mm |
| July | 15.7 °C | 34 °C | 0 mm |
| August | 15 °C | 33.5 °C | 1.27 mm |
| September | 13.3 °C | 31.1 °C | 3.3 mm |
| October | 9.6 °C | 25.7 °C | 21.59 mm |
| November | 5.3 °C | 18.1 °C | 52.07 mm |
| December | 3.2 °C | 13.1 °C | 94.74 mm |
| Annual | 9.1 °C | 23.6 °C | 496.31 mm |
| Average First Frost Date | Dec. 1 - Dec. 10 |
| 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 | Abnormally Dry |
| Köppen Climate Classification | Csa - Hot-Summer Mediterranean Climate |