Rio Oso, California has a Hot-Summer Mediterranean Climate climate (Köppen classification: Csa). Average annual temperatures range from 48.5 °F (low) to 74.4 °F (high). Annual precipitation averages 19.5 Inches. 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 | 38.5 °F | 55.4 °F | 3.95 in. |
| February | 40.7 °F | 60.8 °F | 3.45 in. |
| March | 43.4 °F | 65.9 °F | 2.89 in. |
| April | 46.0 °F | 71.5 °F | 1.41 in. |
| May | 51.9 °F | 79.7 °F | 0.85 in. |
| June | 57.2 °F | 87.6 °F | 0.18 in. |
| July | 60.2 °F | 93.2 °F | 0.0 in. |
| August | 59.0 °F | 92.3 °F | 0.05 in. |
| September | 55.9 °F | 87.9 °F | 0.13 in. |
| October | 49.2 °F | 78.2 °F | 0.85 in. |
| November | 41.6 °F | 64.6 °F | 2.05 in. |
| December | 37.8 °F | 55.6 °F | 3.73 in. |
| Annual | 48.5 °F | 74.4 °F | 19.54 in. |
| 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 : 25°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 9b : 25°F to 20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csa - Hot-Summer Mediterranean Climate |