Oso, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 41.4 °F (low) to 59.9 °F (high). Annual precipitation averages 51.5 Inches. Oso is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 33.1 °F | 45.1 °F | 6.47 in. |
| February | 33.1 °F | 48.3 °F | 4.65 in. |
| March | 35.5 °F | 52.6 °F | 5.43 in. |
| April | 39.4 °F | 58.6 °F | 4.42 in. |
| May | 44.6 °F | 65.6 °F | 3.01 in. |
| June | 49.0 °F | 69.5 °F | 2.63 in. |
| July | 51.9 °F | 76.3 °F | 1.16 in. |
| August | 51.9 °F | 77.4 °F | 1.22 in. |
| September | 47.9 °F | 71.3 °F | 2.54 in. |
| October | 41.6 °F | 59.8 °F | 5.34 in. |
| November | 36.5 °F | 50.0 °F | 7.65 in. |
| December | 32.8 °F | 44.1 °F | 6.99 in. |
| Annual | 41.4 °F | 59.9 °F | 51.51 in. |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 8b : 15°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 8b : 15°F to 20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |