Stevenson, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 44.6 °F (low) to 61.9 °F (high). Annual precipitation averages 78.1 Inches. Stevenson is located in USDA Plant Hardiness Zone 9a. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Nov. 11 - Nov. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 34.9 °F | 43.6 °F | 11.58 in. |
| February | 35.7 °F | 48.3 °F | 8.23 in. |
| March | 38.2 °F | 54.4 °F | 9.16 in. |
| April | 42.0 °F | 60.2 °F | 6.34 in. |
| May | 47.5 °F | 67.7 °F | 3.75 in. |
| June | 52.3 °F | 72.5 °F | 2.45 in. |
| July | 56.7 °F | 80.4 °F | 0.6 in. |
| August | 56.6 °F | 81.5 °F | 0.67 in. |
| September | 51.5 °F | 75.7 °F | 2.37 in. |
| October | 45.5 °F | 63.8 °F | 7.27 in. |
| November | 39.6 °F | 51.1 °F | 11.97 in. |
| December | 35.1 °F | 43.6 °F | 13.68 in. |
| Annual | 44.6 °F | 61.9 °F | 78.07 in. |
| Average First Frost Date | Nov. 11 - Nov. 20 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 9a : 20°F to 25°F |
| Plant Hardiness Zone - 2012 | Zone 8b : 15°F to 20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |