Stevenson, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 7 °C (low) to 16.6 °C (high). Annual precipitation averages 1983 Millimeters. 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 | 1.6 °C | 6.4 °C | 294.13 mm |
| February | 2.1 °C | 9.1 °C | 209.04 mm |
| March | 3.4 °C | 12.4 °C | 232.66 mm |
| April | 5.6 °C | 15.7 °C | 161.04 mm |
| May | 8.6 °C | 19.8 °C | 95.25 mm |
| June | 11.3 °C | 22.5 °C | 62.23 mm |
| July | 13.7 °C | 26.9 °C | 15.24 mm |
| August | 13.7 °C | 27.5 °C | 17.02 mm |
| September | 10.8 °C | 24.3 °C | 60.2 mm |
| October | 7.5 °C | 17.7 °C | 184.66 mm |
| November | 4.2 °C | 10.6 °C | 304.04 mm |
| December | 1.7 °C | 6.4 °C | 347.47 mm |
| Annual | 7 °C | 16.6 °C | 1982.98 mm |
| 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 : -6.7°C to -3.9°C |
| Plant Hardiness Zone - 2012 | Zone 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |