Ahtanum, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 37.9 °F (low) to 62.8 °F (high). Annual precipitation averages 9.3 Inches. Ahtanum is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 24.2 °F | 38.3 °F | 1.52 in. |
| February | 26.6 °F | 45.8 °F | 0.96 in. |
| March | 31.1 °F | 54.6 °F | 0.77 in. |
| April | 36.0 °F | 62.6 °F | 0.67 in. |
| May | 43.8 °F | 72.0 °F | 0.85 in. |
| June | 49.5 °F | 78.5 °F | 0.52 in. |
| July | 55.1 °F | 87.6 °F | 0.24 in. |
| August | 54.0 °F | 86.9 °F | 0.19 in. |
| September | 46.1 °F | 78.1 °F | 0.3 in. |
| October | 36.6 °F | 63.6 °F | 0.73 in. |
| November | 28.6 °F | 48.2 °F | 1.03 in. |
| December | 23.3 °F | 37.4 °F | 1.48 in. |
| Annual | 37.9 °F | 62.8 °F | 9.26 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 7a : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |