Ahtanum, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 3.3 °C (low) to 17.1 °C (high). Annual precipitation averages 235.2 Millimeters. 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 | -4.3 °C | 3.5 °C | 38.61 mm |
| February | -3 °C | 7.7 °C | 24.38 mm |
| March | -0.5 °C | 12.6 °C | 19.56 mm |
| April | 2.2 °C | 17 °C | 17.02 mm |
| May | 6.6 °C | 22.2 °C | 21.59 mm |
| June | 9.7 °C | 25.8 °C | 13.21 mm |
| July | 12.8 °C | 30.9 °C | 6.1 mm |
| August | 12.2 °C | 30.5 °C | 4.83 mm |
| September | 7.8 °C | 25.6 °C | 7.62 mm |
| October | 2.6 °C | 17.6 °C | 18.54 mm |
| November | -1.9 °C | 9 °C | 26.16 mm |
| December | -4.8 °C | 3 °C | 37.59 mm |
| Annual | 3.3 °C | 17.1 °C | 235.21 mm |
| 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 : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |