Coulee Dam, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 40.6 °F (low) to 62.6 °F (high). Annual precipitation averages 9.5 Inches. Coulee Dam is located in USDA Plant Hardiness Zone 7b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 25.5 °F | 35.6 °F | 1.1 in. |
| February | 27.2 °F | 42.0 °F | 0.71 in. |
| March | 32.1 °F | 53.0 °F | 0.9 in. |
| April | 37.8 °F | 62.9 °F | 0.85 in. |
| May | 45.5 °F | 72.8 °F | 1.02 in. |
| June | 52.1 °F | 79.7 °F | 0.91 in. |
| July | 58.8 °F | 89.9 °F | 0.46 in. |
| August | 58.4 °F | 89.5 °F | 0.29 in. |
| September | 50.3 °F | 79.5 °F | 0.27 in. |
| October | 40.7 °F | 63.4 °F | 0.71 in. |
| November | 32.6 °F | 46.4 °F | 1.02 in. |
| December | 26.6 °F | 36.2 °F | 1.24 in. |
| Annual | 40.6 °F | 62.6 °F | 9.48 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 7b : 5°F to 10°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 |