Grand Coulee, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 39.6 °F (low) to 61.5 °F (high). Annual precipitation averages 10.8 Inches. Grand Coulee is located in USDA Plant Hardiness Zone 7a. 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 | 24.4 °F | 34.6 °F | 1.22 in. |
| February | 26.2 °F | 40.9 °F | 0.87 in. |
| March | 31.5 °F | 51.8 °F | 1.02 in. |
| April | 37.0 °F | 61.7 °F | 0.92 in. |
| May | 44.6 °F | 71.6 °F | 1.1 in. |
| June | 50.9 °F | 78.5 °F | 1.04 in. |
| July | 57.6 °F | 88.7 °F | 0.49 in. |
| August | 57.3 °F | 88.3 °F | 0.32 in. |
| September | 49.4 °F | 78.4 °F | 0.37 in. |
| October | 39.6 °F | 62.3 °F | 0.83 in. |
| November | 31.4 °F | 45.5 °F | 1.14 in. |
| December | 25.2 °F | 35.2 °F | 1.44 in. |
| Annual | 39.6 °F | 61.5 °F | 10.76 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 7a : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 7a : 0°F to 5°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |