Coulee Dam, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 4.8 °C (low) to 17 °C (high). Annual precipitation averages 240.8 Millimeters. 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 | -3.6 °C | 2 °C | 27.94 mm |
| February | -2.7 °C | 5.6 °C | 18.03 mm |
| March | 0.1 °C | 11.7 °C | 22.86 mm |
| April | 3.2 °C | 17.2 °C | 21.59 mm |
| May | 7.5 °C | 22.7 °C | 25.91 mm |
| June | 11.2 °C | 26.5 °C | 23.11 mm |
| July | 14.9 °C | 32.2 °C | 11.68 mm |
| August | 14.7 °C | 31.9 °C | 7.37 mm |
| September | 10.2 °C | 26.4 °C | 6.86 mm |
| October | 4.8 °C | 17.4 °C | 18.03 mm |
| November | 0.3 °C | 8 °C | 25.91 mm |
| December | -3 °C | 2.3 °C | 31.5 mm |
| Annual | 4.8 °C | 17 °C | 240.79 mm |
| 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 : -15°C to -12.2°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 |