Mattawa, Washington has a Cold Desert Climate climate (Köppen classification: BWk). Average annual temperatures range from 5.4 °C (low) to 18 °C (high). Annual precipitation averages 194.8 Millimeters. Mattawa is located in USDA Plant Hardiness Zone 7b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -3.2 °C | 4.1 °C | 27.18 mm |
| February | -1.6 °C | 8.1 °C | 17.27 mm |
| March | 1.2 °C | 13.4 °C | 18.03 mm |
| April | 4.3 °C | 18.1 °C | 14.73 mm |
| May | 8.7 °C | 23.3 °C | 14.73 mm |
| June | 12.2 °C | 27.1 °C | 16.26 mm |
| July | 15.7 °C | 32.3 °C | 6.86 mm |
| August | 15.1 °C | 31.7 °C | 3.3 mm |
| September | 10.4 °C | 26.6 °C | 4.57 mm |
| October | 4.7 °C | 18.2 °C | 16.76 mm |
| November | -0.1 °C | 9.4 °C | 23.37 mm |
| December | -3.1 °C | 3.9 °C | 31.75 mm |
| Annual | 5.4 °C | 18 °C | 194.81 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7b : -15°C to -12.2°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | BWk - Cold Desert Climate |