Brewster, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 39.7 °F (low) to 62.4 °F (high). Annual precipitation averages 10.6 Inches. Brewster 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 23.3 °F | 34.2 °F | 1.59 in. |
| February | 25.6 °F | 40.9 °F | 1.06 in. |
| March | 32.1 °F | 53.8 °F | 0.97 in. |
| April | 38.6 °F | 64.2 °F | 0.6 in. |
| May | 46.1 °F | 73.9 °F | 0.79 in. |
| June | 52.1 °F | 80.3 °F | 0.87 in. |
| July | 58.2 °F | 89.9 °F | 0.42 in. |
| August | 57.2 °F | 88.8 °F | 0.26 in. |
| September | 49.1 °F | 79.2 °F | 0.32 in. |
| October | 39.0 °F | 62.7 °F | 0.89 in. |
| November | 30.7 °F | 45.7 °F | 1.16 in. |
| December | 24.3 °F | 34.7 °F | 1.69 in. |
| Annual | 39.7 °F | 62.4 °F | 10.62 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| 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 6b : -5°F to 0°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |