Brewster, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 4.3 °C (low) to 16.9 °C (high). Annual precipitation averages 269.8 Millimeters. 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 | -4.8 °C | 1.2 °C | 40.39 mm |
| February | -3.6 °C | 4.9 °C | 26.92 mm |
| March | 0.1 °C | 12.1 °C | 24.64 mm |
| April | 3.7 °C | 17.9 °C | 15.24 mm |
| May | 7.8 °C | 23.3 °C | 20.07 mm |
| June | 11.2 °C | 26.8 °C | 22.1 mm |
| July | 14.6 °C | 32.2 °C | 10.67 mm |
| August | 14 °C | 31.6 °C | 6.6 mm |
| September | 9.5 °C | 26.2 °C | 8.13 mm |
| October | 3.9 °C | 17.1 °C | 22.61 mm |
| November | -0.7 °C | 7.6 °C | 29.46 mm |
| December | -4.3 °C | 1.5 °C | 42.93 mm |
| Annual | 4.3 °C | 16.9 °C | 269.76 mm |
| 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 : -17.8°C to -15°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 |