Fairfield, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 2.1 °C (low) to 14.4 °C (high). Annual precipitation averages 559.3 Millimeters. Fairfield is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.2 °C | 2.3 °C | 69.6 mm |
| February | -3.7 °C | 4.4 °C | 50.29 mm |
| March | -1.5 °C | 8.8 °C | 60.2 mm |
| April | 1.1 °C | 13.3 °C | 46.48 mm |
| May | 4.7 °C | 18.4 °C | 52.58 mm |
| June | 7.7 °C | 21.9 °C | 42.67 mm |
| July | 10.1 °C | 28.3 °C | 15.49 mm |
| August | 10.1 °C | 28.7 °C | 13.72 mm |
| September | 6 °C | 23.3 °C | 18.8 mm |
| October | 1.6 °C | 14.9 °C | 45.72 mm |
| November | -1.6 °C | 6.4 °C | 69.09 mm |
| December | -4.6 °C | 1.6 °C | 74.68 mm |
| Annual | 2.1 °C | 14.4 °C | 559.32 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°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 |