Washington, New Hampshire has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.2 °C (low) to 12.3 °C (high). Annual precipitation averages 1348 Millimeters. Washington is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.1 °C | -2.5 °C | 97.54 mm |
| February | -9.5 °C | -0.8 °C | 87.88 mm |
| March | -5.1 °C | 3.8 °C | 104.39 mm |
| April | 1.4 °C | 11.8 °C | 105.41 mm |
| May | 7.6 °C | 18.8 °C | 105.16 mm |
| June | 13.4 °C | 23.2 °C | 122.68 mm |
| July | 16.4 °C | 25.6 °C | 131.57 mm |
| August | 14.9 °C | 24.8 °C | 113.28 mm |
| September | 10.9 °C | 20.9 °C | 110.24 mm |
| October | 5.3 °C | 13.7 °C | 146.05 mm |
| November | -0.8 °C | 7.1 °C | 104.14 mm |
| December | -5.5 °C | 0.7 °C | 119.63 mm |
| Annual | 3.2 °C | 12.3 °C | 1347.97 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |