Ashburnham, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 35.5 °F (low) to 55.4 °F (high). Annual precipitation averages 48.9 Inches. Ashburnham is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 12.4 °F | 30.3 °F | 3.51 in. |
| February | 13.8 °F | 33.5 °F | 3.24 in. |
| March | 21.3 °F | 40.9 °F | 4.3 in. |
| April | 32.7 °F | 54.2 °F | 4.05 in. |
| May | 43.1 °F | 65.6 °F | 3.98 in. |
| June | 52.5 °F | 74.0 °F | 4.26 in. |
| July | 58.1 °F | 79.1 °F | 4.0 in. |
| August | 56.2 °F | 77.6 °F | 4.11 in. |
| September | 49.1 °F | 70.4 °F | 4.15 in. |
| October | 38.2 °F | 57.6 °F | 5.04 in. |
| November | 28.8 °F | 46.2 °F | 3.79 in. |
| December | 19.5 °F | 35.7 °F | 4.47 in. |
| Annual | 35.5 °F | 55.4 °F | 48.9 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |