South Ashburnham, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.1 °C (low) to 13.5 °C (high). Annual precipitation averages 1229.9 Millimeters. South 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.8 °C | -0.6 °C | 91.19 mm |
| February | -10.1 °C | 1.2 °C | 82.8 mm |
| March | -5.8 °C | 5.4 °C | 108.2 mm |
| April | 0.5 °C | 12.8 °C | 100.33 mm |
| May | 6.6 °C | 19.1 °C | 96.77 mm |
| June | 11.6 °C | 23.8 °C | 108.46 mm |
| July | 14.7 °C | 26.7 °C | 103.38 mm |
| August | 13.7 °C | 25.9 °C | 104.14 mm |
| September | 9.6 °C | 21.9 °C | 104.39 mm |
| October | 3.3 °C | 14.7 °C | 125.48 mm |
| November | -1.8 °C | 8.3 °C | 95.5 mm |
| December | -6.9 °C | 2.4 °C | 109.22 mm |
| Annual | 2.1 °C | 13.5 °C | 1229.86 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |