Fitchburg, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.1 °C (low) to 14.8 °C (high). Annual precipitation averages 1255.5 Millimeters. Fitchburg is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9.8 °C | 0.8 °C | 96.01 mm |
| February | -8.9 °C | 2.3 °C | 86.87 mm |
| March | -4.5 °C | 6.7 °C | 112.78 mm |
| April | 1.6 °C | 14.1 °C | 105.66 mm |
| May | 7.7 °C | 20.3 °C | 97.79 mm |
| June | 12.9 °C | 25.2 °C | 109.47 mm |
| July | 16 °C | 28.2 °C | 100.33 mm |
| August | 14.9 °C | 27.3 °C | 95.5 mm |
| September | 10.5 °C | 23.3 °C | 106.17 mm |
| October | 3.9 °C | 16.3 °C | 130.05 mm |
| November | -1.2 °C | 9.7 °C | 100.33 mm |
| December | -6.2 °C | 3.8 °C | 114.55 mm |
| Annual | 3.1 °C | 14.8 °C | 1255.51 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 |