Millbury, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.5 °C (low) to 15 °C (high). Annual precipitation averages 1256.8 Millimeters. Millbury is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9 °C | 1.5 °C | 96.77 mm |
| February | -8.4 °C | 2.9 °C | 84.84 mm |
| March | -3.9 °C | 7.2 °C | 116.59 mm |
| April | 1.8 °C | 14.3 °C | 111.25 mm |
| May | 7.8 °C | 20.2 °C | 91.19 mm |
| June | 12.9 °C | 24.7 °C | 107.19 mm |
| July | 16.1 °C | 27.7 °C | 98.04 mm |
| August | 15.2 °C | 26.8 °C | 105.66 mm |
| September | 10.8 °C | 23.1 °C | 103.12 mm |
| October | 4.6 °C | 16.4 °C | 126.75 mm |
| November | -0.8 °C | 10.3 °C | 97.28 mm |
| December | -5.4 °C | 4.6 °C | 118.11 mm |
| Annual | 3.5 °C | 15 °C | 1256.79 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 125-150 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 | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |