Westfield, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.4 °C (low) to 15.6 °C (high). Annual precipitation averages 1259.9 Millimeters. Westfield is located in USDA Plant Hardiness Zone 6b. 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 | -8.3 °C | 1.6 °C | 86.87 mm |
| February | -7.6 °C | 3.1 °C | 77.47 mm |
| March | -2.9 °C | 7.7 °C | 102.62 mm |
| April | 3.2 °C | 15.2 °C | 106.93 mm |
| May | 9 °C | 21.4 °C | 92.46 mm |
| June | 14.1 °C | 26 °C | 115.32 mm |
| July | 17.1 °C | 28.9 °C | 105.41 mm |
| August | 16.1 °C | 27.9 °C | 109.22 mm |
| September | 11.8 °C | 23.9 °C | 117.35 mm |
| October | 5.4 °C | 17 °C | 135.89 mm |
| November | 0.1 °C | 10.5 °C | 93.98 mm |
| December | -4.7 °C | 4.5 °C | 116.33 mm |
| Annual | 4.4 °C | 15.6 °C | 1259.85 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 6b : -20.6°C to -17.8°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 |