Westfield, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.7 °C (low) to 14.3 °C (high). Annual precipitation averages 959.6 Millimeters. Westfield is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.1 °C | 0.2 °C | 59.69 mm |
| February | -9.6 °C | 1.6 °C | 47.75 mm |
| March | -5.8 °C | 6.2 °C | 65.79 mm |
| April | 0 °C | 13.7 °C | 78.49 mm |
| May | 6.1 °C | 20.5 °C | 89.66 mm |
| June | 11 °C | 25.1 °C | 99.57 mm |
| July | 13.3 °C | 27.3 °C | 96.77 mm |
| August | 12.6 °C | 26.6 °C | 91.95 mm |
| September | 8.7 °C | 22.8 °C | 99.57 mm |
| October | 2.9 °C | 15.8 °C | 92.96 mm |
| November | -2.1 °C | 8.6 °C | 72.64 mm |
| December | -6.3 °C | 2.7 °C | 64.77 mm |
| Annual | 1.7 °C | 14.3 °C | 959.61 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |