Westfield, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 35.1 °F (low) to 57.6 °F (high). Annual precipitation averages 37.8 Inches. 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 | 13.9 °F | 32.3 °F | 2.35 in. |
| February | 14.7 °F | 34.8 °F | 1.88 in. |
| March | 21.6 °F | 43.2 °F | 2.59 in. |
| April | 32.0 °F | 56.6 °F | 3.09 in. |
| May | 43.0 °F | 68.9 °F | 3.53 in. |
| June | 51.8 °F | 77.1 °F | 3.92 in. |
| July | 56.0 °F | 81.1 °F | 3.81 in. |
| August | 54.6 °F | 79.9 °F | 3.62 in. |
| September | 47.6 °F | 73.0 °F | 3.92 in. |
| October | 37.2 °F | 60.5 °F | 3.66 in. |
| November | 28.3 °F | 47.4 °F | 2.86 in. |
| December | 20.7 °F | 36.8 °F | 2.55 in. |
| Annual | 35.1 °F | 57.6 °F | 37.78 in. |
| 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 : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |