Westerlo, New York has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.3 °C (low) to 13.5 °C (high). Annual precipitation averages 1130.3 Millimeters. Westerlo is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.6 °C | -0.6 °C | 75.18 mm |
| February | -10.9 °C | 0.8 °C | 62.74 mm |
| March | -6.6 °C | 5.3 °C | 84.07 mm |
| April | -0.2 °C | 13 °C | 91.95 mm |
| May | 6.3 °C | 19.8 °C | 88.39 mm |
| June | 11.2 °C | 24.1 °C | 118.36 mm |
| July | 13.7 °C | 26.6 °C | 104.14 mm |
| August | 12.7 °C | 25.6 °C | 109.22 mm |
| September | 8.6 °C | 21.8 °C | 102.87 mm |
| October | 2.7 °C | 14.9 °C | 121.41 mm |
| November | -2.3 °C | 8.4 °C | 81.03 mm |
| December | -7.6 °C | 2.2 °C | 90.93 mm |
| Annual | 1.3 °C | 13.5 °C | 1130.29 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| 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 | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |