Westby, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.5 °C (low) to 12.3 °C (high). Annual precipitation averages 934.7 Millimeters. Westby is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -12.9 °C | -4.7 °C | 27.94 mm |
| February | -10.9 °C | -2 °C | 25.4 mm |
| March | -4.8 °C | 4.9 °C | 44.96 mm |
| April | 1.9 °C | 12.9 °C | 97.03 mm |
| May | 8.5 °C | 19.6 °C | 119.63 mm |
| June | 14.1 °C | 24.6 °C | 137.67 mm |
| July | 16.3 °C | 26.8 °C | 114.55 mm |
| August | 15.2 °C | 25.7 °C | 116.59 mm |
| September | 10.6 °C | 21.6 °C | 97.54 mm |
| October | 4.1 °C | 14.3 °C | 68.83 mm |
| November | -2.9 °C | 5.5 °C | 47.24 mm |
| December | -9.1 °C | -1.6 °C | 37.34 mm |
| Annual | 2.5 °C | 12.3 °C | 934.72 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |