Birnamwood, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -0.1 °C (low) to 11.2 °C (high). Annual precipitation averages 834.6 Millimeters. Birnamwood is located in USDA Plant Hardiness Zone 4b. 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 | -15.3 °C | -5.4 °C | 28.7 mm |
| February | -14.5 °C | -3.1 °C | 26.42 mm |
| March | -8.2 °C | 3.4 °C | 42.16 mm |
| April | -0.9 °C | 11.1 °C | 76.45 mm |
| May | 5.9 °C | 18.3 °C | 96.01 mm |
| June | 11.5 °C | 23.6 °C | 114.81 mm |
| July | 13.6 °C | 25.8 °C | 96.01 mm |
| August | 12.4 °C | 24.9 °C | 93.98 mm |
| September | 8.1 °C | 20.6 °C | 95.5 mm |
| October | 1.6 °C | 12.8 °C | 77.72 mm |
| November | -4.4 °C | 4.7 °C | 48.01 mm |
| December | -11.2 °C | -2.6 °C | 38.86 mm |
| Annual | -0.1 °C | 11.2 °C | 834.63 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 4b : -31.7°C to -28.9°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 |