Birnamwood, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 31.8 °F (low) to 52.1 °F (high). Annual precipitation averages 32.9 Inches. 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 | 4.5 °F | 22.2 °F | 1.13 in. |
| February | 5.9 °F | 26.4 °F | 1.04 in. |
| March | 17.2 °F | 38.1 °F | 1.66 in. |
| April | 30.3 °F | 51.9 °F | 3.01 in. |
| May | 42.7 °F | 65.0 °F | 3.78 in. |
| June | 52.7 °F | 74.4 °F | 4.52 in. |
| July | 56.4 °F | 78.5 °F | 3.78 in. |
| August | 54.4 °F | 76.8 °F | 3.7 in. |
| September | 46.5 °F | 69.1 °F | 3.76 in. |
| October | 34.9 °F | 55.1 °F | 3.06 in. |
| November | 24.1 °F | 40.4 °F | 1.89 in. |
| December | 11.8 °F | 27.4 °F | 1.53 in. |
| Annual | 31.8 °F | 52.1 °F | 32.86 in. |
| 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 : -25°F to -20°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |