Mellen, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 30.3 °F (low) to 50.8 °F (high). Annual precipitation averages 34.9 Inches. Mellen is located in USDA Plant Hardiness Zone 4a. 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 | 2.5 °F | 20.7 °F | 1.55 in. |
| February | 4.7 °F | 25.9 °F | 1.14 in. |
| March | 15.0 °F | 37.0 °F | 1.73 in. |
| April | 28.1 °F | 49.7 °F | 2.93 in. |
| May | 40.0 °F | 63.9 °F | 3.6 in. |
| June | 50.2 °F | 73.0 °F | 4.36 in. |
| July | 55.5 °F | 77.3 °F | 4.87 in. |
| August | 53.6 °F | 75.7 °F | 3.52 in. |
| September | 46.2 °F | 67.9 °F | 3.73 in. |
| October | 34.6 °F | 53.9 °F | 3.64 in. |
| November | 22.9 °F | 38.3 °F | 2.11 in. |
| December | 10.7 °F | 26.1 °F | 1.71 in. |
| Annual | 30.3 °F | 50.8 °F | 34.89 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 4a : -30°F to -25°F |
| Plant Hardiness Zone - 2012 | Zone 4a : -30°F to -25°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |