Mercer, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 29.6 °F (low) to 50.2 °F (high). Annual precipitation averages 33.1 Inches. Mercer is located in USDA Plant Hardiness Zone 4a. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.5 °F | 20.8 °F | 1.33 in. |
| February | 3.1 °F | 25.8 °F | 1.25 in. |
| March | 13.7 °F | 37.1 °F | 1.63 in. |
| April | 27.2 °F | 49.3 °F | 2.7 in. |
| May | 41.0 °F | 63.1 °F | 3.66 in. |
| June | 50.6 °F | 72.6 °F | 4.53 in. |
| July | 55.1 °F | 76.6 °F | 3.98 in. |
| August | 52.5 °F | 74.8 °F | 3.57 in. |
| September | 45.3 °F | 66.5 °F | 3.35 in. |
| October | 33.4 °F | 52.6 °F | 3.53 in. |
| November | 21.8 °F | 37.7 °F | 2.03 in. |
| December | 9.4 °F | 25.6 °F | 1.56 in. |
| Annual | 29.6 °F | 50.2 °F | 33.12 in. |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | Over 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 |