Merrill, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 31.5 °F (low) to 52.4 °F (high). Annual precipitation averages 33.5 Inches. Merrill 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 Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 3.8 °F | 22.2 °F | 1.16 in. |
| February | 5.4 °F | 26.6 °F | 1.06 in. |
| March | 16.9 °F | 38.3 °F | 1.72 in. |
| April | 30.0 °F | 52.3 °F | 2.95 in. |
| May | 42.7 °F | 65.8 °F | 3.7 in. |
| June | 52.9 °F | 75.1 °F | 4.58 in. |
| July | 56.6 °F | 79.2 °F | 3.82 in. |
| August | 54.3 °F | 77.1 °F | 4.08 in. |
| September | 46.2 °F | 69.5 °F | 3.84 in. |
| October | 34.7 °F | 55.2 °F | 3.15 in. |
| November | 23.4 °F | 39.8 °F | 1.96 in. |
| December | 11.5 °F | 27.4 °F | 1.51 in. |
| Annual | 31.5 °F | 52.4 °F | 33.53 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 4b : -25°F to -20°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 |