Merrill, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -0.3 °C (low) to 11.3 °C (high). Annual precipitation averages 851.7 Millimeters. 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 | -15.7 °C | -5.4 °C | 29.46 mm |
| February | -14.8 °C | -3 °C | 26.92 mm |
| March | -8.4 °C | 3.5 °C | 43.69 mm |
| April | -1.1 °C | 11.3 °C | 74.93 mm |
| May | 5.9 °C | 18.8 °C | 93.98 mm |
| June | 11.6 °C | 23.9 °C | 116.33 mm |
| July | 13.7 °C | 26.2 °C | 97.03 mm |
| August | 12.4 °C | 25.1 °C | 103.63 mm |
| September | 7.9 °C | 20.8 °C | 97.54 mm |
| October | 1.5 °C | 12.9 °C | 80.01 mm |
| November | -4.8 °C | 4.3 °C | 49.78 mm |
| December | -11.4 °C | -2.6 °C | 38.35 mm |
| Annual | -0.3 °C | 11.3 °C | 851.65 mm |
| 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 : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4a : -34.4°C to -31.7°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |