Merrillan, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.4 °C (low) to 13 °C (high). Annual precipitation averages 908.6 Millimeters. Merrillan 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 | -15.2 °C | -4.2 °C | 30.23 mm |
| February | -13.4 °C | -1.3 °C | 28.45 mm |
| March | -6.9 °C | 5.4 °C | 45.97 mm |
| April | -0.2 °C | 13.4 °C | 87.12 mm |
| May | 6.4 °C | 20.5 °C | 112.27 mm |
| June | 12.1 °C | 25.5 °C | 131.57 mm |
| July | 14.2 °C | 27.7 °C | 104.39 mm |
| August | 13.1 °C | 26.6 °C | 110.24 mm |
| September | 8.4 °C | 22.5 °C | 96.77 mm |
| October | 2 °C | 15 °C | 75.18 mm |
| November | -4.4 °C | 6 °C | 48.01 mm |
| December | -10.9 °C | -1.3 °C | 38.35 mm |
| Annual | 0.4 °C | 13 °C | 908.55 mm |
| 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 : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |