Merrimac, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 36.5 °F (low) to 56.9 °F (high). Annual precipitation averages 37.3 Inches. Merrimac is located in USDA Plant Hardiness Zone 5a. 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 | 9.6 °F | 27.2 °F | 1.36 in. |
| February | 12.3 °F | 31.6 °F | 1.37 in. |
| March | 22.8 °F | 43.5 °F | 2.08 in. |
| April | 34.7 °F | 57.1 °F | 3.93 in. |
| May | 47.0 °F | 69.4 °F | 4.35 in. |
| June | 57.4 °F | 79.0 °F | 5.43 in. |
| July | 61.2 °F | 82.7 °F | 4.4 in. |
| August | 58.8 °F | 80.8 °F | 4.29 in. |
| September | 50.6 °F | 73.2 °F | 3.58 in. |
| October | 38.9 °F | 60.2 °F | 2.82 in. |
| November | 27.6 °F | 45.0 °F | 2.06 in. |
| December | 16.8 °F | 32.5 °F | 1.64 in. |
| Annual | 36.5 °F | 56.9 °F | 37.31 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |