Merrill, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 36.6 °F (low) to 58.7 °F (high). Annual precipitation averages 28.9 Inches. Merrill is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 9.1 °F | 27.9 °F | 0.61 in. |
| February | 13.1 °F | 32.9 °F | 0.75 in. |
| March | 24.5 °F | 45.8 °F | 1.55 in. |
| April | 35.2 °F | 59.9 °F | 3.17 in. |
| May | 47.9 °F | 71.3 °F | 3.96 in. |
| June | 59.3 °F | 81.8 °F | 4.41 in. |
| July | 62.5 °F | 84.4 °F | 3.21 in. |
| August | 60.0 °F | 82.4 °F | 3.49 in. |
| September | 50.3 °F | 76.0 °F | 3.17 in. |
| October | 37.6 °F | 63.1 °F | 2.47 in. |
| November | 24.7 °F | 46.4 °F | 1.25 in. |
| December | 14.4 °F | 32.8 °F | 0.89 in. |
| Annual | 36.6 °F | 58.7 °F | 28.93 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |