Terril, Iowa has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 35.7 °F (low) to 55.6 °F (high). Annual precipitation averages 30.9 Inches. Terril 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 | 7.0 °F | 23.9 °F | 0.74 in. |
| February | 10.8 °F | 28.2 °F | 0.82 in. |
| March | 22.7 °F | 41.0 °F | 1.63 in. |
| April | 34.9 °F | 56.5 °F | 3.31 in. |
| May | 47.4 °F | 68.8 °F | 4.44 in. |
| June | 58.2 °F | 78.9 °F | 4.8 in. |
| July | 62.1 °F | 82.9 °F | 3.67 in. |
| August | 59.2 °F | 80.1 °F | 3.69 in. |
| September | 50.9 °F | 74.2 °F | 3.16 in. |
| October | 37.7 °F | 60.0 °F | 2.34 in. |
| November | 24.9 °F | 43.3 °F | 1.35 in. |
| December | 13.0 °F | 29.1 °F | 0.95 in. |
| Annual | 35.7 °F | 55.6 °F | 30.9 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 | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |