Hartley, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 35.6 °F (low) to 56.1 °F (high). Annual precipitation averages 30.6 Inches. Hartley 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 | 6.9 °F | 24.5 °F | 0.69 in. |
| February | 11.0 °F | 28.9 °F | 0.8 in. |
| March | 22.7 °F | 41.8 °F | 1.6 in. |
| April | 34.5 °F | 57.2 °F | 3.3 in. |
| May | 47.3 °F | 69.4 °F | 4.33 in. |
| June | 58.3 °F | 79.5 °F | 4.9 in. |
| July | 62.0 °F | 83.1 °F | 3.59 in. |
| August | 59.5 °F | 80.5 °F | 3.43 in. |
| September | 50.6 °F | 74.2 °F | 3.22 in. |
| October | 37.5 °F | 60.5 °F | 2.36 in. |
| November | 24.2 °F | 43.5 °F | 1.45 in. |
| December | 12.9 °F | 29.5 °F | 0.95 in. |
| Annual | 35.6 °F | 56.1 °F | 30.62 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 | Dfa - Humid Continental Hot Summers With Year Around Precipitation |