Harlan, Indiana has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 40.2 °F (low) to 60.1 °F (high). Annual precipitation averages 37 Inches. Harlan is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 17.5 °F | 32.3 °F | 2.31 in. |
| February | 19.1 °F | 35.8 °F | 1.94 in. |
| March | 27.6 °F | 46.8 °F | 2.45 in. |
| April | 37.8 °F | 60.2 °F | 3.6 in. |
| May | 49.3 °F | 71.5 °F | 4.46 in. |
| June | 59.3 °F | 80.4 °F | 3.88 in. |
| July | 62.4 °F | 84.6 °F | 3.74 in. |
| August | 60.3 °F | 82.4 °F | 3.79 in. |
| September | 52.8 °F | 76.7 °F | 2.97 in. |
| October | 41.9 °F | 63.8 °F | 2.67 in. |
| November | 31.8 °F | 49.1 °F | 2.88 in. |
| December | 23.1 °F | 37.2 °F | 2.27 in. |
| Annual | 40.2 °F | 60.1 °F | 36.96 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 6a : -10°F to -5°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |