Sullivan, Ohio has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 40 °F (low) to 59.5 °F (high). Annual precipitation averages 40.2 Inches. Sullivan 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 | 17.8 °F | 33.4 °F | 2.83 in. |
| February | 19.1 °F | 36.1 °F | 2.14 in. |
| March | 27.1 °F | 45.9 °F | 2.94 in. |
| April | 38.0 °F | 59.8 °F | 3.79 in. |
| May | 48.7 °F | 70.4 °F | 4.05 in. |
| June | 58.0 °F | 79.1 °F | 4.31 in. |
| July | 61.3 °F | 82.6 °F | 4.19 in. |
| August | 59.6 °F | 81.2 °F | 3.83 in. |
| September | 52.4 °F | 75.2 °F | 3.38 in. |
| October | 41.6 °F | 62.7 °F | 3.15 in. |
| November | 32.0 °F | 49.4 °F | 2.91 in. |
| December | 23.8 °F | 38.1 °F | 2.7 in. |
| Annual | 40 °F | 59.5 °F | 40.22 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 | Dfb - Humid Continental Mild Summer, Wet All Year |