Sullivan, Missouri has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.3 °C (low) to 18.9 °C (high). Annual precipitation averages 1138.7 Millimeters. Sullivan is located in USDA Plant Hardiness Zone 6b. 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 | -5.6 °C | 4.8 °C | 67.06 mm |
| February | -3.7 °C | 7.7 °C | 65.02 mm |
| March | 1 °C | 13.1 °C | 94.23 mm |
| April | 7 °C | 19.6 °C | 125.98 mm |
| May | 12.6 °C | 24.3 °C | 131.57 mm |
| June | 17.4 °C | 28.7 °C | 110.49 mm |
| July | 19.7 °C | 31.1 °C | 106.43 mm |
| August | 18.7 °C | 30.7 °C | 100.08 mm |
| September | 14.3 °C | 26.7 °C | 94.49 mm |
| October | 7.8 °C | 20.5 °C | 85.09 mm |
| November | 1.8 °C | 13.1 °C | 91.44 mm |
| December | -3.1 °C | 7 °C | 66.8 mm |
| Annual | 7.3 °C | 18.9 °C | 1138.68 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |