Sullivan, Wisconsin has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3 °C (low) to 13.7 °C (high). Annual precipitation averages 939.5 Millimeters. Sullivan is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.4 °C | -2.6 °C | 42.16 mm |
| February | -9.9 °C | -0.5 °C | 42.16 mm |
| March | -4.3 °C | 6.2 °C | 52.58 mm |
| April | 2 °C | 13.6 °C | 95.5 mm |
| May | 8.4 °C | 20.3 °C | 108.2 mm |
| June | 13.9 °C | 25.8 °C | 128.02 mm |
| July | 16.3 °C | 27.9 °C | 102.36 mm |
| August | 15.3 °C | 26.9 °C | 102.62 mm |
| September | 10.7 °C | 23.2 °C | 84.84 mm |
| October | 4.4 °C | 15.8 °C | 74.93 mm |
| November | -1.9 °C | 7.6 °C | 56.39 mm |
| December | -7.7 °C | 0.5 °C | 49.78 mm |
| Annual | 3 °C | 13.7 °C | 939.54 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |