| 2023 Hardiness Zone: | Zone 6a: -10°F to -5°F Zone 6b: -5°F to 0°F | |
| 2012 Hardiness Zone: | Zone 6a: -10°F to -5°F | |
| 1990 Hardiness Zone: | Zone 1b: -15F to -10F | |
| Average First Frost Date: | Oct. 11 - Oct. 20 | |
| Average Last Frost Date: | Apr. 11 - Apr. 20 | |
| Koppen-Geiger Climate Zone: | Dfa - Humid Continental Hot Summers | |
| Ecoregion: | 54a - Illinois/Indiana Prairies | |
| Current Drought Status: | Exceptional Drought | |
| Heat Zone Days: | 31 - 45 days Over 86°F |
Annual Climate Data for ZIP Code 61951 - Sullivan, IL | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 18 | 22 | 32 | 42 | 52 | 62 | 65 | 63 | 55 | 44 | 34 | 23 | 43 |
| Avg Max Temp (°F) | 34 | 40 | 52 | 64 | 75 | 84 | 87 | 85 | 79 | 68 | 52 | 39 | 63 |
| Avg Precip (In.) | 2.05 | 2.07 | 3.26 | 3.78 | 4.17 | 4.06 | 4.21 | 3.43 | 3.04 | 2.96 | 3.7 | 2.96 | 39.7 |