| 2023 Hardiness Zone: | Zone 6a: -10°F to -5°F |
| 2012 Hardiness Zone: | Zone 6a: -10°F to -5°F Zone 5b: -15°F to -10°F |
| 1990 Hardiness Zone: | Zone 1b: -15F to -10F |
| Average First Frost Date: | Oct. 11 - Oct. 20 |
| Average Last Frost Date: | Apr. 21 - Apr. 30 |
| Koppen-Geiger Climate Zone: | Dfa - Humid Continental Hot Summers |
| Ecoregion: | 54a - Illinois/Indiana Prairies |
| Heat Zone Days: | 31 - 45 days Over 86°F |
Annual Climate Data for ZIP Code 62629 - Chatham, IL | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 17 | 22 | 32 | 42 | 53 | 62 | 66 | 63 | 55 | 44 | 33 | 23 | 43 |
| Avg Max Temp (°F) | 34 | 40 | 52 | 64 | 75 | 84 | 87 | 85 | 79 | 68 | 52 | 39 | 63 |
| Avg Precip (In.) | 1.77 | 1.93 | 3.2 | 3.63 | 4.29 | 3.85 | 3.72 | 3.33 | 3.02 | 2.69 | 3.2 | 2.6 | 37.24 |