| 2023 Hardiness Zone: | 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. 21 - Oct. 31 |
| Average Last Frost Date: | Apr. 11 - Apr. 20 |
| Koppen-Geiger Climate Zone: | Dfa - Humid Continental Hot Summers |
| Ecoregion: | 72j - Southern Illinoian Till Plain |
| Heat Zone Days: | 31 - 45 days Over 86°F |
Annual Climate Data for ZIP Code 62471 - Vandalia, IL | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 18 | 23 | 32 | 43 | 53 | 62 | 66 | 63 | 55 | 44 | 34 | 24 | 43 |
| Avg Max Temp (°F) | 35 | 41 | 52 | 64 | 75 | 84 | 87 | 86 | 79 | 68 | 52 | 40 | 64 |
| Avg Precip (In.) | 2.24 | 2.32 | 3.65 | 3.95 | 4.36 | 4.16 | 3.85 | 3.11 | 3.12 | 2.99 | 3.95 | 3.15 | 40.84 |