| 2023 Hardiness Zone: | Zone 6b: -5°F to 0°F |
| 2012 Hardiness Zone: | Zone 6a: -10°F to -5°F Zone 6b: -5°F to 0°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: | 72j - Southern Illinoian Till Plain |
| Heat Zone Days: | 61 - 90 days Over 86°F |
Annual Climate Data for ZIP Code 62864 - Mount Vernon, IL | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 19 | 23 | 33 | 43 | 53 | 62 | 66 | 64 | 56 | 44 | 34 | 24 | 43 |
| Avg Max Temp (°F) | 37 | 43 | 54 | 65 | 75 | 84 | 88 | 86 | 79 | 68 | 54 | 42 | 65 |
| Avg Precip (In.) | 2.48 | 2.66 | 3.97 | 4.4 | 4.55 | 3.72 | 3.67 | 3.19 | 3.11 | 2.99 | 4.33 | 3.27 | 42.34 |