Mount Vernon, Indiana has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.3 °C (low) to 19.3 °C (high). Annual precipitation averages 1179.8 Millimeters. Mount Vernon is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -3.8 °C | 5.1 °C | 89.41 mm |
| February | -2.3 °C | 7.8 °C | 78.49 mm |
| March | 2.2 °C | 13.2 °C | 106.93 mm |
| April | 7.9 °C | 19.7 °C | 128.78 mm |
| May | 13.9 °C | 24.9 °C | 129.29 mm |
| June | 18.7 °C | 29.6 °C | 113.28 mm |
| July | 20.3 °C | 31.1 °C | 100.58 mm |
| August | 18.9 °C | 30.5 °C | 74.42 mm |
| September | 14.8 °C | 27.8 °C | 83.82 mm |
| October | 8.5 °C | 21.2 °C | 84.33 mm |
| November | 2.6 °C | 13.6 °C | 96.77 mm |
| December | -1.6 °C | 7.6 °C | 93.73 mm |
| Annual | 8.3 °C | 19.3 °C | 1179.83 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |