Mount Vernon, Missouri has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 7.5 °C (low) to 19.5 °C (high). Annual precipitation averages 1169.4 Millimeters. Mount Vernon is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.9 °C | 6.2 °C | 63.25 mm |
| February | -3.1 °C | 8.8 °C | 56.9 mm |
| March | 1.7 °C | 14.1 °C | 93.73 mm |
| April | 6.8 °C | 19.3 °C | 118.36 mm |
| May | 12.5 °C | 23.9 °C | 148.59 mm |
| June | 17.5 °C | 28.7 °C | 128.52 mm |
| July | 19.7 °C | 31.4 °C | 95.25 mm |
| August | 18.8 °C | 31.3 °C | 88.39 mm |
| September | 14.2 °C | 27.2 °C | 114.05 mm |
| October | 7.7 °C | 20.9 °C | 92.46 mm |
| November | 1.9 °C | 13.8 °C | 98.04 mm |
| December | -2.9 °C | 8.2 °C | 71.88 mm |
| Annual | 7.5 °C | 19.5 °C | 1169.42 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |