Mount Vernon, South Dakota has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 2 °C (low) to 14.5 °C (high). Annual precipitation averages 629.4 Millimeters. Mount Vernon is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -13.3 °C | -2.6 °C | 13.21 mm |
| February | -11.1 °C | 0.4 °C | 18.8 mm |
| March | -5.3 °C | 6.9 °C | 29.21 mm |
| April | 1.3 °C | 14.5 °C | 73.41 mm |
| May | 8.2 °C | 21.1 °C | 89.92 mm |
| June | 14.4 °C | 26.8 °C | 96.77 mm |
| July | 16.8 °C | 29.9 °C | 75.95 mm |
| August | 15.6 °C | 28.8 °C | 72.9 mm |
| September | 10.5 °C | 24.6 °C | 66.55 mm |
| October | 2.7 °C | 16.2 °C | 52.83 mm |
| November | -4.7 °C | 7.2 °C | 22.61 mm |
| December | -10.7 °C | -0.3 °C | 17.27 mm |
| Annual | 2 °C | 14.5 °C | 629.43 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |