Letcher, South Dakota has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 1.9 °C (low) to 14.4 °C (high). Annual precipitation averages 624.6 Millimeters. Letcher 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 Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -13.6 °C | -2.8 °C | 13.21 mm |
| February | -11.4 °C | 0.3 °C | 17.53 mm |
| March | -5.4 °C | 6.8 °C | 29.21 mm |
| April | 1.2 °C | 14.7 °C | 72.14 mm |
| May | 8.3 °C | 21.2 °C | 89.41 mm |
| June | 14.4 °C | 26.8 °C | 97.79 mm |
| July | 16.8 °C | 29.8 °C | 75.18 mm |
| August | 15.4 °C | 28.7 °C | 73.66 mm |
| September | 10.3 °C | 24.6 °C | 65.53 mm |
| October | 2.6 °C | 16.3 °C | 52.32 mm |
| November | -4.8 °C | 7.2 °C | 22.35 mm |
| December | -10.9 °C | -0.4 °C | 16.26 mm |
| Annual | 1.9 °C | 14.4 °C | 624.59 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| 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 |