Willow Lake, South Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.5 °C (low) to 12.1 °C (high). Annual precipitation averages 626.6 Millimeters. Willow Lake is located in USDA Plant Hardiness Zone 4b. 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 | -15.8 °C | -5.6 °C | 13.97 mm |
| February | -13.8 °C | -2.8 °C | 16.51 mm |
| March | -7.2 °C | 4 °C | 26.92 mm |
| April | -0.2 °C | 12.3 °C | 60.2 mm |
| May | 7.1 °C | 19.3 °C | 83.57 mm |
| June | 13.1 °C | 24.8 °C | 104.65 mm |
| July | 15.7 °C | 27.7 °C | 85.09 mm |
| August | 14.3 °C | 26.6 °C | 74.17 mm |
| September | 9.4 °C | 22.3 °C | 67.06 mm |
| October | 1.7 °C | 14.1 °C | 56.39 mm |
| November | -5.8 °C | 5 °C | 21.08 mm |
| December | -12.2 °C | -2.7 °C | 17.02 mm |
| Annual | 0.5 °C | 12.1 °C | 626.63 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 4b : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |