Willow Lake, South Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 32.9 °F (low) to 53.8 °F (high). Annual precipitation averages 24.7 Inches. 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 | 3.5 °F | 22.0 °F | 0.55 in. |
| February | 7.1 °F | 26.9 °F | 0.65 in. |
| March | 19.1 °F | 39.2 °F | 1.06 in. |
| April | 31.7 °F | 54.2 °F | 2.37 in. |
| May | 44.7 °F | 66.8 °F | 3.29 in. |
| June | 55.5 °F | 76.6 °F | 4.12 in. |
| July | 60.3 °F | 81.8 °F | 3.35 in. |
| August | 57.7 °F | 79.9 °F | 2.92 in. |
| September | 49.0 °F | 72.2 °F | 2.64 in. |
| October | 35.1 °F | 57.3 °F | 2.22 in. |
| November | 21.6 °F | 41.0 °F | 0.83 in. |
| December | 10.0 °F | 27.2 °F | 0.67 in. |
| Annual | 32.9 °F | 53.8 °F | 24.67 in. |
| 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 : -25°F to -20°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |