Willmar, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.9 °C (low) to 11.8 °C (high). Annual precipitation averages 747 Millimeters. Willmar 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 | -16.1 °C | -6.2 °C | 18.03 mm |
| February | -14.2 °C | -3.7 °C | 20.32 mm |
| March | -6.9 °C | 3.3 °C | 36.58 mm |
| April | 0.6 °C | 12.2 °C | 65.02 mm |
| May | 7.8 °C | 19.8 °C | 86.87 mm |
| June | 13.9 °C | 25.1 °C | 121.16 mm |
| July | 16.2 °C | 27.3 °C | 100.33 mm |
| August | 14.5 °C | 26.1 °C | 104.65 mm |
| September | 9.7 °C | 22.3 °C | 74.93 mm |
| October | 2.4 °C | 13.9 °C | 62.23 mm |
| November | -4.9 °C | 4.6 °C | 32.77 mm |
| December | -12 °C | -3.2 °C | 24.13 mm |
| Annual | 0.9 °C | 11.8 °C | 747.02 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 | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |