Willow River, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -1.1 °C (low) to 11.1 °C (high). Annual precipitation averages 786.7 Millimeters. Willow River is located in USDA Plant Hardiness Zone 4a. 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 | -17.7 °C | -6.4 °C | 20.83 mm |
| February | -15.7 °C | -3.3 °C | 20.83 mm |
| March | -8.7 °C | 3.5 °C | 36.83 mm |
| April | -1.7 °C | 11 °C | 61.98 mm |
| May | 4.7 °C | 18.7 °C | 86.36 mm |
| June | 10.2 °C | 23.8 °C | 117.86 mm |
| July | 13.3 °C | 26.7 °C | 113.54 mm |
| August | 12.2 °C | 25.5 °C | 100.08 mm |
| September | 7.7 °C | 20.9 °C | 81.53 mm |
| October | 1.3 °C | 12.8 °C | 76.45 mm |
| November | -5.6 °C | 3.8 °C | 40.64 mm |
| December | -12.9 °C | -3.6 °C | 29.72 mm |
| Annual | -1.1 °C | 11.1 °C | 786.65 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 4a : -34.4°C to -31.7°C |
| Plant Hardiness Zone - 2012 | Zone 3b : -37.2°C to -34.4°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |