Willow River, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 30 °F (low) to 52 °F (high). Annual precipitation averages 31 Inches. 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 | 0.1 °F | 20.5 °F | 0.82 in. |
| February | 3.7 °F | 26.1 °F | 0.82 in. |
| March | 16.3 °F | 38.3 °F | 1.45 in. |
| April | 28.9 °F | 51.8 °F | 2.44 in. |
| May | 40.4 °F | 65.7 °F | 3.4 in. |
| June | 50.4 °F | 74.8 °F | 4.64 in. |
| July | 55.9 °F | 80.0 °F | 4.47 in. |
| August | 53.9 °F | 77.9 °F | 3.94 in. |
| September | 45.8 °F | 69.6 °F | 3.21 in. |
| October | 34.3 °F | 55.0 °F | 3.01 in. |
| November | 22.0 °F | 38.8 °F | 1.6 in. |
| December | 8.7 °F | 25.5 °F | 1.17 in. |
| Annual | 30 °F | 52 °F | 30.97 in. |
| 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 : -30°F to -25°F |
| Plant Hardiness Zone - 2012 | Zone 3b : -35°F to -30°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |