Mahnomen, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 30.3 °F (low) to 50.2 °F (high). Annual precipitation averages 25.4 Inches. Mahnomen 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 | -1.4 °F | 16.3 °F | 0.86 in. |
| February | 1.3 °F | 21.0 °F | 0.7 in. |
| March | 16.0 °F | 34.4 °F | 1.02 in. |
| April | 30.4 °F | 51.2 °F | 1.53 in. |
| May | 42.7 °F | 65.6 °F | 3.0 in. |
| June | 54.0 °F | 74.7 °F | 4.58 in. |
| July | 57.9 °F | 79.0 °F | 3.55 in. |
| August | 55.3 °F | 78.2 °F | 2.92 in. |
| September | 46.6 °F | 69.5 °F | 2.95 in. |
| October | 34.4 °F | 53.8 °F | 2.36 in. |
| November | 20.0 °F | 36.3 °F | 0.95 in. |
| December | 6.1 °F | 22.5 °F | 1.01 in. |
| Annual | 30.3 °F | 50.2 °F | 25.43 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 |