Barnum, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -1 °C (low) to 10.9 °C (high). Annual precipitation averages 798.8 Millimeters. Barnum 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 | -17.6 °C | -6.6 °C | 20.83 mm |
| February | -15.6 °C | -3.4 °C | 22.35 mm |
| March | -8.7 °C | 3.3 °C | 35.56 mm |
| April | -1.8 °C | 10.7 °C | 64.01 mm |
| May | 4.4 °C | 18.4 °C | 89.15 mm |
| June | 9.8 °C | 23.5 °C | 116.84 mm |
| July | 13.3 °C | 26.5 °C | 117.09 mm |
| August | 12.4 °C | 25.4 °C | 98.04 mm |
| September | 8.1 °C | 20.7 °C | 84.07 mm |
| October | 1.6 °C | 12.6 °C | 78.74 mm |
| November | -5.3 °C | 3.6 °C | 40.64 mm |
| December | -12.8 °C | -3.8 °C | 31.5 mm |
| Annual | -1 °C | 10.9 °C | 798.82 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 |