Dennison, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.8 °C (low) to 12.6 °C (high). Annual precipitation averages 856.8 Millimeters. Dennison is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -14.5 °C | -4.9 °C | 22.86 mm |
| February | -12.6 °C | -2.2 °C | 25.15 mm |
| March | -5.7 °C | 4.6 °C | 46.23 mm |
| April | 1.3 °C | 13.2 °C | 73.91 mm |
| May | 8.3 °C | 20.1 °C | 111.51 mm |
| June | 14.2 °C | 25.4 °C | 132.59 mm |
| July | 16.2 °C | 27.4 °C | 103.63 mm |
| August | 14.8 °C | 26.4 °C | 117.35 mm |
| September | 10.2 °C | 22.6 °C | 86.87 mm |
| October | 3.1 °C | 14.8 °C | 62.74 mm |
| November | -3.7 °C | 5.7 °C | 42.67 mm |
| December | -10.6 °C | -1.8 °C | 31.24 mm |
| Annual | 1.8 °C | 12.6 °C | 856.75 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |