Grantsburg, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -0.3 °C (low) to 12.1 °C (high). Annual precipitation averages 823.5 Millimeters. Grantsburg 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 Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -17.1 °C | -5.6 °C | 19.81 mm |
| February | -15.2 °C | -2.5 °C | 21.34 mm |
| March | -8 °C | 4.6 °C | 39.12 mm |
| April | -0.9 °C | 12.6 °C | 70.87 mm |
| May | 6.1 °C | 20 °C | 104.14 mm |
| June | 11.8 °C | 25.1 °C | 120.14 mm |
| July | 14.3 °C | 27.5 °C | 114.3 mm |
| August | 12.9 °C | 26.4 °C | 104.39 mm |
| September | 8.3 °C | 21.9 °C | 83.06 mm |
| October | 1.7 °C | 13.8 °C | 75.95 mm |
| November | -5.3 °C | 4.6 °C | 41.15 mm |
| December | -12.4 °C | -2.8 °C | 29.21 mm |
| Annual | -0.3 °C | 12.1 °C | 823.48 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| 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 4a : -34.4°C to -31.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |