Duluth, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.2 °C (low) to 9.6 °C (high). Annual precipitation averages 762 Millimeters. Duluth is located in USDA Plant Hardiness Zone 4b. 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 | -15.3 °C | -6 °C | 27.43 mm |
| February | -13.7 °C | -3.5 °C | 25.65 mm |
| March | -7.6 °C | 2.1 °C | 32.51 mm |
| April | -0.8 °C | 8 °C | 64.26 mm |
| May | 4.4 °C | 14.8 °C | 77.47 mm |
| June | 9.6 °C | 19.9 °C | 105.66 mm |
| July | 14.1 °C | 24.2 °C | 97.03 mm |
| August | 14.1 °C | 23.8 °C | 88.65 mm |
| September | 9.5 °C | 19.2 °C | 83.06 mm |
| October | 3.3 °C | 11.7 °C | 77.22 mm |
| November | -3.8 °C | 3.8 °C | 48.51 mm |
| December | -10.9 °C | -3.2 °C | 34.54 mm |
| Annual | 0.2 °C | 9.6 °C | 761.99 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 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 |