Napoleon, Michigan has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.5 °C (low) to 14.5 °C (high). Annual precipitation averages 904.8 Millimeters. Napoleon is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9 °C | -0.6 °C | 59.69 mm |
| February | -8.5 °C | 1.2 °C | 50.29 mm |
| March | -3.9 °C | 6.8 °C | 59.18 mm |
| April | 2.2 °C | 14.3 °C | 83.57 mm |
| May | 8.6 °C | 20.8 °C | 99.57 mm |
| June | 13.8 °C | 26 °C | 93.73 mm |
| July | 15.7 °C | 28.1 °C | 87.12 mm |
| August | 14.8 °C | 27.1 °C | 89.66 mm |
| September | 10.6 °C | 23.6 °C | 79.5 mm |
| October | 4.4 °C | 16.3 °C | 76.2 mm |
| November | -0.9 °C | 8.7 °C | 69.34 mm |
| December | -5.4 °C | 2.2 °C | 56.9 mm |
| Annual | 3.5 °C | 14.5 °C | 904.75 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |