Napoleon, North Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -0.9 °C (low) to 11.3 °C (high). Annual precipitation averages 524.8 Millimeters. Napoleon is located in USDA Plant Hardiness Zone 4a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -17.2 °C | -6.8 °C | 13.46 mm |
| February | -14.9 °C | -4.1 °C | 13.97 mm |
| March | -8.4 °C | 2.8 °C | 22.61 mm |
| April | -1.5 °C | 11.8 °C | 36.58 mm |
| May | 5.5 °C | 18.8 °C | 71.88 mm |
| June | 11.6 °C | 23.9 °C | 95.5 mm |
| July | 14.3 °C | 27.4 °C | 84.84 mm |
| August | 12.9 °C | 26.9 °C | 60.2 mm |
| September | 7.8 °C | 22 °C | 47.24 mm |
| October | 0.4 °C | 12.9 °C | 44.7 mm |
| November | -7.3 °C | 3.7 °C | 16.26 mm |
| December | -13.4 °C | -3.9 °C | 17.53 mm |
| Annual | -0.9 °C | 11.3 °C | 524.77 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | Over 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 | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |