Napoleon, North Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 30.5 °F (low) to 52.3 °F (high). Annual precipitation averages 20.7 Inches. 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 | 1.0 °F | 19.7 °F | 0.53 in. |
| February | 5.1 °F | 24.7 °F | 0.55 in. |
| March | 16.9 °F | 37.0 °F | 0.89 in. |
| April | 29.3 °F | 53.2 °F | 1.44 in. |
| May | 41.9 °F | 65.8 °F | 2.83 in. |
| June | 52.8 °F | 75.1 °F | 3.76 in. |
| July | 57.8 °F | 81.3 °F | 3.34 in. |
| August | 55.3 °F | 80.5 °F | 2.37 in. |
| September | 46.0 °F | 71.6 °F | 1.86 in. |
| October | 32.7 °F | 55.3 °F | 1.76 in. |
| November | 18.9 °F | 38.6 °F | 0.64 in. |
| December | 7.8 °F | 25.0 °F | 0.69 in. |
| Annual | 30.5 °F | 52.3 °F | 20.66 in. |
| 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 : -30°F to -25°F |
| Plant Hardiness Zone - 2012 | Zone 4a : -30°F to -25°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |