Grafton, North Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 29.6 °F (low) to 49.6 °F (high). Annual precipitation averages 21.3 Inches. Grafton 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 | -2.7 °F | 14.1 °F | 0.51 in. |
| February | 0.6 °F | 19.1 °F | 0.48 in. |
| March | 14.5 °F | 31.9 °F | 0.85 in. |
| April | 30.0 °F | 50.7 °F | 1.1 in. |
| May | 42.5 °F | 65.7 °F | 3.18 in. |
| June | 54.2 °F | 75.5 °F | 3.86 in. |
| July | 57.7 °F | 79.9 °F | 3.23 in. |
| August | 54.6 °F | 79.4 °F | 2.72 in. |
| September | 45.7 °F | 70.0 °F | 2.08 in. |
| October | 33.7 °F | 53.6 °F | 1.66 in. |
| November | 18.9 °F | 35.0 °F | 0.87 in. |
| December | 5.3 °F | 20.5 °F | 0.73 in. |
| Annual | 29.6 °F | 49.6 °F | 21.27 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 |