Grafton, Nebraska has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 39.5 °F (low) to 62.6 °F (high). Annual precipitation averages 28.1 Inches. Grafton is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 14.4 °F | 35.1 °F | 0.63 in. |
| February | 18.0 °F | 39.4 °F | 0.71 in. |
| March | 27.2 °F | 52.2 °F | 1.42 in. |
| April | 37.6 °F | 62.9 °F | 2.5 in. |
| May | 49.7 °F | 72.9 °F | 4.84 in. |
| June | 60.5 °F | 83.1 °F | 4.08 in. |
| July | 64.8 °F | 86.8 °F | 3.53 in. |
| August | 62.4 °F | 84.7 °F | 3.54 in. |
| September | 53.2 °F | 78.7 °F | 2.56 in. |
| October | 40.3 °F | 66.1 °F | 2.14 in. |
| November | 27.5 °F | 51.1 °F | 1.2 in. |
| December | 18.3 °F | 38.4 °F | 0.92 in. |
| Annual | 39.5 °F | 62.6 °F | 28.07 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |