Grafton, Nebraska has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.2 °C (low) to 17 °C (high). Annual precipitation averages 713 Millimeters. 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 | -9.8 °C | 1.7 °C | 16 mm |
| February | -7.8 °C | 4.1 °C | 18.03 mm |
| March | -2.7 °C | 11.2 °C | 36.07 mm |
| April | 3.1 °C | 17.2 °C | 63.5 mm |
| May | 9.8 °C | 22.7 °C | 122.94 mm |
| June | 15.8 °C | 28.4 °C | 103.63 mm |
| July | 18.2 °C | 30.4 °C | 89.66 mm |
| August | 16.9 °C | 29.3 °C | 89.92 mm |
| September | 11.8 °C | 25.9 °C | 65.02 mm |
| October | 4.6 °C | 18.9 °C | 54.36 mm |
| November | -2.5 °C | 10.6 °C | 30.48 mm |
| December | -7.6 °C | 3.6 °C | 23.37 mm |
| Annual | 4.2 °C | 17 °C | 712.98 mm |
| 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 : -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 | Dfa - Humid Continental Hot Summers With Year Around Precipitation |