O'Neill, Nebraska has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 2.5 °C (low) to 15.5 °C (high). Annual precipitation averages 652.3 Millimeters. O'Neill is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11 °C | 0.5 °C | 13.21 mm |
| February | -9.3 °C | 2.7 °C | 15.75 mm |
| March | -4.2 °C | 8.8 °C | 33.53 mm |
| April | 1.7 °C | 14.8 °C | 73.91 mm |
| May | 7.8 °C | 20.8 °C | 101.09 mm |
| June | 13.9 °C | 26.8 °C | 95.25 mm |
| July | 16.8 °C | 30.4 °C | 81.53 mm |
| August | 15.4 °C | 29.1 °C | 81.28 mm |
| September | 10.2 °C | 24.9 °C | 57.66 mm |
| October | 2.7 °C | 16.8 °C | 59.69 mm |
| November | -4.2 °C | 8.7 °C | 22.86 mm |
| December | -9.4 °C | 1.8 °C | 16.51 mm |
| Annual | 2.5 °C | 15.5 °C | 652.27 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Extreme Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |