Gretna, Nebraska has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.7 °C (low) to 16.2 °C (high). Annual precipitation averages 834.9 Millimeters. Gretna is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10 °C | 0.1 °C | 21.08 mm |
| February | -7.9 °C | 2.8 °C | 28.96 mm |
| March | -2 °C | 9.8 °C | 45.72 mm |
| April | 3.8 °C | 16.8 °C | 82.55 mm |
| May | 10.6 °C | 22.4 °C | 125.22 mm |
| June | 16.7 °C | 28.1 °C | 129.03 mm |
| July | 18.7 °C | 29.9 °C | 85.85 mm |
| August | 17.4 °C | 28.8 °C | 102.87 mm |
| September | 12.3 °C | 25.3 °C | 77.72 mm |
| October | 5.4 °C | 18.1 °C | 66.04 mm |
| November | -1.7 °C | 9.6 °C | 36.07 mm |
| December | -7.3 °C | 2.4 °C | 33.78 mm |
| Annual | 4.7 °C | 16.2 °C | 834.89 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 |