Gretna, Louisiana has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 16.3 °C (low) to 25.8 °C (high). Annual precipitation averages 1678.2 Millimeters. Gretna is located in USDA Plant Hardiness Zone 9b.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 7 °C | 16.8 °C | 140.21 mm |
| February | 8.9 °C | 18.9 °C | 107.7 mm |
| March | 12.3 °C | 22.3 °C | 117.35 mm |
| April | 15.9 °C | 25.8 °C | 126.49 mm |
| May | 20.1 °C | 29.7 °C | 137.16 mm |
| June | 23.3 °C | 32.2 °C | 182.88 mm |
| July | 24.3 °C | 33.1 °C | 192.02 mm |
| August | 24.3 °C | 33 °C | 195.83 mm |
| September | 22.5 °C | 31.1 °C | 146.81 mm |
| October | 17.3 °C | 26.9 °C | 99.31 mm |
| November | 11.6 °C | 21.7 °C | 102.36 mm |
| December | 8.4 °C | 18.2 °C | 130.05 mm |
| Annual | 16.3 °C | 25.8 °C | 1678.17 mm |
| Average First Frost Date | Frost Rare |
| Average Last Frost Date | |
| Average Days With Frost | Frost Rare |
| Plant Hardiness Zone | Zone 9b : -3.9°C to -1.1°C |
| Plant Hardiness Zone - 2012 | Zone 9b : -3.9°C to -1.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |