Gretna, Louisiana has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 61.4 °F (low) to 78.5 °F (high). Annual precipitation averages 66.1 Inches. Gretna is located in USDA Plant Hardiness Zone 9b.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 44.6 °F | 62.3 °F | 5.52 in. |
| February | 48.0 °F | 66.0 °F | 4.24 in. |
| March | 54.1 °F | 72.2 °F | 4.62 in. |
| April | 60.6 °F | 78.4 °F | 4.98 in. |
| May | 68.2 °F | 85.4 °F | 5.4 in. |
| June | 74.0 °F | 90.0 °F | 7.2 in. |
| July | 75.8 °F | 91.6 °F | 7.56 in. |
| August | 75.8 °F | 91.4 °F | 7.71 in. |
| September | 72.5 °F | 87.9 °F | 5.78 in. |
| October | 63.2 °F | 80.5 °F | 3.91 in. |
| November | 52.9 °F | 71.0 °F | 4.03 in. |
| December | 47.1 °F | 64.7 °F | 5.12 in. |
| Annual | 61.4 °F | 78.5 °F | 66.07 in. |
| Average First Frost Date | Frost Rare |
| Average Last Frost Date | |
| Average Days With Frost | Frost Rare |
| Plant Hardiness Zone | Zone 9b : 25°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 9b : 25°F to 20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |