Kirby, Arkansas has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 9.5 °C (low) to 22.5 °C (high). Annual precipitation averages 1476.8 Millimeters. Kirby is located in USDA Plant Hardiness Zone 8a. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -1.4 °C | 11 °C | 102.87 mm |
| February | 0.2 °C | 13.4 °C | 106.43 mm |
| March | 4.1 °C | 18 °C | 134.87 mm |
| April | 8.7 °C | 22.7 °C | 145.8 mm |
| May | 14.2 °C | 26.3 °C | 167.13 mm |
| June | 18.7 °C | 30.8 °C | 112.78 mm |
| July | 20.4 °C | 33 °C | 113.54 mm |
| August | 19.8 °C | 32.9 °C | 92.2 mm |
| September | 15.9 °C | 29.3 °C | 105.41 mm |
| October | 9.3 °C | 23.6 °C | 132.08 mm |
| November | 3.8 °C | 17.2 °C | 124.46 mm |
| December | 0.1 °C | 12.3 °C | 139.19 mm |
| Annual | 9.5 °C | 22.5 °C | 1476.76 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 8a : -12.2°C to -9.4°C |
| Plant Hardiness Zone - 2012 | Zone 7b : -15°C to -12.2°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |