Kirby, Texas has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 14.5 °C (low) to 27 °C (high). Annual precipitation averages 839 Millimeters. Kirby is located in USDA Plant Hardiness Zone 9a. The growing season typically runs from the last frost around Feb. 21 - Feb. 29 through the first frost around Nov. 21 - Nov. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 4.5 °C | 17.4 °C | 51.31 mm |
| February | 6.7 °C | 19.8 °C | 49.78 mm |
| March | 10.5 °C | 23.3 °C | 64.26 mm |
| April | 14.1 °C | 27 °C | 61.98 mm |
| May | 18.9 °C | 30.4 °C | 92.96 mm |
| June | 22.2 °C | 33.6 °C | 85.34 mm |
| July | 23.2 °C | 35.1 °C | 53.85 mm |
| August | 23.2 °C | 35.7 °C | 59.18 mm |
| September | 20.4 °C | 32.6 °C | 93.73 mm |
| October | 15.2 °C | 28.2 °C | 101.35 mm |
| November | 9.5 °C | 22.3 °C | 67.56 mm |
| December | 5.4 °C | 18.2 °C | 57.66 mm |
| Annual | 14.5 °C | 27 °C | 838.96 mm |
| Average First Frost Date | Nov. 21 - Nov. 30 |
| Average Last Frost Date | Feb. 21 - Feb. 29 |
| Average Days With Frost | 10-20 Days |
| Plant Hardiness Zone | Zone 9a : -6.7°C to -3.9°C |
| Plant Hardiness Zone - 2012 | Zone 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |