Alpharetta, Georgia has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 9.7 °C (low) to 21.6 °C (high). Annual precipitation averages 1370.3 Millimeters. Alpharetta 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. 11 - Nov. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -0.7 °C | 10.6 °C | 125.98 mm |
| February | 0.9 °C | 12.9 °C | 123.19 mm |
| March | 4.4 °C | 17.4 °C | 130.05 mm |
| April | 8.7 °C | 22.1 °C | 109.98 mm |
| May | 13.8 °C | 26.1 °C | 101.6 mm |
| June | 18.3 °C | 29.4 °C | 108.97 mm |
| July | 20.2 °C | 31.1 °C | 127.76 mm |
| August | 19.8 °C | 30.8 °C | 107.95 mm |
| September | 16.3 °C | 27.9 °C | 112.52 mm |
| October | 9.9 °C | 22.5 °C | 94.49 mm |
| November | 3.8 °C | 16.6 °C | 108.2 mm |
| December | 1.1 °C | 12 °C | 119.63 mm |
| Annual | 9.7 °C | 21.6 °C | 1370.32 mm |
| Average First Frost Date | Nov. 11 - Nov. 20 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 40-50 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 | Moderate Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |