Herndon, Virginia has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.5 °C (low) to 18.7 °C (high). Annual precipitation averages 1132.6 Millimeters. Herndon is located in USDA Plant Hardiness Zone 7b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -3.8 °C | 5.9 °C | 77.47 mm |
| February | -3 °C | 7.7 °C | 67.31 mm |
| March | 0.8 °C | 12.4 °C | 96.52 mm |
| April | 6.4 °C | 18.9 °C | 85.34 mm |
| May | 11.8 °C | 23.4 °C | 114.3 mm |
| June | 16.8 °C | 28.1 °C | 112.52 mm |
| July | 19.5 °C | 30.7 °C | 109.47 mm |
| August | 18.5 °C | 29.7 °C | 90.42 mm |
| September | 14.7 °C | 26 °C | 108.71 mm |
| October | 7.9 °C | 19.6 °C | 97.28 mm |
| November | 2.2 °C | 13.6 °C | 82.3 mm |
| December | -1.6 °C | 8.1 °C | 90.93 mm |
| Annual | 7.5 °C | 18.7 °C | 1132.57 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 7b : -15°C to -12.2°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |