Herndon, Pennsylvania has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 40.7 °F (low) to 61.1 °F (high). Annual precipitation averages 44.5 Inches. Herndon is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 19.5 °F | 35.9 °F | 3.06 in. |
| February | 20.7 °F | 38.9 °F | 2.41 in. |
| March | 28.2 °F | 48.1 °F | 3.38 in. |
| April | 38.4 °F | 61.1 °F | 3.81 in. |
| May | 48.7 °F | 71.4 °F | 3.89 in. |
| June | 58.1 °F | 79.8 °F | 4.31 in. |
| July | 62.1 °F | 84.3 °F | 4.4 in. |
| August | 60.5 °F | 82.4 °F | 4.03 in. |
| September | 53.1 °F | 75.7 °F | 4.64 in. |
| October | 41.9 °F | 63.5 °F | 4.04 in. |
| November | 32.3 °F | 51.6 °F | 3.15 in. |
| December | 25.1 °F | 40.5 °F | 3.36 in. |
| Annual | 40.7 °F | 61.1 °F | 44.48 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6b : -5°F to 0°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |