Harleysville, Pennsylvania has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.3 °C (low) to 17.6 °C (high). Annual precipitation averages 1209.3 Millimeters. Harleysville is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.4 °C | 4.1 °C | 83.06 mm |
| February | -4.7 °C | 5.6 °C | 70.87 mm |
| March | -0.7 °C | 10.3 °C | 98.55 mm |
| April | 4.9 °C | 17.3 °C | 96.77 mm |
| May | 10.4 °C | 22.7 °C | 103.12 mm |
| June | 15.6 °C | 27.7 °C | 111 mm |
| July | 18.4 °C | 30.3 °C | 117.09 mm |
| August | 17.4 °C | 29.3 °C | 110.49 mm |
| September | 13.4 °C | 25.7 °C | 117.6 mm |
| October | 6.8 °C | 18.8 °C | 109.73 mm |
| November | 1.4 °C | 12.5 °C | 82.04 mm |
| December | -2.5 °C | 6.9 °C | 108.97 mm |
| Annual | 6.3 °C | 17.6 °C | 1209.29 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |