Pennwyn, Pennsylvania has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.4 °C (low) to 17 °C (high). Annual precipitation averages 1276.1 Millimeters. Pennwyn 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.4 °C | 3.6 °C | 91.69 mm |
| February | -4.8 °C | 4.9 °C | 72.9 mm |
| March | -0.6 °C | 9.8 °C | 105.16 mm |
| April | 5.1 °C | 16.9 °C | 99.06 mm |
| May | 10.7 °C | 22.2 °C | 100.33 mm |
| June | 15.8 °C | 27.2 °C | 127 mm |
| July | 18.6 °C | 29.6 °C | 129.29 mm |
| August | 17.6 °C | 28.6 °C | 111.51 mm |
| September | 13.6 °C | 25.1 °C | 131.06 mm |
| October | 7.2 °C | 18.4 °C | 115.57 mm |
| November | 1.8 °C | 11.9 °C | 87.63 mm |
| December | -2.4 °C | 6.2 °C | 104.9 mm |
| Annual | 6.4 °C | 17 °C | 1276.1 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| 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 |