Mount Gretna, Pennsylvania has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.4 °C (low) to 17 °C (high). Annual precipitation averages 1208.3 Millimeters. Mount Gretna is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.3 °C | 3.4 °C | 83.82 mm |
| February | -5.8 °C | 5.1 °C | 65.53 mm |
| March | -1.6 °C | 9.8 °C | 97.03 mm |
| April | 4.2 °C | 17.1 °C | 92.46 mm |
| May | 9.7 °C | 22.5 °C | 105.92 mm |
| June | 14.9 °C | 26.8 °C | 114.81 mm |
| July | 17.4 °C | 29.6 °C | 120.4 mm |
| August | 16.4 °C | 28.4 °C | 104.14 mm |
| September | 12.5 °C | 24.6 °C | 127.25 mm |
| October | 6.1 °C | 18.3 °C | 114.05 mm |
| November | 0.6 °C | 11.9 °C | 89.15 mm |
| December | -3.5 °C | 5.9 °C | 93.73 mm |
| Annual | 5.4 °C | 17 °C | 1208.29 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| 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 | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |