Mercersburg, Pennsylvania has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6 °C (low) to 17.9 °C (high). Annual precipitation averages 1167.6 Millimeters. Mercersburg is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.3 °C | 4.4 °C | 79.76 mm |
| February | -4.6 °C | 6.3 °C | 66.8 mm |
| March | -0.6 °C | 11.1 °C | 99.31 mm |
| April | 5 °C | 18 °C | 102.36 mm |
| May | 10.2 °C | 22.9 °C | 115.32 mm |
| June | 15.2 °C | 27.9 °C | 114.3 mm |
| July | 17.8 °C | 30.6 °C | 99.06 mm |
| August | 16.7 °C | 29.4 °C | 112.27 mm |
| September | 12.7 °C | 25.7 °C | 107.19 mm |
| October | 6.3 °C | 19 °C | 102.11 mm |
| November | 1 °C | 12.6 °C | 80.77 mm |
| December | -3 °C | 6.5 °C | 88.39 mm |
| Annual | 6 °C | 17.9 °C | 1167.64 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| 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 |