Mercersburg, Pennsylvania has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 42.7 °F (low) to 64.2 °F (high). Annual precipitation averages 46 Inches. 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 | 22.5 °F | 40.0 °F | 3.14 in. |
| February | 23.8 °F | 43.4 °F | 2.63 in. |
| March | 30.9 °F | 52.0 °F | 3.91 in. |
| April | 41.0 °F | 64.4 °F | 4.03 in. |
| May | 50.4 °F | 73.3 °F | 4.54 in. |
| June | 59.4 °F | 82.2 °F | 4.5 in. |
| July | 64.0 °F | 87.0 °F | 3.9 in. |
| August | 62.1 °F | 85.0 °F | 4.42 in. |
| September | 54.9 °F | 78.2 °F | 4.22 in. |
| October | 43.4 °F | 66.2 °F | 4.02 in. |
| November | 33.8 °F | 54.6 °F | 3.18 in. |
| December | 26.6 °F | 43.7 °F | 3.48 in. |
| Annual | 42.7 °F | 64.2 °F | 45.97 in. |
| 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 : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |