Mercer, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.9 °C (low) to 15.4 °C (high). Annual precipitation averages 1143.5 Millimeters. Mercer is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.1 °C | 1.2 °C | 84.84 mm |
| February | -7.7 °C | 2.9 °C | 65.02 mm |
| March | -3.4 °C | 8.1 °C | 83.82 mm |
| April | 2.6 °C | 15.6 °C | 103.12 mm |
| May | 8.3 °C | 21.3 °C | 95.5 mm |
| June | 13.3 °C | 25.7 °C | 126.24 mm |
| July | 15.4 °C | 27.9 °C | 121.92 mm |
| August | 14.7 °C | 27.2 °C | 97.28 mm |
| September | 10.9 °C | 23.8 °C | 107.19 mm |
| October | 5 °C | 16.9 °C | 85.34 mm |
| November | 0 °C | 9.8 °C | 84.84 mm |
| December | -4.6 °C | 3.8 °C | 88.39 mm |
| Annual | 3.9 °C | 15.4 °C | 1143.5 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |