Plymouth, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.7 °C (low) to 16.4 °C (high). Annual precipitation averages 1100.3 Millimeters. Plymouth is located in USDA Plant Hardiness Zone 6b. 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 | -7.2 °C | 2.2 °C | 69.09 mm |
| February | -6.7 °C | 3.8 °C | 61.72 mm |
| March | -2.4 °C | 8.6 °C | 72.14 mm |
| April | 3.3 °C | 16 °C | 91.44 mm |
| May | 9.1 °C | 22.4 °C | 93.47 mm |
| June | 14.2 °C | 26.8 °C | 117.09 mm |
| July | 16.6 °C | 29.6 °C | 111.76 mm |
| August | 15.7 °C | 28.4 °C | 100.08 mm |
| September | 11.7 °C | 24.6 °C | 119.63 mm |
| October | 5.4 °C | 17.6 °C | 108.46 mm |
| November | 0.4 °C | 11.1 °C | 74.68 mm |
| December | -3.8 °C | 5.1 °C | 80.77 mm |
| Annual | 4.7 °C | 16.4 °C | 1100.33 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 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |