Jamestown, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.9 °C (low) to 15.2 °C (high). Annual precipitation averages 1121.1 Millimeters. Jamestown is located in USDA Plant Hardiness Zone 6a. 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 | -7.8 °C | 1.1 °C | 80.77 mm |
| February | -7.7 °C | 2.5 °C | 57.91 mm |
| March | -3.4 °C | 7.6 °C | 76.71 mm |
| April | 2.3 °C | 15.2 °C | 101.85 mm |
| May | 8.2 °C | 21.3 °C | 101.6 mm |
| June | 13.2 °C | 25.8 °C | 122.17 mm |
| July | 15.4 °C | 27.8 °C | 117.09 mm |
| August | 14.4 °C | 27 °C | 99.06 mm |
| September | 10.8 °C | 23.6 °C | 108.2 mm |
| October | 5.1 °C | 16.9 °C | 92.2 mm |
| November | 0.3 °C | 9.8 °C | 81.79 mm |
| December | -4.2 °C | 3.8 °C | 81.79 mm |
| Annual | 3.9 °C | 15.2 °C | 1121.14 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°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 |