Grassflat, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.8 °C (low) to 14.4 °C (high). Annual precipitation averages 1102.6 Millimeters. Grassflat 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.7 °C | 0.5 °C | 78.74 mm |
| February | -8.2 °C | 2.2 °C | 63.5 mm |
| March | -4.3 °C | 7.1 °C | 86.87 mm |
| April | 1.4 °C | 14.7 °C | 95.5 mm |
| May | 7.5 °C | 20.6 °C | 101.09 mm |
| June | 11.9 °C | 24.7 °C | 107.19 mm |
| July | 14.2 °C | 26.9 °C | 103.89 mm |
| August | 13.3 °C | 26.1 °C | 101.85 mm |
| September | 9.4 °C | 22.3 °C | 107.44 mm |
| October | 3.7 °C | 15.6 °C | 93.98 mm |
| November | -1.4 °C | 9.1 °C | 78.74 mm |
| December | -5.4 °C | 2.8 °C | 83.82 mm |
| Annual | 2.8 °C | 14.4 °C | 1102.61 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| 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 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |