Grassflat, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 37 °F (low) to 57.9 °F (high). Annual precipitation averages 43.4 Inches. 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 | 16.3 °F | 32.9 °F | 3.1 in. |
| February | 17.2 °F | 35.9 °F | 2.5 in. |
| March | 24.2 °F | 44.7 °F | 3.42 in. |
| April | 34.6 °F | 58.4 °F | 3.76 in. |
| May | 45.5 °F | 69.0 °F | 3.98 in. |
| June | 53.4 °F | 76.4 °F | 4.22 in. |
| July | 57.5 °F | 80.5 °F | 4.09 in. |
| August | 56.0 °F | 78.9 °F | 4.01 in. |
| September | 48.9 °F | 72.1 °F | 4.23 in. |
| October | 38.6 °F | 60.1 °F | 3.7 in. |
| November | 29.4 °F | 48.4 °F | 3.1 in. |
| December | 22.2 °F | 37.1 °F | 3.3 in. |
| Annual | 37 °F | 57.9 °F | 43.41 in. |
| 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 : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 6a : -10°F to -5°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |