Stillwater, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.5 °C (low) to 16 °C (high). Annual precipitation averages 1171.5 Millimeters. Stillwater is located in USDA Plant Hardiness Zone 6b. 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 | -7.3 °C | 2.1 °C | 82.8 mm |
| February | -6.6 °C | 3.6 °C | 61.98 mm |
| March | -2.5 °C | 8.4 °C | 82.55 mm |
| April | 3.2 °C | 16.1 °C | 100.08 mm |
| May | 8.9 °C | 22.1 °C | 105.41 mm |
| June | 13.9 °C | 26.4 °C | 116.84 mm |
| July | 16.3 °C | 28.9 °C | 118.11 mm |
| August | 15.5 °C | 27.9 °C | 110.74 mm |
| September | 11.5 °C | 24.2 °C | 121.67 mm |
| October | 5.3 °C | 17.4 °C | 102.36 mm |
| November | 0.2 °C | 10.7 °C | 80.52 mm |
| December | -3.9 °C | 4.7 °C | 88.39 mm |
| Annual | 4.5 °C | 16 °C | 1171.45 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 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 |