Portland, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.7 °C (low) to 16.6 °C (high). Annual precipitation averages 1286 Millimeters. Portland 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 °C | 2.9 °C | 90.17 mm |
| February | -6.2 °C | 4.8 °C | 73.41 mm |
| March | -2.4 °C | 9.4 °C | 99.82 mm |
| April | 3.2 °C | 16.5 °C | 102.11 mm |
| May | 8.9 °C | 22.1 °C | 106.68 mm |
| June | 14 °C | 26.4 °C | 122.94 mm |
| July | 16.8 °C | 29.1 °C | 119.89 mm |
| August | 15.7 °C | 28.1 °C | 121.16 mm |
| September | 11.8 °C | 24.6 °C | 125.22 mm |
| October | 5.3 °C | 18 °C | 124.71 mm |
| November | -0.1 °C | 11.8 °C | 89.66 mm |
| December | -3.9 °C | 5.9 °C | 110.24 mm |
| Annual | 4.7 °C | 16.6 °C | 1286.01 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 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |