Harmonsburg, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.5 °C (low) to 14.6 °C (high). Annual precipitation averages 1208.3 Millimeters. Harmonsburg 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 | -8.2 °C | 0.7 °C | 94.23 mm |
| February | -8.1 °C | 2.1 °C | 65.28 mm |
| March | -4 °C | 6.9 °C | 83.06 mm |
| April | 1.9 °C | 14.4 °C | 102.62 mm |
| May | 7.8 °C | 20.7 °C | 102.87 mm |
| June | 12.8 °C | 25.1 °C | 126.49 mm |
| July | 15.1 °C | 27.3 °C | 121.67 mm |
| August | 14.2 °C | 26.4 °C | 103.89 mm |
| September | 10.6 °C | 22.9 °C | 114.05 mm |
| October | 4.9 °C | 16.3 °C | 106.93 mm |
| November | 0 °C | 9.4 °C | 90.17 mm |
| December | -4.5 °C | 3.3 °C | 97.03 mm |
| Annual | 3.5 °C | 14.6 °C | 1208.29 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 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |