Harmonsburg, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 38.4 °F (low) to 58.3 °F (high). Annual precipitation averages 47.6 Inches. 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 | 17.3 °F | 33.2 °F | 3.71 in. |
| February | 17.4 °F | 35.7 °F | 2.57 in. |
| March | 24.8 °F | 44.5 °F | 3.27 in. |
| April | 35.5 °F | 58.0 °F | 4.04 in. |
| May | 46.1 °F | 69.3 °F | 4.05 in. |
| June | 55.0 °F | 77.2 °F | 4.98 in. |
| July | 59.2 °F | 81.1 °F | 4.79 in. |
| August | 57.6 °F | 79.5 °F | 4.09 in. |
| September | 51.1 °F | 73.3 °F | 4.49 in. |
| October | 40.9 °F | 61.3 °F | 4.21 in. |
| November | 32.0 °F | 48.9 °F | 3.55 in. |
| December | 23.9 °F | 38.0 °F | 3.82 in. |
| Annual | 38.4 °F | 58.3 °F | 47.57 in. |
| 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 : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |