Casselman, Pennsylvania has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 2.9 °C (low) to 15.1 °C (high). Annual precipitation averages 1179.6 Millimeters. Casselman 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. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.3 °C | 1.7 °C | 90.93 mm |
| February | -7.6 °C | 3.3 °C | 81.79 mm |
| March | -3.9 °C | 8.1 °C | 101.09 mm |
| April | 1.7 °C | 15.6 °C | 102.11 mm |
| May | 7.3 °C | 20.8 °C | 120.4 mm |
| June | 12 °C | 25.1 °C | 119.63 mm |
| July | 14.2 °C | 27.1 °C | 109.47 mm |
| August | 13.4 °C | 26.4 °C | 100.33 mm |
| September | 9.4 °C | 23 °C | 96.77 mm |
| October | 3.5 °C | 16.6 °C | 83.82 mm |
| November | -1.7 °C | 9.7 °C | 80.26 mm |
| December | -5.4 °C | 4.1 °C | 92.96 mm |
| Annual | 2.9 °C | 15.1 °C | 1179.56 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 11 - May 20 |
| 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 | Dfa - Humid Continental Hot Summers With Year Around Precipitation |