West Middlesex, Pennsylvania has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.6 °C (low) to 16.5 °C (high). Annual precipitation averages 1056.9 Millimeters. West Middlesex 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 | -6.9 °C | 2.1 °C | 73.91 mm |
| February | -6.6 °C | 3.8 °C | 58.42 mm |
| March | -2.4 °C | 8.9 °C | 74.68 mm |
| April | 3.2 °C | 16.8 °C | 95.76 mm |
| May | 8.9 °C | 22.6 °C | 97.79 mm |
| June | 13.8 °C | 27.2 °C | 113.54 mm |
| July | 16.2 °C | 29.3 °C | 113.79 mm |
| August | 15.2 °C | 28.5 °C | 91.95 mm |
| September | 11.4 °C | 24.9 °C | 100.84 mm |
| October | 5.5 °C | 18.1 °C | 80.77 mm |
| November | 0.7 °C | 10.8 °C | 75.69 mm |
| December | -3.6 °C | 4.8 °C | 79.76 mm |
| Annual | 4.6 °C | 16.5 °C | 1056.9 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 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |