Bethlehem, Pennsylvania has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.7 °C (low) to 17 °C (high). Annual precipitation averages 1212.6 Millimeters. Bethlehem is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.9 °C | 3.4 °C | 89.66 mm |
| February | -5.2 °C | 5 °C | 69.6 mm |
| March | -1.2 °C | 9.8 °C | 95 mm |
| April | 4.4 °C | 16.7 °C | 93.73 mm |
| May | 10 °C | 22.3 °C | 104.14 mm |
| June | 15.2 °C | 27.1 °C | 119.38 mm |
| July | 17.8 °C | 29.6 °C | 120.4 mm |
| August | 16.8 °C | 28.5 °C | 114.3 mm |
| September | 12.7 °C | 24.8 °C | 118.11 mm |
| October | 6.3 °C | 18.2 °C | 99.06 mm |
| November | 0.9 °C | 12 °C | 83.06 mm |
| December | -2.9 °C | 6.2 °C | 106.17 mm |
| Annual | 5.7 °C | 17 °C | 1212.61 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |