Waltham, Massachusetts has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 4.7 °C (low) to 15.7 °C (high). Annual precipitation averages 1228.3 Millimeters. Waltham is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.7 °C | 2.4 °C | 95.25 mm |
| February | -6.7 °C | 3.8 °C | 85.09 mm |
| March | -2.6 °C | 7.7 °C | 114.81 mm |
| April | 3.2 °C | 14.6 °C | 105.41 mm |
| May | 8.7 °C | 20.4 °C | 95 mm |
| June | 13.8 °C | 25.4 °C | 107.44 mm |
| July | 17.1 °C | 28.6 °C | 91.69 mm |
| August | 16.3 °C | 27.8 °C | 98.55 mm |
| September | 12.1 °C | 23.9 °C | 94.23 mm |
| October | 5.8 °C | 17.2 °C | 121.16 mm |
| November | 0.6 °C | 11.3 °C | 100.84 mm |
| December | -4.1 °C | 5.6 °C | 118.87 mm |
| Annual | 4.7 °C | 15.7 °C | 1228.34 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |