Chelsea, Massachusetts has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.3 °C (low) to 15.3 °C (high). Annual precipitation averages 1255.8 Millimeters. Chelsea is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Nov. 11 - Nov. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.8 °C | 2.8 °C | 103.38 mm |
| February | -4.9 °C | 4 °C | 94.49 mm |
| March | -1.2 °C | 7.4 °C | 125.22 mm |
| April | 4.4 °C | 13.7 °C | 111 mm |
| May | 9.7 °C | 19.3 °C | 88.65 mm |
| June | 15.2 °C | 24.6 °C | 103.63 mm |
| July | 18.5 °C | 27.8 °C | 90.93 mm |
| August | 17.9 °C | 26.9 °C | 90.42 mm |
| September | 14 °C | 22.9 °C | 93.22 mm |
| October | 7.8 °C | 16.8 °C | 124.71 mm |
| November | 2.6 °C | 11.1 °C | 104.9 mm |
| December | -2.3 °C | 5.8 °C | 125.22 mm |
| Annual | 6.3 °C | 15.3 °C | 1255.77 mm |
| Average First Frost Date | Nov. 11 - Nov. 20 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 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 | Moderate Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |