Portsmouth, Rhode Island has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.4 °C (low) to 15.5 °C (high). Annual precipitation averages 1243.8 Millimeters. Portsmouth is located in USDA Plant Hardiness Zone 7a. 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 | -5.3 °C | 3.3 °C | 106.68 mm |
| February | -4.8 °C | 4.4 °C | 93.98 mm |
| March | -1.3 °C | 8.1 °C | 138.94 mm |
| April | 4.4 °C | 13.8 °C | 118.36 mm |
| May | 9.6 °C | 19.3 °C | 85.09 mm |
| June | 14.9 °C | 24.2 °C | 95.25 mm |
| July | 18.6 °C | 27.6 °C | 80.26 mm |
| August | 17.3 °C | 27 °C | 88.39 mm |
| September | 14.4 °C | 23.4 °C | 93.22 mm |
| October | 7.8 °C | 17.1 °C | 114.3 mm |
| November | 3.2 °C | 11.3 °C | 102.36 mm |
| December | -2 °C | 6.3 °C | 127 mm |
| Annual | 6.4 °C | 15.5 °C | 1243.83 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 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |