Portsmouth, Rhode Island has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 43.5 °F (low) to 59.9 °F (high). Annual precipitation averages 49 Inches. 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 | 22.5 °F | 38.0 °F | 4.2 in. |
| February | 23.4 °F | 40.0 °F | 3.7 in. |
| March | 29.7 °F | 46.5 °F | 5.47 in. |
| April | 39.9 °F | 56.8 °F | 4.66 in. |
| May | 49.2 °F | 66.8 °F | 3.35 in. |
| June | 58.9 °F | 75.6 °F | 3.75 in. |
| July | 65.4 °F | 81.7 °F | 3.16 in. |
| August | 63.2 °F | 80.6 °F | 3.48 in. |
| September | 58.0 °F | 74.2 °F | 3.67 in. |
| October | 46.0 °F | 62.8 °F | 4.5 in. |
| November | 37.8 °F | 52.4 °F | 4.03 in. |
| December | 28.4 °F | 43.4 °F | 5.0 in. |
| Annual | 43.5 °F | 59.9 °F | 48.97 in. |
| 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 : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 7a : 0°F to 5°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |