Portsmouth, Ohio has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 43.1 °F (low) to 66.1 °F (high). Annual precipitation averages 41.7 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 | 23.0 °F | 41.5 °F | 3.41 in. |
| February | 24.7 °F | 45.5 °F | 2.96 in. |
| March | 31.4 °F | 55.1 °F | 3.91 in. |
| April | 41.2 °F | 67.6 °F | 3.87 in. |
| May | 51.5 °F | 76.0 °F | 4.38 in. |
| June | 60.4 °F | 83.5 °F | 4.14 in. |
| July | 64.1 °F | 86.5 °F | 4.16 in. |
| August | 62.5 °F | 86.2 °F | 3.1 in. |
| September | 55.1 °F | 80.4 °F | 3.19 in. |
| October | 43.3 °F | 69.2 °F | 2.85 in. |
| November | 32.7 °F | 56.1 °F | 2.5 in. |
| December | 27.4 °F | 45.5 °F | 3.25 in. |
| Annual | 43.1 °F | 66.1 °F | 41.72 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 6b : -5°F to 0°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |