Portsmouth, Ohio has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 6.2 °C (low) to 18.9 °C (high). Annual precipitation averages 1059.7 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 °C | 5.3 °C | 86.61 mm |
| February | -4.1 °C | 7.5 °C | 75.18 mm |
| March | -0.3 °C | 12.8 °C | 99.31 mm |
| April | 5.1 °C | 19.8 °C | 98.3 mm |
| May | 10.8 °C | 24.4 °C | 111.25 mm |
| June | 15.8 °C | 28.6 °C | 105.16 mm |
| July | 17.8 °C | 30.3 °C | 105.66 mm |
| August | 16.9 °C | 30.1 °C | 78.74 mm |
| September | 12.8 °C | 26.9 °C | 81.03 mm |
| October | 6.3 °C | 20.7 °C | 72.39 mm |
| November | 0.4 °C | 13.4 °C | 63.5 mm |
| December | -2.6 °C | 7.5 °C | 82.55 mm |
| Annual | 6.2 °C | 18.9 °C | 1059.68 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 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |