Portland, Tennessee has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.9 °C (low) to 19.9 °C (high). Annual precipitation averages 1357.4 Millimeters. Portland is located in USDA Plant Hardiness Zone 7b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -2.7 °C | 6.9 °C | 109.47 mm |
| February | -1.1 °C | 9.6 °C | 115.06 mm |
| March | 3.3 °C | 14.6 °C | 128.52 mm |
| April | 8.2 °C | 20.4 °C | 123.19 mm |
| May | 13.9 °C | 24.9 °C | 142.24 mm |
| June | 18.2 °C | 29.1 °C | 116.08 mm |
| July | 20.1 °C | 30.9 °C | 119.13 mm |
| August | 19.3 °C | 30.6 °C | 92.46 mm |
| September | 15.3 °C | 27.4 °C | 93.73 mm |
| October | 8.9 °C | 21.4 °C | 93.47 mm |
| November | 3.2 °C | 14.4 °C | 96.01 mm |
| December | -0.3 °C | 9 °C | 128.02 mm |
| Annual | 8.9 °C | 19.9 °C | 1357.38 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7b : -15°C to -12.2°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |