Mercer, Tennessee has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 9.9 °C (low) to 21.4 °C (high). Annual precipitation averages 1423.2 Millimeters. Mercer is located in USDA Plant Hardiness Zone 8a. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -1.4 °C | 8.5 °C | 108.71 mm |
| February | 0.4 °C | 11.3 °C | 126.24 mm |
| March | 4.5 °C | 16.2 °C | 143.51 mm |
| April | 9.4 °C | 22.1 °C | 137.92 mm |
| May | 14.9 °C | 26.4 °C | 139.95 mm |
| June | 19.4 °C | 30.5 °C | 115.57 mm |
| July | 21.2 °C | 32.1 °C | 110.24 mm |
| August | 20.2 °C | 31.8 °C | 88.39 mm |
| September | 16.2 °C | 28.8 °C | 101.35 mm |
| October | 9.4 °C | 23.1 °C | 100.33 mm |
| November | 3.9 °C | 16.2 °C | 111.51 mm |
| December | 0.3 °C | 10.3 °C | 139.45 mm |
| Annual | 9.9 °C | 21.4 °C | 1423.17 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 8a : -12.2°C to -9.4°C |
| Plant Hardiness Zone - 2012 | Zone 7b : -15°C to -12.2°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |