Mount Calm, Texas has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 13 °C (low) to 25.2 °C (high). Annual precipitation averages 985.5 Millimeters. Mount Calm is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Mar. 11 - Mar. 20 through the first frost around Nov. 11 - Nov. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 2.2 °C | 14.4 °C | 71.88 mm |
| February | 4.3 °C | 16.7 °C | 71.37 mm |
| March | 8.2 °C | 20.4 °C | 91.95 mm |
| April | 12.3 °C | 24.7 °C | 86.87 mm |
| May | 17.3 °C | 28.7 °C | 116.08 mm |
| June | 21.4 °C | 32.9 °C | 94.74 mm |
| July | 23.1 °C | 35.2 °C | 44.2 mm |
| August | 23 °C | 35.6 °C | 61.21 mm |
| September | 19.3 °C | 32.2 °C | 77.98 mm |
| October | 13.4 °C | 26.5 °C | 112.52 mm |
| November | 7.8 °C | 20 °C | 76.96 mm |
| December | 3.3 °C | 15.3 °C | 79.76 mm |
| Annual | 13 °C | 25.2 °C | 985.52 mm |
| Average First Frost Date | Nov. 11 - Nov. 20 |
| Average Last Frost Date | Mar. 11 - Mar. 20 |
| Average Days With Frost | 30-40 Days |
| Plant Hardiness Zone | Zone 8b : -9.4°C to -6.7°C |
| Plant Hardiness Zone - 2012 | Zone 8a : -12.2°C to -9.4°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |