Grantsville, West Virginia has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.1 °C (low) to 18.3 °C (high). Annual precipitation averages 1232.2 Millimeters. Grantsville is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.9 °C | 5 °C | 89.92 mm |
| February | -4.9 °C | 7 °C | 86.61 mm |
| March | -1.5 °C | 12.2 °C | 113.79 mm |
| April | 4 °C | 19.5 °C | 97.03 mm |
| May | 9.7 °C | 23.8 °C | 132.59 mm |
| June | 14.3 °C | 27.7 °C | 124.97 mm |
| July | 16.8 °C | 29.4 °C | 123.95 mm |
| August | 15.8 °C | 28.9 °C | 102.87 mm |
| September | 12 °C | 26 °C | 96.27 mm |
| October | 5.2 °C | 19.7 °C | 86.61 mm |
| November | -0.5 °C | 13.1 °C | 80.01 mm |
| December | -3.5 °C | 7.2 °C | 97.54 mm |
| Annual | 5.1 °C | 18.3 °C | 1232.16 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |