Arnold, Maryland has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 9.6 °C (low) to 18.7 °C (high). Annual precipitation averages 1156.2 Millimeters. Arnold is located in USDA Plant Hardiness Zone 8a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -2.3 °C | 6.7 °C | 80.01 mm |
| February | -1.7 °C | 7.8 °C | 69.09 mm |
| March | 2.2 °C | 12.1 °C | 107.19 mm |
| April | 8.1 °C | 18.1 °C | 87.63 mm |
| May | 13.4 °C | 23 °C | 105.92 mm |
| June | 18.8 °C | 28.1 °C | 111.76 mm |
| July | 21.7 °C | 30.5 °C | 109.47 mm |
| August | 20.9 °C | 29.5 °C | 101.6 mm |
| September | 17.4 °C | 25.9 °C | 112.27 mm |
| October | 10.8 °C | 19.8 °C | 97.28 mm |
| November | 4.9 °C | 13.9 °C | 77.98 mm |
| December | 0.4 °C | 8.9 °C | 96.01 mm |
| Annual | 9.6 °C | 18.7 °C | 1156.21 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 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 | Severe Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |