Chillum, Maryland has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.4 °C (low) to 19.2 °C (high). Annual precipitation averages 1157.7 Millimeters. Chillum is located in USDA Plant Hardiness Zone 7b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -2.9 °C | 6.5 °C | 78.99 mm |
| February | -2.1 °C | 8.3 °C | 68.83 mm |
| March | 1.6 °C | 12.8 °C | 100.33 mm |
| April | 7.1 °C | 19.3 °C | 87.38 mm |
| May | 12.6 °C | 24 °C | 113.79 mm |
| June | 17.7 °C | 28.8 °C | 117.09 mm |
| July | 20.3 °C | 31.3 °C | 115.32 mm |
| August | 19.4 °C | 30.3 °C | 94.23 mm |
| September | 15.7 °C | 26.6 °C | 111.76 mm |
| October | 8.9 °C | 20.2 °C | 96.77 mm |
| November | 3.2 °C | 14.1 °C | 78.74 mm |
| December | -0.6 °C | 8.7 °C | 94.49 mm |
| Annual | 8.4 °C | 19.2 °C | 1157.72 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| 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 |