Jefferson, Maryland has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7 °C (low) to 18.2 °C (high). Annual precipitation averages 1090.2 Millimeters. Jefferson is located in USDA Plant Hardiness Zone 7b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.1 °C | 5 °C | 75.95 mm |
| February | -3.3 °C | 6.9 °C | 61.98 mm |
| March | 0.5 °C | 11.6 °C | 91.69 mm |
| April | 5.8 °C | 18.4 °C | 87.38 mm |
| May | 11.2 °C | 23.3 °C | 109.22 mm |
| June | 16.1 °C | 27.9 °C | 101.85 mm |
| July | 18.6 °C | 30.4 °C | 107.44 mm |
| August | 17.5 °C | 29.4 °C | 81.03 mm |
| September | 13.8 °C | 25.6 °C | 114.05 mm |
| October | 7.6 °C | 19.2 °C | 90.68 mm |
| November | 2.1 °C | 13 °C | 78.23 mm |
| December | -1.9 °C | 7.2 °C | 90.68 mm |
| Annual | 7 °C | 18.2 °C | 1090.18 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 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 | Severe Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |