Olney, Maryland has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 7.5 °C (low) to 18.1 °C (high). Annual precipitation averages 1172 Millimeters. Olney 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 | -3.8 °C | 5.3 °C | 81.03 mm |
| February | -3 °C | 7.1 °C | 72.14 mm |
| March | 0.8 °C | 11.8 °C | 103.12 mm |
| April | 6.3 °C | 18.4 °C | 89.92 mm |
| May | 11.8 °C | 23.1 °C | 114.3 mm |
| June | 16.6 °C | 27.7 °C | 114.55 mm |
| July | 19.1 °C | 30.1 °C | 110.24 mm |
| August | 18.2 °C | 29 °C | 95 mm |
| September | 14.6 °C | 25.3 °C | 113.28 mm |
| October | 8.1 °C | 18.9 °C | 100.08 mm |
| November | 2.6 °C | 13 °C | 83.06 mm |
| December | -1.4 °C | 7.5 °C | 95.25 mm |
| Annual | 7.5 °C | 18.1 °C | 1171.97 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 |