Merrimac, Virginia has a Temperate Oceanic Climate climate (Köppen classification: Cfb). Average annual temperatures range from 42.9 °F (low) to 64.2 °F (high). Annual precipitation averages 42.1 Inches. Merrimac is located in USDA Plant Hardiness Zone 7a. 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 | 23.7 °F | 42.6 °F | 3.07 in. |
| February | 26.0 °F | 46.2 °F | 2.78 in. |
| March | 32.2 °F | 54.5 °F | 3.63 in. |
| April | 41.5 °F | 65.0 °F | 3.81 in. |
| May | 50.7 °F | 73.0 °F | 4.46 in. |
| June | 58.7 °F | 79.8 °F | 4.17 in. |
| July | 62.6 °F | 83.0 °F | 3.95 in. |
| August | 61.4 °F | 82.0 °F | 3.51 in. |
| September | 54.7 °F | 76.4 °F | 3.56 in. |
| October | 43.3 °F | 66.4 °F | 2.99 in. |
| November | 32.8 °F | 55.6 °F | 2.87 in. |
| December | 27.2 °F | 46.0 °F | 3.31 in. |
| Annual | 42.9 °F | 64.2 °F | 42.11 in. |
| 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 7a : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Cfb - Temperate Oceanic Climate |