March in Mount Vernon is the rainiest month of the year. In March, the weather in Mount Vernon is typically warm. Average daily high temperature in March is about 9 degrees above zero. On average, Mount Vernon has 19 rainy, 5 sunny, 4 partly cloudy, and 3 cloudy days in March. The rains are usually heavy. March as well as January, February, April, and October is considered the most uncomfortable time to visit Mount Vernon.