May weather forecast in National Harbor

May in National Harbor is the rainiest and the cloudiest month of the year. In May, the weather in National Harbor is typically warm. Average daily high temperature in May is about 22 degrees above zero. On average, National Harbor has 16 rainy, 7 sunny, 4 cloudy, and 4 partly cloudy days in May. The rains are usually heavy. May as well as January, February, March, and December is considered the most uncomfortable time to visit National Harbor.