May in Dallas is the rainiest month of the year. In May, the weather in Dallas is typically hot. Average daily high temperature in May is about 28 degrees above zero. On average, Dallas has 11 rainy, 10 sunny, 7 partly cloudy, and 3 cloudy days in May. The rains are usually heavy. May as well as January, February, June, and July is considered the most uncomfortable time to visit Dallas.