May in Waterbury is the rainiest and the cloudiest month of the year. In May, the weather in Waterbury is typically warm. Average daily high temperature in May is about 18 degrees above zero. On average, Waterbury has 17 rainy, 6 sunny, 5 partly cloudy, and 3 cloudy days in May. The rains are usually heavy. May as well as February, March, and December is considered the most uncomfortable time to visit Waterbury.