May in Pontiac is the rainiest month of the year. In May, the weather in Pontiac is typically warm. Average daily high temperature in May is about 18 degrees above zero. On average, Pontiac has 17 rainy, 8 sunny, 3 cloudy, and 3 partly cloudy days in May. The rains are usually heavy. May as well as March, April, October, and November is considered the most uncomfortable time to visit Pontiac.