May in Longueuil is the rainiest month of the year. In May, the weather in Longueuil is typically warm. Average daily high temperature in May is about 17 degrees above zero. On average, Longueuil has 20 rainy, 7 sunny, 2 cloudy, and 2 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 Longueuil.