September in Longueuil is the sunniest month of the year. In September, the weather in Longueuil is typically warm. Average daily high temperature in September is about 20 degrees above zero. On average, Longueuil has 15 sunny, 7 rainy, 7 partly cloudy, and 1 cloudy day in September. The rains are usually heavy. September as well as {{month_nom: February}}, and {{month_nom: February}} is considered the most comfortable time to visit Longueuil.