May in Banff is the rainiest month of the year. In May, the weather in Banff is typically cold. Average daily high temperature in May is about 6 degrees above zero. On average, Banff has 23 rainy, 5 cloudy, and 3 sunny days in May. The rains are usually heavy. May as well as April, June, and December is considered the most uncomfortable time to visit Banff.