In December, the weather in St Catharines is typically cold. Average daily high temperature in December is about 2 degrees above zero. On average, St Catharines has 15 rainy, 12 cloudy, 2 snowy, and 2 sunny days in December. The rains are usually moderate. December as well as March, April, October, and November is considered the most uncomfortable time to visit St Catharines.