December in Fort Saint John is the most freezing month of the year. In December, the weather in Fort Saint John is typically freezing. Average daily high temperature in December is about 11 degrees below zero. On average, Fort Saint John has 20 cloudy, 7 snowy, 3 sunny, and 1 partly cloudy day in December. The snowfalls are usually light. December as well as January, April, and October is considered the most uncomfortable time to visit Fort Saint John.