In December, the weather in Châteaulin is typically cold. Average daily high temperature in December is about 9 degrees above zero. On average, Châteaulin has 23 rainy, 4 sunny, 3 cloudy, and 1 partly cloudy day in December. The rains are usually heavy. December as well as January, February, March, and November is considered the most uncomfortable time to visit Châteaulin.