In January, the weather in Grande-Synthe is typically cold. Average daily high temperature in January is about 6 degrees above zero. On average, Grande-Synthe has 21 rainy, 5 cloudy, 4 sunny, and 1 partly cloudy day in January. The rains are usually moderate. January as well as February, October, November, and December is considered the most uncomfortable time to visit Grande-Synthe.