January in Flensburg is the windiest and the coldest month of the year. In January, the weather in Flensburg is typically cold. Average daily high temperature in January is about 3 degrees above zero. On average, Flensburg has 18 rainy, 8 cloudy, 4 sunny, and 1 partly cloudy day in January. The rains are usually moderate. January as well as February, March, September, and October is considered the most uncomfortable time to visit Flensburg.