January in Sisak is the cloudiest and the coldest month of the year. In January, the weather in Sisak is typically cold. Average daily high temperature in January is about 3 degrees above zero. On average, Sisak has 15 cloudy, 10 rainy, 4 sunny, and 2 partly cloudy days in January. The rains are usually moderate. January as well as February, March, and December is considered the most uncomfortable time to visit Sisak.