In September, the weather in Slovenj Gradec is typically warm. Average daily high temperature in September is about 18 degrees above zero. On average, Slovenj Gradec has 13 rainy, 8 partly cloudy, 7 sunny, and 2 cloudy days in September. The rains are usually heavy. September as well as January, February, March, and April is considered the most uncomfortable time to visit Slovenj Gradec.