In September, the weather in Jablonec nad Jizerou is typically warm. Average daily high temperature in September is about 16 degrees above zero. On average, Jablonec nad Jizerou has 14 rainy, 8 partly cloudy, 6 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 Jablonec nad Jizerou.