In August, the weather in Janske Lazne is typically warm. Average daily high temperature in August is about 20 degrees above zero. On average, Janske Lazne has 17 rainy, 9 partly cloudy, 3 sunny, and 2 cloudy days in August. The rains are usually heavy. August as well as February, March, April, and May is considered the most uncomfortable time to visit Janske Lazne.