April in Ishim is the rainiest month of the year. In April, the weather in Ishim is typically cold. Average daily high temperature in April is about 5 degrees above zero. On average, Ishim has 17 rainy, 12 cloudy, and 1 sunny day in April. The rains are usually moderate. April as well as January, February, September, and October is considered the most uncomfortable time to visit Ishim.