April in Sioux City is the rainiest month of the year. In April, the weather in Sioux City is typically warm. Average daily high temperature in April is about 14 degrees above zero. On average, Sioux City has 11 rainy, 10 partly cloudy, 8 sunny, and 1 cloudy day in April. The rains are usually heavy. April as well as February, March, November, and December is considered the most uncomfortable time to visit Sioux City.