July in Derby is the warmest month of the year. In July, the weather in Derby is typically warm. Average daily high temperature in July is about 19 degrees above zero. On average, Derby has 19 rainy, 5 sunny, 4 partly cloudy, and 3 cloudy days in July. The rains are usually moderate. July as well as January, February, March, and June is considered the most uncomfortable time to visit Derby.