If you compare Waukegan with Naperville, which town has the higher percentage of warm days annually?
Naperville would be the clear winner in a comparison of warm days annually, but “warm” is a subjective term. A Chicago day on which the high temperature hits 70 degrees would be considered warm in January, but cool in July. Putting that consideration aside, the cooling effect of Lake Michigan, primarily in the spring and summer, is the single most important factor here. Waukegan sits right on the lake, whereas Naperville is about 30 miles from the lake. The cooling effect of a lake breeze sweeps across Waukegan frequently, and it’s chilling effect is strong, whereas that same breeze, even if it makes it as far inland as Naperville, is much weaker.