Weather will likely play an important role when you plan your trip to Decatur, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually July and June with an average temp of 73°F, while the coldest months are January and February with an average of 33°F. The snowiest months in Decatur are February, April, March, and January, with each month seeing an average of 5 inches of snowfall.