There is no formula to predict fall color. The intensity and peak time of color are determined by complex environmental factors and the genetic makeup of the plants themselves. For example, trees and shrubs of European origin evolved where the growing season is longer and cooler, so they stay green into the fall.
Ed, the “Color Scout” at Morton Arboretum
The “best” fall color for an area occurs during the shortening days of autumn when days are bright, sunny and cool, when nights are cool but not below freezing, and when there has been ideal rainfall.
Here’s a photo I took November 3, 2007. I’ve always thought that most trees were bare by early November, but here they look like they’re about at peak.
And here’s one taken October 18, 2008. In this one, there’s still a lot of green.
I have to keep adjusting how I look at the seasons. My timing seems to be off.