The timing is also temperature dependent. I live in the agricultural area just outside of town. It's warmer in town than by my house. The trees in town (and in the city 50 miles away) are always reaching their peak fall colouration a week later than by my house (and the rest of the countryside). A hundred miles to the south from where I am and again the trees turn colour later than by my house.

It has been a really warm fall, very summer-like until about a week ago. That has delayed the fall colours by about two to three weeks. Normally I'd expect peak colouration to happen here in the last week of September.

The year of the drought introduced a different factor into the equation: stress. I suspect drought stress pushed the onset of fall colouration earlier that year.