In Syracuse and elsewhere, temperatures have begun to dip into the mid-50s (in degrees Fahrenheit) some nights, a sign of cooler temperatures ahead, Leopold told OurAmazingPlanet. Colder temperatures and shortening days serve as signals to plants to begin reducing the amount of chlorophyll produced and to start preparations for winter, which involves moving sugar and nutrients from leaves to roots.
Sufficiently cool temperatures can also directly reduce the amount of chlorophyll produced. Without being continuously renewed, chlorophyll breaks down and eventually leaves will fade from green to yellow or red.
Ideal conditions for development of fall colors include sunny, warm days and cool nights.
Also potentially affecting the fall colors is the little rainfall that has occurred in the area this year, Leopold said.
Some trees are already showing color due to stress, Leopold said. When a tree doesn't get enough water or is otherwise harassed, it may quit producing chlorophyll earlier, allowing colors to show. This strategy allows it to prevent itself from losing water and to wait out the winter.