Traditionally, the bulk of the leafy transformation begins in the western parts of the state by the third week of September and gradually spreads south and east through October. State foresters expect the change will occur within that general time frame this year, though weather conditions could slightly alter it. In Western Maryland, peak viewing conditions are expected around the second week of October. Leaves in Southern Maryland and on the Eastern Shore should peak later in October and into November. The bright colors become visible in the fall as plants begin to shut down for the winter and slow their production of chlorophyll.
Chlorophyll produces the bright green pigment that colors leaves throughout the spring and summer.
During the spring and summer months, the green pigment masks the red, yellow, and orange pigments also present in leaves. As chlorophyll production ceases, the green disappears and the other pigments become visible, according to state foresters. Weather plays a large role in determining the brilliance of the colored leaves and the length of time they hang on the trees before dying. Foresters point to three criteria required for optimum viewing conditions. First, the trees must enter the fall healthy, which the abundance of precipitation this year 29 inches at Baltimore-Washington International Airport through July, over 20 percent higher than normal has ensured.