Warm, wet weather is predicted to continue through the rest of September and most of October in the mid-Atlantic, Northeast and Great Lakes regions, and those soggy conditions likely will result in a subdued foliage display, according to a Penn State forest expert.
“This is the opposite of what is needed to bring out the best and timely colors, which require cool and dry conditions with the onset of fall,” said Marc Abrams, a professor of forest ecology and physiology at the College of Agricultural Sciences. “I predict that there will be a late –– and muted –– leaf coloration this October.”
The Department of Conservation & Natural Resources’ Cecile Stelter, a district forester in Warren, explained how the weather affects pigmentation in leaves.
“Weather does affect the fall foliage process but it is only one component of a complex process that even scientists don’t understand completely,” Stelter explained. “Leaves change color in the fall due to a set of conditions including leaf pigments, sunlight, moisture, chemicals, tree hormones, temperature, length of day, site and genetic traits of individual trees –– just to name a few.”
Abrams noted that the foliage outlook is a bit better for the Great Lakes and Adirondack regions because –– although they received above-average amounts of precipitation –– they were spared the exceptionally high amount of rainfall that other regions received.
“I’m not expecting a total washout because even during the worst of times trees produce good-to-fair color,” he said. “But it may take a bit more hunting to find the best color this year. What we need now, and what we are not likely to get this fall, is for cool to cold temperatures to arrive by early to mid-October to bring out the best colors.”
For three decades, Abrams has studied how seasonal precipitation and temperature influence timing and intensity of fall colors in central Pennsylvania.
“We believe that clear, bright days, low but not freezing temperatures, and dry but not drought conditions promote the best fall colors,” he said.
Stelter echoed Abrams by adding, “The best weather conditions to favor a colorful fall foliage season are: warm, sunny days followed by cool nights with temperatures below 45 degrees but not freezing. Rainy or cloudy days without much light occurring near the peak coloration time can decrease the intensity of the fall colors, as will an early hard frost.
“We know that as the days begin to shorten in daylight, trees react by producing less chlorophyll (the green pigment that makes leaves appear green to us),” said Stelter.
“Since the leaves are not replenishing the chlorophyll then the green of the leaves begins to be replaced by the pigments of other colors which is why we start to see the other colors of yellow, red, yellow, etc. The reds, purples, etc., come from pigment in the cells called anthocyanins. The yellows, browns, oranges, etc., come from pigment in the cells called carotenoids.”
Abrams reflected on his over-three decades of gauging fall foliage by stating he is most impressed by “the resiliency of the display.”
“Year after year, despite the conditions, there are places where the trees show good color, but perhaps not great color every year,” Abrams said.
