While Labor Day and professional football mark the unofficial start of fall for many people, an even more traditional sign still heralds its beginning for others the coloring and descent of leaves that lends the season its name.
The bright hues have indeed begun to pop from trees across the river valley. Some residents may have noticed, however, that a few trees seemed to skip the sunny yellows and fiery reds entirely, with leaves that instead turned a crispy brown and fell dead to the ground weeks ahead of schedule.
Could the exceptionally hot and dry conditions that we recently experienced play a role in this fall's foliage season?
The full range of tree coloration can be seen behind Grimm’s Bridge in Beaver Creek State Park, with some still wearing their full summertime greenery, while others are well into their transformation into the yellows, oranges and browns that will soon cover the hillsides. Note the ivy creeping along the stone wall at the base of the bridge already turned a bold red. (Photo by Richard Sberna)
"It's been an interesting summer," said John Darnley, a meteorologist from the Pittsburgh office of the National Weather Service in Moon Township, Pa. According to NWS readings, the summer began very hot and dry in June, with some rain tempering the heat in July before finally leveling off to more normal "dog day" conditions in August. "We've kind of been up and down," he said.
However, you have to go back to this past winter, which was also abnormally warm and led into a very early spring, to get the full story. "The leaves started to form up in some areas in early March," Darnley said. The earlier that the leaves appear, the earlier they could be expected to change color and drop from the trees, following their normal life cycle.
According to Darnley, most trees in our region have completed their year's growth by the end of June.
Carbohydrate storage during a tree's growth period plays a major role in determining the time its leaves begin to change color and eventually fall. "If it had a lack of water, that's going to affect the life cycle of the leaf," Darnley said.
The main factor is photosynthesis, which is dependent on adequate supplies of sunlight, carbon dioxide and water to create those critical carbohydrates. It is a lack of any of those factors that makes the difference rather than unusually warm or cool temperatures. "Fall colors appear at the same time each year, whether the temperature is cooler or warmer than normal," Darnley said.
What usually causes the brilliant colors of fall isn't so much the lower temperatures as the shorter days. Since the first day of autumn on Sept. 22, we've reached the tipping point, with more darkness than sunlight and the period of sunlight becoming shorter by approximately two minutes every day.
Temperature only comes into play this time of year in extreme cases, such as if a period of early snow or frost were to descend upon the area. "If we had several days of very cold weather, that would not be advantageous for a very colorful fall," Darnley said.
The additional factor of recent blustery thunderstorms in the valley have only hastened the leaves' early exit from their trees, Darnley added. "You get a little bit of a wind on top of that, and the leaves will separate much faster, especially as they start to dry out."
So while this year's foliage season could be shorter than normal, at least the conditions in which to get out and view it should be nice. Darnley said that weather models from the National Climate Prediction Center call for above-normal temperatures and below-normal precipitation in the Ohio River Valley for the month of October.