September weather will determine brilliance of fall leaves

September weather will determine brilliance of fall leaves
A line of colorful maples stands outside the Old Cranberry School in Avery County, N.C., while windswept leaves create patterns along the ground. (Photo by Skip Sickler)

CULLOWHEE, N.C. — Hotels and retailers are gearing up for the fall foliage season in the North Carolina mountains, but the brilliance of the show from the changing leaves is still to be determined.

The key to almost every season is the temperatures and amount of sunshine in September, Appalachian State University professor plant eco-physiology Howard Neufeld said.

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"Fall colors are very dependent on the weather. September is the most crucial month. If we start to get a cool down, with sunny days and cool nights, those are the best conditions for fall color," Neufeld told the Citizen-Times of Asheville.

<span>Fog meets bog in this photo shot in Linville Gap, just down the road from Grandfather Mountain. As cooler temperatures persist, with leaves following suit, Grandfather&rsquo;s naturalists posit that autumn 2015 seems to have started a week earlier than anticipated. To follow this year's fall color, check out Grandfather Mountain's Fall Color Gallery, updated daily at <a href="http://www.grandfather.com">www.grandfather.com</a>. Photo by Skip Sickler | Grandfather Mountain Stewardship Foundation <!--[if !supportLineBreakNewLine]--> <!--[endif]--></span>
Fog meets bog in this photo shot in Linville Gap, just down the road from Grandfather Mountain. As cooler temperatures persist, with leaves following suit, Grandfather’s naturalists posit that autumn 2015 seems to have started a week earlier than anticipated. To follow this year's fall color, check out Grandfather Mountain's Fall Color Gallery, updated daily at www.grandfather.com. Photo by Skip Sickler | Grandfather Mountain Stewardship Foundation

The fall tourism season is crucial to western North Carolina. Officials estimate it brings up to $800 million to the state.

And it lasts a long time, thanks to elevations from the eastern United States highest peak, Mount Mitchell, at 6,684 feet to areas in the Piedmont closer to 1,000 feet above sea level.

"One of the benefits of looking at color in WNC, we have such a tremendous elevational difference. It's the longest fall color period in the United States. In New England, being farther north and less elevational change, at most it's two weeks. If you miss it at one elevation for some reason, then just go down to a lower elevation and you'll see it the following week," Neufeld said.

Colors in the highest elevations will peak in September, while the lower elevations will see their most vibrant color in early November.

And that September sunshine is also critical to the vibrancy of colors. Plants produce anthocyanins -- the same red pigment that colors strawberries and roses - in the early fall if they get enough sunlight for photosynthesis, Neufeld said.

"That's why if it's cloudy and rainy in September and the plants get less light, you don't get as bright red color," he said.

There is one very critical wild card to any fall foliage season in the North Carolina mountains, and that happens hundreds of miles away. A dying hurricane can bring heavy winds and rain into the mountains, stripping leaves and ending the foliage season in one bad day or two.

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