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New Englanders eager to see the region’s iconic fall foliage in the coming month should hope for little rain and cool nights over the course of the next few weeks, one researcher says.

Heidi Asbjornsen, an associate professor of ecosystem ecology at the University of New Hampshire, said she’s optimistic about a favorable fall foliage season, given the weather conditions of the current growing season and the meteorological predictions for the time leading up to the fall.

“This has been a relatively good year overall, as far as growing conditions,” Asbjornsen said. “We’ve had sufficient moisture for the most part, and we haven’t had any major pest outbreaks that would cause a lot of leaves to drop early.”

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Dry, sunny days and cool nights are ideal for prime foliage in the fall, but these conditions must come in moderation, Asbjornsen said. The weather conditions over the course of the next few weeks are critical to the duration and intensity of the foliage New Englanders will see in October and early November.

Weather researchers at NOAA expect El Niño, a climate phenomenon that occurs every three to seven years, to bring warmer-than-normal temperatures to the United States through the winter, Asbjornsen said. This is good for foliage fans, as long as good sunshine, low precipitation, and cool nights persist.

Those ideal conditions would provide extended time for leaves to produce anthocyanins — the pigments responsible for the orange and red colors that have become a trademark of autumn in the Northeast.

“Although dry, sunny days would be favorable for the pigments to be produced, we don’t want them too warm, and we need temperatures at night that are cool enough,” Asbjornsen said.

If nights stay too warm as fall approaches, the chlorophyll in the leaves — the pigment that makes them green — will override the anthocyanins. For prime foliage, there should be no frost buildup at night during the early days of fall, and the temperature during the day should reach no more than 65 degrees, Asbjornsen said.

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And while dry days are good for impressive foliage, drought can be counterproductive. Extended periods without rain can make leaves more stressed, which facilitates the formation of an abscission layer in them that causes them to shed, Asbjornsen said.

So far, weather conditions have given foliage fanatics a reason to look forward to the fall, but only time will tell whether those conditions will last long enough to really make a difference this year.


Andres Picon can be reached at andres.picon@globe.com. Follow him on Twitter at @andpicon.