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Fall foliage in the Philly area may suffer from the unusually warm and wet weather

With overnight warmth, the annual foliage show appears to be off to a slower-than-usual start. But don't give up on the season yet.

Fall foliage at the Morris Arboretum of the University of Pennsylvania last November. Our turn is coming, but it might be a little later than usual.
Fall foliage at the Morris Arboretum of the University of Pennsylvania last November. Our turn is coming, but it might be a little later than usual.Read moreMONICA HERNDON / Staff Photographer

The next several days should be ideal for morning walks in the Philly region with temperatures in the low 60s, a solid 10 degrees above long-term normals.

But what’s good for the walkers — and at least tolerable for the Broad Street runners on Sunday — isn’t necessarily good for the annual fall foliage show.

On the eve of a peak fall-tourism weekend, as the colors ripple southward, they appear to be encountering a few roadblocks with unusually warm weather blanketing the entire Northeast.

While the season has time to rebound, “it is not looking good right now, sorry to say,” Marc Abrams, a Penn State professor of forest ecology and physiology, said Thursday.

Cooler weather is an essential cue for the leaves to stop producing the green chlorophyll that masks the reds, russets, oranges, and yellows, said Abrams, who has been monitoring foliage seasons for 40 years.

» READ MORE: How to track progress on Pa.’s fall foliage

“This unusually warm and wet fall appears to be really hurting fall colors this year,” agreed the Pennsylvania Department of Conservation and Natural Resources in its weekly report posted Thursday. The agency advised weekend leaf-peepers to head north of I-80, which cuts across the state from East Stroudsburg to the Ohio border.

Farther north, peak color is reported in Vermont’s Northeast Kingdom and in central parts of that state, but the New England color also “seems to be delayed,” said Stephanie Spera, a University of Richmond researcher who is studying fall foliage trends in Maine’s Acadia National Park.

» READ MORE: Fall is getting warmer in Philly. Here’s what that means for trees, ticks, and birds.

Most of New England is “seven to 10 days” behind, said Jim Salge, a meteorologist who is the foliage forecaster for Yankee Magazine, in Dublin, N.H.

Overnight lows several degrees above normal are expected during the next several days in the Boston area, and perhaps 10 or more above average in Burlington, Vt., as a dome of warming high pressure dominates the upper atmosphere in the East.

While autumn temperatures in the Northeast have been above the 20th-century average every year since 1998 — and last year were 2.7 degrees Fahrenheit above — according to the National Centers for Environmental Information, the forecast for the next several days would far exceed that trend.

And as frequently happens, while it’s warm here, a major cooldown is expected in the West, likely persisting for the next two weeks.

It is not clear when the pattern might flip, but the government’s Climate Prediction Center has the odds strongly favoring above-normal temperatures in the Northeast through the same period.

» READ MORE: Five fall hikes near and far from Philadelphia

“I expect that will delay and somewhat diminish fall colors,” said Abrams.

But he also advises against giving up on the show.

Through the years, the foliage has shown a certain “resiliency,” and despite adverse conditions the leaves have produced “good color” at the very least, he said. “But we need the weather now to cooperate and cool down.”