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Environment & Science

When will fall foliage peak in the Lehigh Valley? Depends on September temperatures

Helfrich Springs Grist Mill for fall foliage story
Donna Fisher
For LehighValleyNews.com
Fall colors are in full display outside Helfrich Springs Grist Mill along Mickley Road in Whitehall Township in this file photo.

  • September temperatures could determine timing for this year's fall foliage
  • The Lehigh Valley is still a few weeks away from peak colors
  • An invasive insect could also impact foliage

BETHLEHEM, Pa. — The timing of this year’s peak fall foliage could depend on how the rest of this month shakes out, temperature-wise.

“If we have an abnormally warm September, then it’s going to be delayed,” said Ryan Reed, a program specialist with the Pennsylvania Department of Conservation and National Resources. “If it cools down really nicely — as you might expect, through history — then, you should expect it to be a pretty normal season in terms of timing.

“It’s a little too soon to tell, but I would say that’s a good baseline.”

Leaf-peeper season is right around the corner in the Lehigh Valley, moving from north to south as temperatures drop into fall across the region. The Valley generally peaks in mid-to-late October, with trees popping brilliant yellows, oranges and reds across the landscape, but the weather over the next few weeks could give clues to narrow down timing.

The peak could come a little early this year, said EPAWA meteorologist Bobby Martrich, starting the last full week of September, then gradually increasing in early October.

“I think we may reach peak or near peak foliage by mid-October this year, and past peak by October week four — and certainly by the end of the month.”
EPAWA meteorologist Bobby Martrich

“I think we may reach peak or near peak foliage by mid-October this year, and past peak by October week four — and certainly by the end of the month,” Martrich said.

From drought to deluge

Martrich’s leaf-peeping prognostication took into consideration weather patterns so far this year, including dry stretches and periods of rain.

“During the growing season, we had the early drought in May and early June, followed by the deluge and well above normal rainfall from mid-June through July, then generally near average since then,” Martrich said. “The cooler temperatures (overall) this summer should also factor into it.

“We had a cool June, near average July, and cooler August. But now in September we project it will be +1.0°F to +3.0°F and slightly above average when taking a mean of the 30-day period.”

A drought was declared for the Valley and for most of the rest of the commonwealth in early June, following the region’s second-driest May ever, behind only the 0.09 inches recorded in May 1964.

In July, the U.S. Drought Monitor showed the entirety of Northampton County as “none” for drought status, as well as the majority of Lehigh County, after soaking rains moved through the area. As of Monday, the state’s Department of Environmental Protection still lists both counties in a “drought watch.”

Drought Watch
Pennsylvania Department of Environmental Protection
As of Tuesday, both Lehigh and Northampton counties were included in a "drought watch," according to the state Department of Environmental Protection.

“That did not bode well for a good season,” Reed said of the dry weather in May. “It just seemed like our trees weren’t getting the head start that they needed.

“And then the spigot turned on in June and July, and most of the state got a reasonable amount of rainfall to get our trees going, and to get them well-nourished before fall foliage season.”

Parallel to drought considerations, the Valley this year dealt with a new environmental threat: wildfire smoke, blown into the region from Canada. (Those fires are still burning. As of Monday, there were 925 active fires, with 560 of those deemed “out of control,” according to the Canadian Interagency Forest Fire Centre.)

In early June, the region had a rash of days with some of the worst air quality ever recorded attributed to the smoke. As the hazy air lingered, stuck in the trough between South Mountain and Blue Mountain, residents struggled to breathe and air purifiers were in short supply.

The smoke returned in mid-July, though not as severely. While the smoke’s impacts on the Valley’s plants, crops and water may be few due to the short duration of smoky days, experts said it’s a largely understudied topic.

Both Martrich and Reed said they didn’t think the smoky days the region saw over the summer would impact fall foliage.

“I really don’t expect [the smoke] to have any effect on the leaf color this year,” Reed said. “If that continued over a long period of time, then, of course, you would expect that to affect photosynthesis because they would just be receiving less available sunlight due to the smoke.

“But trees are pretty resilient to that sort of thing.”

As the summer progressed, temperatures trended lower than normal. The Valley did not see a single 90-degree day in the month of August — the warmest day reached 87 degrees – and the month ended 2.3 degrees below the monthly average.

In contrast, it seemed like Mother Nature cranked the thermostat so far in September, already averaging 4.4 degrees above normal temperatures.

‘We’re in good shape’

His seventh year forecasting fall foliage for the state, Reed said he’d rather it be a little too dry than too wet. The 2017 and 2018 seasons were marked by rain, and produced “lackluster” foliage due to anthracnose leaf blight, a disease that thrives in prolonged wet weather.

“Overall, I’d say, statewide, we’re in good shape for a beautiful fall foliage season.”
Ryan Reed, program specialist with the Pennsylvania Department of Conservation and National Resources

“I think that we’re a good spot leading into the season,” Reed said. “Overall, I’d say, statewide, we’re in good shape for a beautiful fall foliage season.”

But the weather isn’t the only variable – this year’s foliage could be impacted by an outbreak of spongy moths, an invasive insect responsible for killing millions of oak and other tree species.

“They favor oak trees, and so they were defoliated to an extent,” he said. “Many of those trees put a new set of leaves on — they’ll probably be smaller throughout the state, I would expect, but nonetheless, they should exhibit some good fall color still, just because you still have a nice leaf canopy.”

Pennsylvania Weekly Fall Foliage Report 2022
Pennsylvania Department of Conservation and Natural Resources
The state Department of Conservation and Natural Resources posts weekly fall foliage reports starting at the end of this month. This report is from the first week of the 2022 fall foliage season.

Forest health is always a point of consideration, Reed said, and fall foliage is part of that.

“The fall foliage show, so to speak, that we get every year in Pennsylvania is kind of like our grand finale of our forest, trying to show us their importance,” Reed said. “ … I think people shouldn’t lose sight, during the rest of the year, of the benefits that our forests provide, in terms of the clean air and clean water benefits and habitat for wildlife and beautiful places to go.”

For those interested in planning a trip to see the leaves, Reed, through the state Department of Conservation and Natural Resources, posts weekly fall foliage reports starting at the end of this month. Last year’s are still available, and can give residents and visitors a preview of what this year’s timing could be.

For those farther north, there’s also the Poconos Fall Foliage Forecast.