The plunge in temperatures this past week could be good news for leaf peepers. In a week or so, foliage in popular areas of the Poconos, such as Jim Thorpe and the Lehigh Gorge, will likely reach its peak, according to a weekly report by foresters and a tourism official.

Foresters in Pennsylvania's Department of Conservation and Natural Resources are reporting that the drastic weather change from the first two abnormally warm weeks in October has spurred a major shift in foliage throughout the commonwealth.

Warmer weather had been tricking hardwood trees to keep producing chlorophyll, a chemical used for converting sunlight to energy that makes leaves appear green.  When chlorophyll retreats in cooler weather, other pigments emerge and leaf colors pop.

Also impacting the timing of peak leaf peeping this year: A fungus forced many hardwoods like red and sugar maple — those that produce some of the most vibrant colors — to drop their leaves early.  It's the second year in a row that foliage has been lessened by the anthracnose fungus, which causes leaves to shrivel and fall off before turning color. Sycamore, walnut, ash, and white oak were also impacted.

While the fungus brought bad news for trees in much of the state, the Poconos largely avoided the worst of the outbreak, said Jeff Woleslagle of the Department of Conservation and Natural Resources.

"The Poconos are one of the bright spots of the state right now," Woleslagle said. "They were not unaffected, but not affected to the degree that other areas of the state were."

Woleslagle said some parts of the Poconos should be peaking this weekend and through next week.

The Poconos are popular with leaf peepers, hikers, bikers, campers, and white-water rafters. About 2,400 square miles, the region is generally defined as Carbon, Monroe, Pike and southern Wayne Counties.

The region boasts nine state parks and recreation areas: Beltzville, Big Pocono, Gouldsboro, Hickory Run, Lehigh Gorge, Promised Land, Prompton, Tobyhanna, and Varden.  And it also includes the Delaware Water Gap National Recreation Area.

As of Friday, trees in the more northern counties, Monroe and Pike, had the most vibrant colors on display.  Indeed, staff at Delaware State Forest reported that Monroe County, as well as Pike, was at peak.

Lehigh Gorge State Park in Carbon County still might have a week or so to go before approaching peak — so, too, does the surrounding town of Jim Thorpe and nearby Mauch Chunk Lake Park, both in Carbon County.  Southern portions of the Poconos are still mostly green.

"Parts of the Poconos region are peaking," Woleslagle said. "And I would say definitely by next Saturday," Oct. 27.

Kelly Shannon, a spokeswoman for the Pocono Mountains Visitors Bureau, said the warm weather and storms definitely had an impact. The bureau offers its own foliage forecast.

"Unfortunately, with all the wind and rain we've gotten, it's not as vibrant and a little delayed," Shannon said.

Normally this week would be the peak in the central Poconos and next week would be the peak in the southern Poconos, she said.

"But in the next two weeks, the central and southern regions should start to peak," she said. "With the colder weather, by early next week we'll start to see a lot more change."