The region experienced an extraordinary week of weather last week, and for epicures of fall foliage pining for a coronavirus sanity break, the meteorological seasonings couldn’t have been better.

For all-out color, this should be “a vibrant peak season,” the Pennsylvania Department of Conservation and Natural Resources said Thursday in releasing its first 2020 foliage report.

Sequences of sunny days and cool nights from September into early October are ideal conditions for routing the chlorophyll and luring the latent scarlet, oranges, and yellow pigments out of the leaves, says forester Ryan Reed, the Pennsylvania report’s author, and other foliage experts.

That recipe was followed to near perfection around here from Sept. 19 through Wednesday. For the first time since the first week of June 2016 (yes, that was during the last presidential campaign), Philadelphia recorded five consecutive clear days. And officially, the city had four straight daily low temperatures in the 40s, which hasn’t happened in September in 35 years.

The government’s outlook through the first week in October favors below-normal temperatures. The dry run could end next week, but that could have the benign effect of extending the season, Reed noted in his report.

Some portions of key foliage-viewing areas in the East are in drought conditions, and while experts say dryness can accentuate color and is the mortal enemy of the color-killing leaf fungus anthracnose, it could also lead to earlier leaf fall and a shorter season.

The bane of autumn, the anthracnose fungus, can affect the autumn show. Here its effect is shown on a local tree.
Richard Ruch
The bane of autumn, the anthracnose fungus, can affect the autumn show. Here its effect is shown on a local tree.

In New England, where it has been exceptionally dry, the show has started, with the peak expected in the next 10 to 14 days, said Jim Saige, the foliage specialist for Yankee Magazine. “I expect it to be early and brief,” he said. Spotters in northern Vermont already were reporting “moderate” color as of Thursday.

Parts of the Northeast have been extremely dry, as shown in his map posted Thursday.
U.S. Drought Monitor
Parts of the Northeast have been extremely dry, as shown in his map posted Thursday.

The color wave already has lapped into the Keystone State, with blushes of red on the maple leaves, according to the Pennsylvania report. The peak in the north-central forecasts could come as soon as the week of Oct. 4.

For those who would prefer not to venture too far from home, the best guess for the peak in the Philadelphia region would be the last week in October, although foliage seasons are subject to the caprices of short-term weather.

Early frosts, for example, are leaf killers, and it is all but impossible to know precisely how trees ultimately will respond to spring and summer temperatures and rainfall. But short-term forecasting soon might well be possible.

Using satellite imagery, Xiaoyang Zhang, a researcher at South Dakota State University, said he had success with five-day coloration forecasts during a five-year pilot program funded by the National Oceanic and Atmospheric Administration. He said he hoped to have a forecast system operating in 2022, with backing from NASA as part of a larger vegetation study.

By then, let’s hope the coronavirus is as forgotten as the fallen leaves of 2020.

Here are some viewing suggestions for Pennsylvania and New Jersey.