Peak experience: Finally, foliage weather

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With this week's July-like intrusion, and temperatures averaging more than four degrees above normal since Sept. 1, the annual foliage show has shown a reluctance to pull back the curtain this season.

"My feeling is we're at least a week behind, maybe 10 days," said Jim Harbage, director of floriculture at Longwood Gardens.

But expect a major rally during the next several days.

The Pennsylvania Department of Forestry, which maintains a weekly briefing, says the peak period across southern Pennsylvania should begin right about now.

But Pennsylvania State University foliage expert Marc Abrams, who has been watching the show for over 30 years, said the recent warmth has slowed things down.

Warm sunny days and cool, frost-free nights promote the best color, he said, and while the region has had plenty of the former, it finally is getting the latter. Temperatures are expected to drop into the upper 30s by Wednesday morning.

In the macro sense, light trumps weather. In response to the more-oblique sun angles, chlorophyll in the trees recedes and gives way to yellows and oranges.

The food-bearing veins at the leaf base eventually close, and the stranded sugars manufacture the show-stealing anthocyanins that turn leaves aflame.

Weather, however, is a factor in the intensity and duration of the season. The experts say ample moisture in the spring is a key, and, fortunately, for all the recent dryness in the Northeast, the entire growing season was drought-free.

As for the effect of general worldwide warming, it remains unclear whether it is pushing back the onsets and peaks, but it evidently has been extending the color season, as first-frost dates have come later.

Abrams said the additional moisture associated with worldwide warming might adding splashes of additional color.

He said that the color he has seen is "better than I expected," and that state forestry folks say that in the northern tier, "the colors are wonderful right now."

Our turn in the Philadelphia area should be imminent.

In any event, we should remember that we are incredibly lucky to have autumn, and to be where we are this time of year.

Philadelphia is halfway between some of the most spectacular autumn destinations in the world, from the Blue Ridge Mountains of North Carolina to the White Mountains of New Hampshire.

And for the next 10 days to two weeks, we won't have to travel very far at all to savor what the late naturalist Edwin Way Teale described as "the glorious, flaming sunset of the year."