The increasingly annoying sequence of downpours and a mild-temperature outlook might constitute the imperfect storm for the annual fall-foliage show around here, an expert says, and the early signs aren't encouraging.

"Normally by the end of September you start to see some signs of coloration," said Marc Abrams, a forest ecology professor at Penn State who has been monitoring autumn colors for three decades.

"And I've seen very little coloration."

One factor has been the rain. Rainfall has been radically above normal for the last two months throughout  Central and Eastern Pennsylvania and New Jersey, according to the Middle Atlantic River Forecast Center. In some counties, it has been double the long-term averages, approaching 20 inches.

It also has been warm, and the government's Climate Prediction Center sees odds strongly favoring above-normal temperatures for the next two weeks throughout the Eastern foliage zones. They also favor above-average rains.

So what might that mean for what the late naturalist Edwin Way Teale eloquently described as "the glorious, flaming sunset of the year?"

"This is the opposite of what is needed to bring out the best and timely colors," Abrams said. His ideal formula would include  adequate but not excessive rain during the growing season, and "a nice cool-down in late September through mid-October."

Those conditions are ideal for allowing nature to orchestrate its magic. Responding to autumn's light cues, chlorophyll in deciduous trees recedes and gives way to yellows and oranges. Food-bearing veins at the leaf base shut off, the stranded sugars manufacture the show-stealing anthocyanins that turn leaves aflame.

Predicting how brilliant fall will be in any given woods, or any given species, is impossible, but Abrams said it might be a good year to head for the hills of upstate New York, Vermont, and New Hampshire.

Don't give up on fall around here. Abrams pointed out that nature is notorious for executing the counter-intuitive, doing exactly what you don't expect.

Also, and sources indicate this has happened before, the atmosphere might well disobey the forecasts.

In any event, we've never known autumn to be a complete bust in the Philadelphia region, where the peak typically occurs in the last week of October. We've never seen it pass without at least some splashes of scarlet, gold, and cinnamon.