With the first day of autumn just two weeks away, the question hovers in the air: When will the leaves start to change, and how colorful will they be this year?

It's a question not even the experts can answer with any accuracy.

"We did have a good year for color last year, and I'm not sure what the factors were to produce that," said Charles Bailey, senior forester with the Georgia Forestry Commission in Gainesville. "I was thinking it was going to be a poor year."

Certainly 2007 brought some tough challenges for North Georgia's trees. A late Easter freeze killed most of the new foliage, and the trees had to expend extra energy trying to regenerate. Then they struggled with severe drought, and last August a record heat wave caused temperatures to soar over 100 degrees almost every day for at least a week.

And yet, the trees came through with a brilliant finale. Instead of just turning brown and falling off, the leaves stayed on later than usual, and produced rich color.

"I've been here 26 years and I still can't predict what the leaves are going to do," said Tracy English, program assistant at Black Rock Mountain State Park in Rabun County. "Last year they didn't peak until the first week of November."

Why did this happen? Scott Merkle, professor of forestry at the University of Georgia, said despite the drought in 2007, there was just enough moisture to help leaves cling to the trees.

"Last year we got some rain at critical times, and had a decent fall even though it came late," he said.

This summer, temperatures have been cooler than normal. And though June and most of August were bone-dry, July was wetter than normal, and Tropical Storm Fay brought extremely heavy rain at the end of August.

What this means for fall foliage is anybody's guess. "There are a lot of theories on what the ideal conditions would be to produce the best leaf color," said Bailey.

He said a dry late summer seems to be better for orange and yellow pigments, while red and purple tend to dominate when there is late-season rain. But too much rain will dull the colors.
"And a hailstorm could just knock all the leaves off," he said.

The wild-card factor is tropical storms. If a hurricane brings gusty winds to North Georgia, it could strip the trees bare before they have a chance to produce any color.

That would be disappointing to the thousands of people who plan their fall vacations around leaf season in the Georgia mountains.

"People can book our cabins 11 months in advance, and they're all reserved for almost every day in October," said English at Black Rock Mountain, which is Georgia's highest state park and one of the best places for leaf-watching.

Black Rock Mountain has a live Webcam on its Web site so people who want to just come up for a day trip can check and see how the leaves are doing.

But visitors who booked cabins or campsites months in advance have no guarantee of seeing fall color when they arrive. They can only make an educated guess based on the historical record.

"The leaves really don't start to turn until the first frost," said English. "We usually dip into the 30s at night by the end of September, and the week after that you'll start seeing some color."

Mitch Cohen, information specialist with the Chattahoochee National Forest, said he expects to start getting phone calls about leaf color very soon. "For people in Florida, Alabama and south Georgia, this is the closest place for them to see fall foliage," he said.

Later this month, he said, foliage updates will start appearing on the forest's Web site. But since the national forest covers about 750,000 acres, different areas will experience autumn at different times.

"It varies so much with elevation," Cohen said. "You need a cold front with nighttime temperatures in the low 40s, upper 30s, with sunny afternoons. Generally we start seeing good color in the middle of October at the higher elevations, and it's all over usually by Nov. 10."

Cohen said the last two weeks of October offer the best opportunity to view foliage.

"We usually recommend the Richard B. Russell Scenic Highway (Ga. 348), or Ga. 180 from Brasstown to Suches," he said. "Everybody loves those scenes with the leaves reflecting on water, so Lake Winfield Scott (off Ga. 180) is an excellent choice."