Our East Coast Autumn

If you feel that this fall has been marked by unusually spectacular fall foliage—the kinds of reds, golds, and oranges we associate with the Midwest and the East Coast—you're not imagining it. The University of Washington's Department of Atmospheric Sciences has noticed the atypically gorgeous colors as well, which have been a subject of chatter at its weekly weather meetings.

"It's the nicest fall I can remember, and I've been here 21 years," says Dale Durran, chair of the department.

The reason is this season's unusually dry and cloudless weather (which we had until the past week or so). The brightest foliage colors come when the nights are cool and the days are warm, explains atmospheric sciences professor Mark Stoelinga. This "diurnal effect" stimulates the chemical process that turns leaf color. Clouds, which we usually have plenty of this time of year, hamper this effect because they act like a blanket at night, stopping heat from radiating upward, and a barrier during the day, preventing the sun from permeating downward.

Dry weather is also conducive to the chemical changes that produce foliage color. Also, Stoelinga says, "Rain can knock the leaves off the trees and they make things more miserable generally so that you don't realize the colors. All you see are wet, rotting leaves on the ground." The early-season windstorms we typically have, though fewer this year, also steal the leaves from the trees.

Enjoy it while you can. No long-term atmospheric changes have taken place to ensure repeat performances. "You can't attribute this to global warming," Durran says. At least for now, though, the weather professors are staring out their windows toward leafy Portage Bay, soaking it all in.