Jennifer Adams, 10, staring at the deep, white pile of feathers on a large snowy owl at the Audubon Naturalist Society regional headquarters in Bethesda yesterday, asked her mother if the wide-eyed Arctic bird was thick with feathers because it was getting cold.

Jennifer's mother bent down and said no, the owl always has loads of feathers but it may get even more when the temperature drops.

If Jennifer's mother is right, the snowy owl should sprout more feathers tonight. Temperatures are expected to drop into the low to mid-30s, bringing the first frost of the autumn season to the city, according to National Weather Service. Daytime temperatures today will peak in the high 50s or low 60s as brisk breezes, sweeping autumn leaves through Washington's streets with gusts of up to 25 miles per hour, make today noticably cooler than the Indian summer 80s of last week.

Yesterday, morning showers gave way to the beginning of a golden autumn weekend in Washington, inviting the area's residents to a multitude of seasonal outdoor activities.

At the Audubon Society it was the first day of the two-day All About Owls Festival, with a selection of caged owls on display. "We have the owls here," said Tom Gause, regional vice president of the society, "because October is the beginning of their hooting back and forth, the courtship ritual. Come January and February, they'll mate and by March the young are hatched and beginning to go out of the nest."

The society arranged for a commemorative U.S. Postal Service postmark for a new series of Wildlife Conservation-USA stamps featuring several types of owls. The postmark used to cancel the stamps celebrates the "Audubon Naturalist Society; 80 years of Wise Conservation."

Yesterday also was the day for the annual Harvest Festival at the Shiloh Baptist Church, at 1500 9th St. NW. Marching bands from Woodson and Dunbar high schools celebrated the occasion by parading up Rhode Island Avenue and returning to the church where a carnival, food fair and free health care clinic were held.

"The purpose of the festival is to bring the church and the community together," said festival chairman Mary Hendrick. "This time of year people have come back from vacations and are getting into activities. We want them to know we are here."

A blast of cold wind, carrying a short flurry of rain blew into the crowd of band members, Boy Scouts and children nibbling on cotton candy and candied apples. "I had scheduled it for later in October and moved it up," Hendrick said. "But this is too cold. Next year I'll have to move it up to September."

As sunlight broke through the cloudy sky later in the afternoon, the semiannual White House Garden Tour began.

"I've toured the White House before but never the grounds," said Linda Taylor of Alexandria, as she stood in the Children's Garden with her family, including her mother-in-law who is visiting from Canada. "I wanted to see what was out here . . . nothing really surprises me but it is startling to see how immaculately they trim the shrubs and the perfection of the flower beds, the trees and the lawn."

Tanya Gibson, of Washington, was shivering as she stood beneath the South Portico listening to the Marine Band. "I stayed in bed all morning," she said. "I love to sleep when it is cloudy and cold. But I didn't really think it was this cold. My gosh, I'm wearing a coat. I had a jacket on when I came out and I went back in and got the coat."

The tour of White House gardens and grounds will be open again today from 2 p.m. to 5 p.m. In addition to viewing the Jacqueline Kennedy Garden, the South Lawn, the Rose Garden and the Children's Garden, visitors will be able to tour the first floor of the White House.

On the sidewalk outside the White House, Tom Cahill, wearing green and white striped shorts, limped home with a twisted knee from the first annual Washingtonian Minithon, sponsored by Washington Magazine.

"When the weather is cool like this it takes me longer to warm up," said Cahill, who ran with many others in the race on National Jogging Day. "I hurt my knee running last week," Cahill said as he hobbled past the line of tourists waiting for a White House tour, "And I really shouldn't have run today, but it would have been hurting me a lot more now if I hadn't gotten out of bed to run today."

Throughout the city, the bright orange and golden color of pumpkins, bottles of cider and turning leaves proclaimed autumn. "In the last week it has been warm like summer, cool like spring and chilly like the fall," said James Elliott, as he stood in Lafayette Square Park. "It's kind of ominous. The one season that's missing is winter. But you know that's coming."