With temperatures in the 90s and humidity rivaling the back room at a dry cleaner, there were signs yesterday that even in buttoned-down Washington, molting season had begun. Across the region, lawyers and tourists, dogs, cats and horses shed jackets and shirts, hair and fur, for relief from the steam.

By midday yesterday, the National Weather Service issued a heat advisory for the region, effective through tomorrow, with a heat index of over 100 degrees. The index, a calculation of heat and humidity that -- much like the windchill factor in winter -- is a measure of what the weather actually feels like, puts Washington this week on par with the tropics, said Alex Sosnowski, an Accu-Weather meteorologist. Except, he said, "true tropical air is generally fairly clean."

Like the old saw says, it's not the heat but the humidity that's most dangerous. With the air so moist, sweat doesn't evaporate well, which limits the body's ability to cool itself.

"Our bodies regulate themselves within certain finely held parameters," said Gigi El-Bayoumi, an associate professor of medicine at George Washington University Hospital. That is helped or hindered by clothing, hydration and activity.

Loose-fitting clothes in light colors and fabrics are best because they don't absorb as much heat on steamy days. "Cotton allows breathability. Spandex doesn't," El-Bayoumi said.

Then again, less of both works, too.

Anna Nichols, a consultant who lives in Adams Morgan in Northwest Washington, said her usual attire slips a few notches when the weather gets like this. Nichols, 41, was wearing a spaghetti-strap top as she left a grocery store, an article of clothing "I usually only wear under a blazer," she said.

However, Nichols added, "I think there's only so much of the usual Washington propriety you can expect when it gets this hot."

In the dog-grooming trade, shave-down season is at its peak.

"I wouldn't want to wear a fur coat in the summer," said Pattie Dunne, 25, a groomer at Bay Hills Animal Hospital in Arnold, mowing the Alpine coat of a bouvier des Flandres into a doggie do better suited for a mid-Atlantic July.

Dunne said shaving a dog in summer reduces shedding and helps control skin allergies. She charges from $35 for a small dog to $70 for trimming one particular dirty, cranky chow chow. Hazards of the job include bites and scratches -- and cats, which hate close shaves as much as they do baths.

"This cat sent me to the hospital one time," she said, passing a big-gutted, buzz-cut 18-pounder.

No matter how torrid, summer is fleeting. So the heat didn't keep dozens of golfers from the midday discount at Jefferson Regional Golf Course near Falls Church yesterday.

About 2 p.m., as the heat index broached 100, Leo Brett, 17, watched two other McLean High School students putt into the final hole. Wiping their foreheads with their T-shirts, they headed for a pool. "The heat definitely made it more challenging," said Brett, sweat soaking the ends of his hair.

At the Bayberry Riding Center in Spotsylvania, 50 children and adults wore weather-inappropriate leather boots, knit breeches, long-sleeved shirts and black velvet caps for a horse show Sunday. Judges let riders shed their jackets, said assistant director Cat Isham. The horses had long since lost their winter coats.

By yesterday, hour-long lessons were cut to 45 minutes, and 20 riders were in short sleeves. Any chance of shorts?

"If you have ever had horse hair and slimy horse sweat on you, you don't really want to do that again," Isham said.

Howard County Police Capt. Merritt Bender peeled off his shirt yesterday -- but only to check the fiber content. "Sixty-five percent polyester and 35 percent rayon, [but] it's actually cool and comfortable," he said.

Like most police officers, Howard's 370 men and women in blue have little leeway on summer dress. After April 15, the force trades long sleeves for short and ditches the neckties. That's it.

Another sticky issue is the color of the shirts -- light blue -- bad news on a sweaty day. " 'Worry' is probably the wrong word to use" about that, Bender said; pitting out one's shirt is part of the job.

The Rev. Ron Potts, pastor at Mother Seton Parish in Germantown, said doing the Lord's work in a black, polyester blend clerical shirt with snap-in plastic collar is "part of the sacrifice." While some priests wear street clothing and a few monks get away with shorts under their long robes, most clergy still don the black pants, shirt and stiff white collar Potts wears.

"I don't complain too much," he said. Off duty, he wears clothes of his own choosing. "There is no clerical-issue bathing suit," he said.

By tonight, the air might dry out somewhat, Accu-Weather's Sosnowski said, "but humidity levels will creep back up Thursday and Friday." The weekend is expected to bring some relief. Until then, Sosnowski advised the region to follow his lead: "I have khaki pants on and a cotton shirt," he said. "I'm also in the air conditioning."

Staff writers Susan Levine, David A. Fahrenthold, Michelle Boorstein, Sandhya Somashekhar and Nelson Hernandez contributed to this report.

Myrle Moore, visiting from California, stretches out while granddaughter Jessica Tarmen sits quietly in the heat. Dejuan Souder, left, Cameron Clayton and Katelyn Mims play in the District.A couple of fawns keep cool by relaxing in the shade at Arlington National Cemetery. The air might dry out tonight, forecasters say, but humidity is expected to return and relief is not expected until the weekend.Griffen, left, and Flagler were taken to a Rockville PetSmart to have their coats shaved for comfort.