John Lauterbach knows when the heat is really bad -- his snapdragons turn brown, the Peruvian lilies shrivel and the red carnations turn black.

Lauterbach, 45, has been selling bouquets of flowers at 15th and M streets NW for 14 years. This week, with four days of 90-degree-plus temperatures, business has been poor.

"The flowers wilt and I have to throw them away. And the customers, they wilt too. They just walk by and don't even look at my flowers," he said as he piled bunches of dead and dying flowers into a wagon for discard.

It will be just as bad through Saturday, according to Charlie Chilton, forecaster for the National Weather Service. "It will stay about 90 degrees," he said yesterday. "There's a weak front coming this way which may cause thunderstorms to become more numerous on Friday and Saturday."

And the foul air is still with us as well. The Council of Governments made it official at 4:30 p.m. when environmental planner Rob Kaufmann announced that yesterday was the fourth straight day of unhealthy air and the third day of a health advisory for the metropolitan area.

"A health advisory is issued when two of our reporting stations report over the standard of 100 for ozone and when we have a stagnant air mass," said Kaufmann. "That means that people with extreme heart and lung conditions and severe allergies should stay indoors."

One man who wished he had stayed in his air-conditioned apartment near Logan Circle was Howard F. Bolden. He sported a gray towel under his blue-brimmed hat as he waited impatiently for a friend to show up at 14th and P Streets NW.

"I keep my air conditioning set to the max. It's about 65 degrees in there. When you come outside you can feel the heat. It about knocks you over," he said as he paced the sidewalk.

Bolden, an unemployed construction worker, says he's wise to the city heat. "I've had 32 years experience with Washington heat. . . . Air conditioning is the answer."

At 5 p.m., Lauterbach was totaling up the damage to his flowers. "Today I lost money. I only had 14 customers so far. But I will be back Friday. I have to be, that's my best day of the week. I'll just keep my flowers in the shade and say a prayer that the Lord will protect them."