The small styrofoam box was lofted into the hot morning sky beneath a hydrogen balloon, bound with its instruments from a parched Virginia field to the upper reaches of the troposphere.

As it rose, a tiny blue antenna that looked like a fuse began to beam back data on air temperature, pressure, humidity and wind speed--clues, perhaps, to that elusive commodity: rain.

But high above the National Weather Service station whence it came, where in summers past, thunderstorms might rage, the small box would traverse only hot, stagnant, fearsomely stable air on this day.

And nary a drop of water.

There might be drops today, though. The Weather Service says there is a 50 percent chance of rain as a front moves in from the Carolinas.

But more often lately, the local atmosphere--traditionally a reliable source of summer precipitation--has been just as it was on the day the styrofoam box went aloft: too warm and still, with too little of the aerial turmoil required to breed thunderstorms, experts say.

And up until this week, it's been quiet in the two distant places that usually can be counted on to provide whatever moisture local summer storms don't: the Atlantic Ocean and the Gulf of Mexico, whence come hurricanes and tropical storms whose remnants douse the Washington area.

Two tropical depressions--one near the Cape Verde Islands off Mauritania, one off Vera Cruz, Mexico--have, finally, developed in recent days and commenced inching toward the United States, but forecasters said yesterday it's far too early to think of either depression as likely salvation for the brown lawns of Washington.

"The one in the gulf seems almost impossible that it would affect the Washington area," said Richard Pasch, a hurricane specialist with the National Hurricane Center. "But the one in the Atlantic is coming from the place where storms traditionally come from during the season."

Even so, Pasch said, "it's way too far off to tell where it's going. At this point, it's as likely to threaten the Washington, D.C., area as it is Brownsville, Texas."

Vernon E. Kousky, a research meteorologist with the National Oceanic and Atmospheric Administration's climate prediction center in Camp Springs, said that attributing a prolonged lack of meaningful rainfall to any one cause "gets very complex." Lately, he said, almost everything seems to be "anti- precipitation."

Kousky said one of the summer's usual providers of rain is the old standby afternoon thunderstorm, brewed by a day of hot muggy air that rises into the cooler reaches and then cooks off with a gusty downpour.

This year, it's just not happening.

"It's not happening because the air is so stable," he said. "It's so warm aloft that it's just capping everything and won't allow those clouds to build up.

"You want instability," he said. "The cumulus clouds that form into thunderstorms around here need instability. It requires warming at the surface, but cooling aloft."

Instead, the upper air has been hot and compressed and has tended to settle into a thick blanket that blocks the kind of atmospheric fireworks that bring on rain.

There have been tantalizing moments.

"We scratch our heads," said John Newkirk, who oversees local balloon operations at the Weather Service's complex in Sterling. "Sometimes you have these fronts coming through. The temperature's in the 90s. You got dew points in the 60s. And you don't get anything."

Things are subdued elsewhere, too--though the jet stream, another element gone missing for the summer, made a rare southern appearance, sparking showers over the weekend. Off the bulging coast of west Africa, where tropical weather normally grows this time of year, weather satellites 20,000 miles in space have seen little in the way of a possible big storm until recently, even though forecasters have been predicting a busier than usual hurricane season from the region.

There still is hope, however. Kousky said the peak hurricane season just began last week, and the season doesn't peak until about Sept. 10.

Such is the extent of the local drought that forecasters say a dose of often-dangerous tropical weather would be a godsend.

"That would certainly go a long way to put this drought to bed, on a short-term basis, anyway," Jim Travers, the meteorologist in charge at the Weather Service station in Sterling, said last week. "Anything short of that, it is not looking real promising."

There were actual hurricanes afoot last week, Dora and Eugene. But they were fitfully wandering the eastern Pacific off South America, miles from land and headed for cold water far out to sea.

Locally, forecasters said, things could get even worse.

"Once we get out of the summer," Kousky said, "generally speaking, September into early October is one of the drier times of our year. So things don't look very promising. It's very hard to break a drought at that time of year.

"Unless we get a tropical system--which is one of our hopes--probably the drought will continue into the fall," he said. "It could very well get into the winter.

"And if we don't replenish . . . with ample rains next spring, we could be in serious problems again for the next growing season."

Staff writer Scott Wilson contributed to this report.