BOSTON — The searing temperatures and oppressive humidity that buckled bridges and knocked out power across the eastern US this week have now fallen to more tolerable levels.
Yet as cooler, drier air sweeps down into the East and summer monsoons begin to move up from the Gulf of California into the desert Southwest, forecasters are keeping their eyes on a longer-term problem gripping many areas affected by the heat wave - tenacious droughts, which this week's weather has done little to ease.
Arizona Gov. Jane Dee Hull has already declared a state of emergency, and Georgia has lost at least $700 million in crop damage in what farmers and forecasters there are calling "the drought of the century."
Indeed, the hot start to the East's summer comes at the end of a decade that has seen its share of weather and climate extremes - from record flooding on the Mississippi River in 1993 to high temperatures spawned in part by El Nio, making 1998 the warmest year on record. Parts or all of 35 states face droughts ranging from moderate to extreme, with little relief in sight. Regions of the Northeast, Mid-Atlantic, and Southeast are among the hardest hit, and thunderstorms that moved through the eastern US Tuesday evening merely teased wilting crops, sun-browned lawns, and shrinking reservoirs from Maine to Florida.
"We do see some relief on the horizon in the next week or two," says Robert Livezey, a senior research meteorologist with the National Oceanic and Atmospheric Administration's Climate Prediction Center in Washington. "But when you're in a drought with major deficits in precipitation, you need better-than-normal precipitation for awhile" to make up the deficit. At this point, he adds, forecasting models "give no clear signals one way or the other of drier or wetter conditions over the next few months."
Such ambiguity is of little comfort to Terry Wheeler, whose cattle ranch outside Globe, Ariz., falls within a "severe" zone on federal drought maps.
His rain gauges have collected not quite three inches of precipitation since November, less than half of what's normal - a disaster for the grass that helps feed his livestock. "Our springs are drying up," he says. "I've got one that's quit running ... that I've never seen dry before. I'm going to have to start hauling water."
The drought's impact on his operations, he says, has forced him to sell his yearling cattle, cutting his income by $80 a head. Unless the state gets its normal amount of summer rain, it could lose 25 percent of the $2.8 billion in economic activity the cattle industry generates in Arizona each year. Even with normal rains, the state still could lose 15 percent.
In Atlanta, the National Weather Service says rainfall in northern and central Georgia was so scarce between May 1998 and June 1999 that the two regions' precipitation is averaging 13 inches below normal.
Farther north, Maryland remains under a drought warning. Rainfall in parts of neighboring Virginia has dropped to as much as 18 inches below normal.
In Massachusetts, where many communities have cracked down on watering, filling pools, and washing cars, precipitation in the eastern and central parts of the state for the first half of '99 is running 5 to 8 inches below normal.
La Nia, an unusually large pool of relatively cool sea-surface water in the tropical eastern Pacific, is largely responsible for the duration of the drought, says Dr. Livezey. It emerged last year to push North America's winter storms farther north than usual, depriving Mid-Atlantic and Southeastern states in particular of the increased precipitation they ordinarily get after a long, hot summer.
"We didn't have our first real nor'easter until March," Livezey says, adding that these intense, moisture-laden winter storms typically hit in January and February. Indeed, he says, some relief came in late winter and early spring, but not enough.
Beyond the past year's trends, however, is a puzzling longer-term development: "Most of the US over the past 35 years has been getting wetter," he says. "The two exceptions are the Southeast and Mid-Atlantic regions, which have been getting drier in late spring and early to mid summer."
Ironically, meteorologists say, La Nia tends to favor formation of tropical storms in the Atlantic and Gulf of Mexico. Despite the damage they can inflict when they make landfall, these tropical depressions, tropical storms, or hurricanes may also bring significant near-term drought relief along the southern tier and East Coast, forecasters say.
Make it rain
But even as forecasters look with mixed feelings toward tropical weather for drought relief, a team of researchers from the National Center for Atmospheric Research in Boulder, Colo., is testing ways to give nature a nudge.
Working with colleagues from four universities in Mexico, NCAR scientist Roelof Bruintjes is experimenting with a new method for seeding clouds. Instead of seeding clouds with tiny silver iodide crystals in hopes of stimulating cloud formation or providing the tiny nuclei around which rain drops could form, Dr. Bruintjes is using relatively large salt crystals to encourage droplets in clouds to collide and merge into larger raindrops - the dominant process for forming raindrops, according to William Cotton, professor of atmospheric science at Colorado State University.
Begun in 1996, the four-year effort in Mexico is looking to validate earlier results.
*Guy Webster contributed to this report from Phoenix.