WASHINGTON -- With nearly half the United States in the grip of a worsening drought, scientists this weekend begin scrambling to develop the first drought map ever produced by an Earth-orbiting satellite.

NASA's new $1.3 billion Terra satellite already has turned in an early engineering image of the lower Mississippi River basin. That's one of the areas where scientists are seeing near-record-low stream flows.

This image of the Mississippi Delta was acquired on February 24, 2000 and is one of the first scenes acquired by the Moderate-resolution Imaging Spectroradiometer (MODIS) on the EOS-Terra spacecraft. It covers a 62 by 62-mile (100 by 100-kilometer) area over New Orleans, Louisiana and the Gulf of Mexico. Some features clearly visible on the image are: the classic birds-foot shape of the Mississippi Rivers channels in its delta; sediment plumes around the delta and between the barrier islands to its north and differences in ocean color between the shallow bays behind the barrier islands and the open waters of the Gulf. The scene was made by combining three of the visible bands of the MODIS Land Surface Reflectance product.

Terra, the first of NASA's Earth Observing System satellites, was launched in December and reached its final orbit in late February. Its first science images are expected to be released April 19 at NASA headquarters in Washington.

"We understand drought at the ground level. But what we've never been able to do is get a full continental picture of drought, and that's the big leap we're poised for," said Steven Running, a project scientist at the University of Montana.

NOAA's National Weather Service warns that the drought has spread to nearly half the country. The dry spell, which is expected to get worse, could surpass that of last summer when more than a dozen states were declared disaster zones.

"The news is not good," Commerce Secretary William Daley told reporters earlier this month. "The drought of 1999 remains with us in the new century and our data indicate drought conditions are probably going to get worse before they get better."

Blame it on the warmest winter on record and La Nina, the phenomenon that occurs about every six to eight years. During La Nina, ocean temperatures in the eastern equatorial Pacific are unusually cold, which brings about shifts in the upper atmosphere jet stream, and often results in drier-than-normal conditions.

La Nina is the opposite of El Nino, which brings warm ocean temperatures that in turn can cause more rain to fall in some parts of the country.

The government's March 13 drought forecast -- based on the combined research of the Departments of Commerce, Agriculture and Interior -- marked the first time scientists have tried to predict a dry spell. In past years, officials at the National Weather Service simply issued a climate forecast.

But conditions now are bad enough to sound the alarm. Not only is the drought going to persist. It is almost certain to intensify.

Hardest hit will be southern Arizona, Texas, Louisiana, Mississippi, Arkansas, Alabama, Tennessee, Florida and Georgia in the south and Nebraska, Iowa, Illinois and Indiana in the north central U.S.

This year's drought is slightly different from last year's. Now the drought is moving west, into the Appalachian Mountains and the southeast, according to the USGS. Those are areas that did not get a boost in groundwater from last year's Atlantic hurricane season that battered the eastern seaboard.

Scientists are seeing near-record low stream levels in the Ohio Valley, the Lower Mississippi River Basin and in parts of the southeast.

The Mississippi River, in particular, is crucial to the health of the nation's waterways. As the longest U.S. river at 2,340 miles (3,765 kilometers), it drains 40 percent of the country's streams and rivers. Parts of the Mississippi now have stream flows at less than half of normal -- a situation that worries scientists.