Doppler Weather Radars Expected to Save Lives : Forecasts: Warning time on storms and floods will improve with use of NEXRAD. It tracks fronts by sound waves.

Weathermen are making bright forecasts for a new radar that can peer into the very heart of violent storms.

The Doppler radars now appearing around the United States are expected to save money and lives by providing earlier warnings of severe weather such as flash floods, tornadoes and thunderstorms.

“The radar allows us to see what’s going on in the atmosphere, even before a storm forms,” said Joe Friday, director of the National Weather Service in Silver Spring, Md. “And after a storm gets moving, it can map the distribution and intensity of precipitation inside it.”

Also known as NEXRAD (for next-generation weather radar), the Doppler can detect and track clouds and cloud-free fronts. Severe storms frequently develop along such fronts, and being able to track them can provide hours of advance warning time.

“The military pioneered Doppler radar technology in the 1950s by using it to help guide ground-to-air missiles,” said Robert L. Dwight, curator of the Historical Electronics Museum near Baltimore.

Civilian radars appeared in the 1960s as navigation aids on commercial aircraft. Since then, scientists have put them to many uses, including the mapping of Venus and the study of ocean waves. Police also use them to catch speeders.

The Doppler effect makes train whistles and car horns change pitch as they approach or travel away from a listener.

A Doppler radar sends out a pulse on a very stable frequency, and measures the frequency of returning signals. The frequency shift is precisely measured by the radar to determine the speed of rain or snow particles, cloud droplets or dust moving toward or away from the radar.

The first three Dopplers are operating in Sterling, just outside Washington, D.C.; Norman, Okla.; and Melbourne, Fla., near the Kennedy Space Center. Others will soon be functioning in St. Louis, the Galveston-Houston area of Texas and Dodge City, Kan.

By 1996, a network of 175 NEXRADs, to cost about $437.5 million, should be scanning the sky from national weather stations, military installations and Federal Aviation Administration facilities. Each of them will “see” clearly weather 125 miles away, and up to 200 miles in less detail.

The three Dopplers now in service have impressed forecasters. Those tracking a January storm that slammed into Maryland and Delaware with hurricane force were able to warn people around Washington, D.C., of high winds and heavy rains eight hours in advance.

“Before, the best we could have given was an hour’s notice,” said James Belville, head meteorologist at Sterling. “This was the first time a storm of this type was ever captured by radar, and, needless to say, the data are in great demand now.”

In Oklahoma, the Doppler is pinpointing tornadoes more quickly and accurately and with fewer false alarms. “The lead time for tornado warnings has averaged 19 minutes,” Dennis McCarthy, Norman’s head meteorologist, said.

Without NEXRAD, the National Weather Service’s average warning time is about six minutes between the time a twister touches down and it slashes into an area.

The national average of tornado false alarms is about 60%, but at Norman, it has fallen below 35%. Friday predicted that with the new radar, “we’re not going to be crying wolf as much as before.”

Although the radar has been proved accurate in estimating rainfall, weather experts still aren’t sure how it will do with snow.

But they are optimistic. After a January snowstorm in the Oklahoma City area, McCarthy said the radar “pinpointed very accurately which areas would receive moderate and light amounts of snow.” Based on the data he was receiving, he decided not to let some of his staff leave early. There was some muttering, but the radar correctly showed that the snow would end earlier than expected.

Few weather forecasters take snow as seriously as does Belville at the Sterling facility. “Every time I put out a warning that closes down the federal work force, it costs the government $43 million,” he said. “That puts the forecaster in a pretty tight spot.”

Using the new radar to track thunderstorms in Florida, weathermen in November and December saw small storms moving off the coast. As soon as the storms got to the edge of the warm water over the Gulf Stream, they formed rotating columns of air of the type that sometimes precede tornadoes.

“We never saw that before,” said Friday. “Now we have a strong indication that there is vigorous interaction between thermal patterns generated by the Gulf of Mexico and the weather moving over it.”