Storm Forecasting Goes Hi-Tech

FOUR meteorologists pore over screens showing satellite images of the United States in a room where computers and lights are on 24 hours a day, seven days a week. With the flick of a mouse or touch of a button on the computer, they zoom in on various regions or states, analyzing data and looking at conditions that could develop into severe weather.

It's 9:00 a.m. at the National Severe Storms Forecast Center located on the 17th floor of a high-rise in downtown Kansas City, and the meteorologists have been on their shift for an hour. At 10:30 they gather briefly to discuss the "problem of the day" - a band of severe winds in the Southwest. Although it is tornado season, all is fairly quiet on the weather front.

Responsible for issuing severe thunderstorm and tornado watches for the lower 48 states, meteorologists at the National Severe Storms Forecast Center - one of three National Weather Service (NWS) centers - have some of the most advanced forecasting equipment at their fingertips.

"We're getting much more data than before," says Frederick Ostby, director of the National Severe Storms Forecast Center. The new technology "allows us to get a much better feel of what is going on in the atmosphere."

Some of this technology, in different form, is starting to trickle down to local offices as part of a NWS modernization and restructuring program (see related story on Page 13). At a price tag of about $2 billion, the program includes upgrading existing equipment - some of which dates to the 1950s.

"We're looking at a revolution happening now in meteorology," says Ronald McPherson, director of the National Meteorological Center in Camp Springs, Md. This technology "will have a revolutionary effect on the way weather services are delivered in this country."

Meteorologists in the severe-storms office and elsewhere say one of the most exciting advances in weather technology is the Doppler radar system. While current weather radars can only detect heavy rain, Doppler radars can also determine wind direction and speed.

The sensitive radar beam detects changes in the microwave frequency of objects in the air, such as raindrops or dust, as they move toward or away from the radar station. By calculating the frequency shift, meteorologists can see how fast the wind is carrying these objects.

The display of wind motions on a computer screen enables meteorologists to observe the formation of many tornadoes an average of 20 minutes before they touch down. Now, although forecasters identify areas in which a tornado is likely to occur, a warning is issued only after a twister is spotted.The Doppler radars are "going to be a big help in getting some lead time in tornado warnings," Mr. Ostby says. In addition, the radars can measure the amount of rain that has fallen, so forecasters are able to iss ue more detailed flash-flood warnings.

BECAUSE the center issues watches and not warnings, it has no need for its own Doppler radar but can call up data on other Dopplers located around the country. Watches indicate that conditions exist for formation of storms, while warnings mean a storm is already happening.

So far the NWS has installed five Doppler radars, and a sixth is almost on-line. By 1998 the agency says every town in the US should fall under the umbrella of one of 115 Doppler radars.

Three years ago when it was first tested, some deficiencies were found in the Doppler, but Mr. McPherson says those problems have been fixed.

"It's proven to be a magnificent tool - much more capable than we actually thought would be the case," he says. "Where they're up and running they are showing us things that we suspected might be there but had never been able to see in the atmosphere before."

Another tool meteorologists here say has been a big step forward in weather forecasting is an interactive computer system called VDUC that lets forecasters see all kinds of weather data on one screen. Users can zoom in on a particular part of the country or look at the entire earth. They can superimpose different images such as peak winds and water vapor, and plot temperatures or dew points. Until VDUC, forecasters looked at information on several screens and had to assemble data in their heads before ma king forecasts.

"When you're responsible for the whole US, there are times ... when there's a lot of severe weather in a lot of different places, and you want quick access to any part of the country," says Jack Hales, lead forecaster. "This allows you to do that."

Under its modernization program, the NWS plans to start installing a similar high-powered computer system in 1996 that will be tailored for local offices.

The National Weather Service is also testing what are called wind profilers - a network of 30 radars in the central US that point to the sky. Like the Doppler radars, the profilers also report wind direction and speed (every hour), but unlike the Dopplers, profilers don't detect precipitation and are primarily designed to measure winds in clear air.

CURRENTLY, helium balloons are launched every 12 hours to measure winds, and it is unlikely they will be replaced soon. A radiosonde attached to a balloon also determines temperature and humidity, something the profilers cannot yet do. A radiosonde is a package of meteorological instruments and a radio transmitter that measure and record upper atmospheric conditions.

But forecasters here praise the wind profilers because hourly readings provide valuable information about wind shifts in the upper atmosphere and thus help aviation forecasters issue more accurate wind conditions for aircraft. If they work well, the NWS will try to obtain funding and expand the network throughout the country, McPherson says.

"They're very helpful," Ostby says. "It would be a step backward to lose them."

For the center's 20 aviation forecasters, one of the most valuable advances in technology has been a lightning detection network, says Mike Weinrich, who issues thunderstorm bulletins to aircraft. The network, which plots individual lightning strikes as they occur, enables him and others to determine when thunderstorms begin.

While the severe storms center has had this capability for three years, federal agencies such as the Bureau of Land Management and the US Navy have operated lightning detection systems for about 10 years.

The NWS plans to acquire data from these networks and install a national system.

All these technologies help provide better models of the atmosphere and let meteorologists peer into places they couldn't see before.

Still, says Mr. Hales, we're "really in [our] infancy of understanding severe storms. We've only been at it for 30 years."