Ron Carl, 19, of Falls Church, had been a storm spotter for only four months in 1983 when a tornado touched down in Fairfax County about a mile and a half from his house.

"Things just didn't seem quite right that evening," he recalled. "Right around 8 p.m. it was dark out, but I heard an almost unmistakable roar. It almost sounded like an airplane in the distance."

Carl called the National Weather Service's regional office to report his findings. As many as five separate tornadoes touched down that night in Fairfax County.

Over the years, the National Weather Service has learned that not even the most sophisticated equipment can match eyewitness observations for accurate weather information, said Richard W. Schwerdt, a weather service meteorologist who works in the Washington regional office.

"It's good to get these pictures from radar, but you still need to know what's happening on the ground," he said. "We found that reports from people are still the best way to get that."

Carl is one of 400 volunteers who serve as storm spotters for the regional office. The weather service's Washington regional office is responsible for issuing storm warnings in 36 counties and cities in Maryland, Virginia and West Virginia, and keeps a close watch on the fronts with powerful radar at Patuxent Naval Air Station in St. Mary's County and with satellites operated by the National Environmental Satellite Data Service.

Although many spotters consider themselves serious weather buffs, volunteers do not need sophisticated equipment or in-depth knowledge of the weather, said Schwerdt.

The weather service provides a packet of information for new spotters that tells what type of weather to look for and how to spot the conditions that produce it.

"Severe storms, tornadoes and flash floods, they're the main three we're interested in," Schwerdt said. "Spotters also try to report high winds that produce structural damage 50 to 60 mph and hail that could damage a farmer's crop three-fourths of an inch or larger ."

After a decade of benign neglect, the Washington regional office decided to began rebuilding its spotter network last year. The first thing it did was call WRC-TV (Channel 4) meteorologist Bob Ryan.

Ryan, a firm believer in the use of eyewitness observations, developed his own extensive network of weather spotters when he came to Washington five years ago. Many now double as volunteers for the weather service.

"I don't think there will ever be a substitute for that," he said. "If we see something that looks suspicious on radar I have it flagged on a map where observers live, so I can get a first-hand report."

Last year, the regional office quadrupled the number of volunteer weather watchers who routinely report conditions in their area, and the result was noticeably better weather forecasting.

"We found that, in most cases, the sophisticated-type equipment would indicate that the storm was more severe than was the case," said Schwerdt. "Many of the warnings that were being issued for storms turned out to be false alarms."

Now, forecasters tracking storms by satellite and radar find a spotter close to the action to check with them, as well. Forecasts are based on both electronic and eyewitness observations, Schwerdt said.

The regional office is making a particular push for spotters this year in Maryland and, if recruitment efforts go well there, it intends to expand its network throughout Virginia in 1987, said Schwerdt.

The spotter network now covers the District, four counties in Maryland, three counties in West Virginia and 28 counties and cities in northern and central Virginia.

The Virginia counties include all of Northern Virginia south to a line consisting of Augusta, Green, Orange, Stafford and King George's counties. Counties farther south receive storm warnings from Norfolk, Richmond, Lynchburg or Roanoke.

The rest of the three-state region is covered by weather service offices in Baltimore and Elkins, W. Va., said Schwerdt.

Since most official weather observation posts are located at airports, volunteer spotters help fill in the gaps. Those located farther out also provide advance warning about the nature of approaching storms, the meteorologist said.

"Counties that are farther west and north are particularly important because severe weather tends to move toward the District from the west, southwest and northwest," he explained. "We like to have spotters up to 100 miles from D.C."

Typically, the regional office likes to have 25 to 30 spotters in each county, but "we can always use more," said Roy K. Smith, a weather service meteorologist who is a volunteer storm spotter in the District. "It helps to have more than you need."

Smith has his own weather instruments and keeps track of such things as temperature changes and rainfall accumulation. In the District, unusual weather usually means pea-sized hail or high winds, he said.

"I was a snow freak," said Mike Bailey, 28, of Darnestown, who became a storm spotter six years ago. "I studied it in the Boy Scouts, and bought my first weather instrument 18 years ago."

Today, Bailey has more than $3,000 worth of sophisticated electronic weather equipment at his house, most of which he built himself. He can record rainfall, minimum and maximum temperatures, wind speed, peak gusts, humidity, wind chill and a number of other weather observations.

"I know a couple of times I've called in with observations of high winds, heavy snow or thundershowers and they've altered their forecast," Bailey said.