High clouds and blue sky, snappy late autumn winds. It was not the sort of day on which meteorologist Fred A. Davis earns a tough dollar.

But just wait. Soon enough he and his colleagues at the National Weather Service will begin walking the tightrope of winter forecasting, when all their computers, radar, balloons and best judgment cannot guarantee that a predicted cold rain will not fall as a foot of snow.

Davis, the soft-spoken meteorologist in charge at the National Weather Service's station at Baltimore-Washington International Airport, is quick to acknowledge that even in the 1990s, this is a dicey field.

"It's not an exact science," said Davis. "Weather's a fascinating business . . . It's always surprising, it's always something changing."

Like that time in 1979 when the service predicted light snow. The storm stalled just off the coast and dumped about 2 feet of snow on the area. The head of runway maintenance saw fit to approach Davis at the time and deliver some information Davis already knew.

"The guy said, 'You guys missed that forecast by a mile,' " Davis recalled him saying. "No," Davis replied, "We only missed it by 2 feet."

The maintenance man was not amused. Davis does not take his responsibility lightly, but says "Basically you have to keep your sense of humor in this weather business. Your mistakes are right out front."

It's been 11 years since that storm. To this day people remind Davis of the snafu.

And now, Davis and his five-member crew of forecasters enter the trickiest time of year. Such is life on the snow line, in an area that ranks the arrival of snow about even on the anxiety scale with the arrival of the Huns.

The BWI station is one of 325 National Weather Service stations across the country, covering 17 of the state's 23 counties -- all but the westernmost counties and Prince George's and Montgomery. The forecasts prepared by Davis and his crew are sent to radio and television stations via Teletype. They also prepare special reports for boaters and pilots.

Davis said the office probably handles 150 to 200 calls a month from pilots who need information on the weather.

"The biggest challenge is probably in the winter, trying to forecast snow amounts. The rain-snow line sometimes goes between Washington and Baltimore. You might get freezing rain, sleet or snow."

To get a fix on the form precipitation will take, Davis and the five forecasters who work at BWI check information from other weather stations on the path of approaching cold fronts. They also look at the high-altitude temperature readings taken from weather balloons launched twice a day from Dulles International Airport. But Dulles is about 50 miles away, and those readings are not always valuable for predicting snow or sleet or cold rain around the suburbs of Baltimore, Davis said.

He expects forecasting to take a leap forward in the next few years as the Weather Service introduces more sensitive radar and more advanced instruments for measuring wind. He says this will make storm forecasts more accurate. And storm forecasting is the name of the game.

"We don't earn our money saying 'Partly sunny,' " Davis said. "The accuracy of the severe forecast is the main thing."

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