The Forecast Is for Accuracy

National Weather Service adds more science to an old art

You don't need a computer to tell which way the wind blows, but your local weather forecaster does. Twice a day a National Weather Service computer in Suitland, Md., provides meteorologists all over the country with the basic material for their predictions: temperature readings, weather maps, storm warnings. Though weathermen remain the objects of joking more than of genuflection, computers have steadily increased the accuracy of their forecasts by about half a percent a year over the past 15 years. Now, thanks to some new machinery being installed at NWS headquarters and its 280 local offices, that modest rate of improvement could jump like the mercury on a hot summer morning. Some examples:

> A supercomputer for the Suitland weather center, due to come on line next summer, is expected to double the accuracy of the weather service's daily forecasts. The $16 million Control Data machine, one of the world's most powerful, will take over much of the service's main data-processing task: combining more than 100,000 local weather readings from satellites, airplanes, balloons, ships and 10,000 surface stations into a single, enormously detailed numerical model of the earth's weather. Crunching through this mass of data at more than ten times the speed of the IBM computer now in use, the new machine should by decade's end make eight-day forecasts as accurate as four-day forecasts are today.

> A computer program developed at the University of Wisconsin may take some of the surprise out of sudden summer squalls and tornadoes. Called MCIDAS (for Man-Computer Interactive Data Access System), the program uses some fancy extrapolation techniques to help local storm watchers locate pockets of impending bad weather that are too small to be picked up by the national weather-monitoring systems. On a cloudless morning in Wisconsin recently it correctly predicted, six hours in advance, severe thunderstorms in the northern part of the state.

> A modernization program scheduled to be completed in September is already changing life for local forecasters, whether they are blow-dried TV personalities or the salty voices on marine weather radio. By installing minicomputers and video screens at its regional offices and connecting them to its nationwide computer network, the NWS's new Automation of Field Operations and Services (AFOS) is eliminating the need for the paper weather maps and long rolls of teletype that once decorated the walls of every weather office. Using AFOS, a meteorologist summons up on a video screen the weather service's national data, presses a button that superimposes more detailed readings from nearby observation posts and presses another key that zooms in on his state or county for an up-to-date rundown of the local weather. Some weathermen remain skeptical, as one Midwestern forecaster puts it, as to "whether AFOS computers will actually improve forecasts or give bad forecasts more frequently." But NWS Director Richard Hallgren has no such doubts. "The larger the computer, the better the forecast," he says. "As the computer gets bigger, we can get more of the mathematics and physics of the atmosphere into our models."

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