Meteorologist made forecasting a science

The Washington Post

George P. Cressman, a former National Weather Service director who took the lead in applying computers to meteorology and helped change weather forecasting from a form of cloud-gazing guesswork to a codified science, has died. He was 88.

Cressman, who was diagnosed with Alzheimer's disease, died April 17 at the National Lutheran Home in Rockville, Md.

In the 1950s, Cressman developed the first program that could produce accurate and reliable forecasts prepared by computer, which led to a monumental change in how weather is predicted and brought meteorology into the computer age.

As director of the Weather Service from 1965 to 1979, Cressman expanded the number of local weather radars, developed a nationwide weather radio network and introduced systems to provide early warnings of tornadoes and flash floods. He also made important contributions to cooperative meteorological efforts around the globe.

"He really, truly was a giant in meteorology," said Richard Hallgren, who succeeded Cressman as National Weather Service director. "Worldwide, he was extraordinarily well-known. He is one of the few who have contributed to so many things."

In the late 1940s, meteorologists were among the first scientists attempting to harness the new technology of computers. They had little sustained success until Cressman was named director of the federal Joint Numerical Weather Prediction Unit in Suitland, Md., in 1954. Using an IBM 701 computer, he recorded the weather conditions at equally spaced points around the world, then devised a program that allowed the computer to produce forecasts derived from the cumulative data.

"At the time, that was a major breakthrough," said Ron McPherson, executive director emeritus of the American Meteorological Society. "Before that was done, forecasting was mostly an art" based on extrapolations from hand-drawn weather charts.

"When computers came in, forecasting became much more of a science," McPherson added. "It started, literally, a revolution in forecasting."

George Parmley Cressman was born Oct. 7, 1919, in West Chester, Pa. After graduating from Pennsylvania State University, Cressman studied meteorology in a military course at New York University, then served as a forecaster with the Army Air Forces. In January 1943, he began teaching meteorology to military students at the University of Chicago, where he became a protege of Carl-Gustaf Rossby, a renowned meteorologist who identified the jet stream.

Cressman manned such outposts of the U.S. Weather Bureau as Lewistown, Mont., Homestead, Fla., and Mount Home, Idaho, before receiving his doctorate from the University of Chicago in 1949. He then worked at the Air Force's central weather command at Andrews Air Force Base outside Washington, seeking ways to improve the scientific validity of weather predictions. In the early 1950s, he compiled forecasts for atomic bomb tests in the Nevada desert.

In 1955, one year after Cressman began to concentrate on applying computers to meteorology, the Weather Bureau (renamed the National Weather Service in 1967) was issuing its first computer-generated forecasts. The "Cressman Analysis," or "Cressman Method," as it became known, greatly refined forecasting methods and gave rise to what meteorologists call "numerical weather prediction."

"That is an achievement that, I think, 100 years from now he'll still be known for," Hallgren said.

In the early 1960s, when Cressman was director of the National Meteorological Center, which was the government's joint military and civilian forecasting unit at the time, he instigated efforts to share weather data with the Soviet Union. He continued to expand the use of computers in weather forecasting throughout the 1960s.

As director of the Weather Service, Cressman added 100 weather radars to the national network in the 1970s and established dozens of Weather Service branches to provide accurate local forecasts across the country. He stepped down in 1979 but continued to work as a consultant to weather services in China, Spain and Brazil for several years. He was president of the American Meteorological Society and received the International Meteorological Organization Prize -- the highest honor in his field -- in 1978.

His first wife of 32 years, Nelia Hazard Cressman, died in 1974.

Survivors include his wife of 32 years, Frances Cressman, of North Bethesda, Md.; four children from his first marriage; a brother; nine grandchildren; and 10 great-grandchildren.

For The Record Los Angeles Times Thursday, May 15, 2008 Home Edition Main News Part A Page 2 National Desk 1 inches; 32 words Type of Material: Correction Cressman obituary: The obituary of meteorologist George P. Cressman in Tuesday's California section said that he worked in several remote outposts, including Mount Home, Idaho. The correct name is Mountain Home, Idaho.
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