Clash of warm, cold air spawned rare Md. tornado

October 20, 1990|By Luther Young

It wasn't a Midwest-sized tornado, but it was a classic twister, giving Marylanders a rare look at a violent force of nature that has visited the state only 100 times in the last 41 years.

And the late-afternoon storm that injured nine residents and caused extensive property damage in the Chartley and Glyndon areas of Baltimore County on Thursday was typical of many of those tornadoes, right down to the initial uncertainty about whether it was really a tornado.

"It was small and fast-moving, in the heart of a violent thunderstorm," said Fred Davis, the chief National Weather Service meteorologist at the airport who was responsible for officially labeling the storm. "And no one ever saw a funnel."

Mr. Davis upgraded his initial severe thunderstorm assessment to tornado after traveling to the scene late Thursday and finding "trees twisted and broken, cars spun around. It's the signature I look for, and it was there."

Born of the collision of a Canadian cold front surging in from the west and wet, warm air from the south, the tornado lived only an estimated three minutes on a southwest to northeast course.

But the circular winds, howling at 75 to 100 miles an hour, wreaked havoc along a path 100 yards wide and one-eighth of a mile long, Mr. Davis said. Those winds place the tornado in the least severe of five categories; the most violent can reach speeds of 300 miles an hour.

The total damage track was larger, however, due to high winds in the thunderstorm and the suspected presence of "downbursts" -- columns of cold air that can suddenly plunge from storm clouds, strike the ground and flare out at speeds up to 100 miles an hour.

"They can cause as much damage as tornadoes," said Fred Ostby, director of the National Severe Storms Forecast Center in Kansas City, who added that eastern tornadoes are "very difficult to forecast" and are often part of "real strong systems" that can spawn downbursts.

The National Weather Service has tracked an average 786 tornadoes annually during the last 30 years, ranging from 116 a year in Texas to just one twister in Alaska since 1960. Fatalities have averaged 82 a year in that time.

Maryland ranks 35th in annual frequency of tornadoes, at two to three a year, and 36th in fatalities: only two since 1950 -- on May 19, 1967, in Garrett County, and on May 8, 1984, in Dorchester County.

Tornadoes have caused 50 injuries in the state from 1950 through 1989, with 10 the largest number inflicted by a single storm, on June 29, 1980, in Harford County. The nine injuries from Thursday's tornado rank it second, Mr. Ostby said.

His files contain two more tidbits about Maryland tornadoes: Baltimore County has experienced only three since 1950 -- in 1973, 1978 and 1979 -- and the storm represented only the third October tornado in the state in 41 years.

"They have a system of volunteer tornado spotters out West," a network that has greatly aided forecasters in alerting residents to an approaching tornado, said Mr. Davis. "If we had spotters here, they might have to wait 10 years to see one."

By early next year, the National Weather Service is expected to have installed at its Washington forecast office in Sterling, Va., a high-tech Doppler radar that can give important new information about winds.

It will cover the Maryland area and "should help a lot," said Jim Belville, meteorologist in charge at the Washington office.

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