Weather service targets tornado warnings more narrowly

MONTGOMERY, Ala. — The National Weather Service is making an effort to issue fewer tornado warnings so the public will pay attention more, according to a meteorologist who deals with weather warnings.

The advance of technology in the past 10 years or so has made predicting severe weather easier, said John De Block, warning coordination meteorologist with the weather service's Birmingham, Ala., office. But the fallout may be complacency.

"There are studies that have some merit that show people become numb to hearing warning after warning," he said. "They hear a warning and nothing happens, so they don't pay attention the next time and the next time."

Weather radar now can show storms with circulation, the major indicator that a tornado may form. Those tornadoes on radar are the source of most warnings now.

"The technology is good," De Block said. "But it hasn't advanced enough yet to show us what's taking place closer to the ground. The radar may show circulation 8,000 feet above Montgomery, but we can't determine what's going on closer to the ground."

March through May is prime time for severe weather in Alabama.

On April 7, warnings were issued at 3:01 a.m. CT for Perry and Bibb counties southwest of Birmingham, and 3:13 a.m. for Dallas County west of Montgomery. The storms were part of a powerful weather system that moved through the area spawning severe thunderstorms and torrential rains.

No confirmed touchdowns were associated with the warnings. That's a good thing for the people who live in the area, but in a way it's bad for meteorologists.

"We have well-trained forecasters, and we have to trust those forecasters," De Block said. "We use all the best information available to us along with our knowledge of how the local atmosphere reacts to make the call."

The Birmingham office went to what's called a polygon warning system Oct. 1, 2007. The system defines predicted paths of tornadoes with polygons, not county boundaries, and issues warnings only for areas that are likely to experience severe weather.

That's meant to target segments of the public

Since that date, the Birmingham office, which covers more than half of Alabama's 67 counties, has issued 723 tornado warnings with 320 confirmed tornado touchdowns, De Block said.

That's a detection rate of about 77%, but De Block also calls it a false alarm rate of about 74%. Since Oct. 1, 2007, the average lead time between a tornado warning and touchdown is 16.78 minutes, he said.

As recently as 1990, the lead time was 5 minutes, according to J. Marshall Shepherd, a research meteorologist at the University of Georgia.

"We want the detection rate to be higher than the false alarm rate," De Block said. "Our position is that we would rather have the warning out there if conditions look favorable to tornadic development. We would rather have an informed public.

"That is why we are so concerned about people becoming numb to warnings," he said

Not just tornadoes can cause damage. In the roughly 6½ years since the advent of the polygon warning system, De Block's office has issued 2,922 tornado or severe thunderstorm warnings. Tornadoes, severe winds or hail caused 2,886 incidents of damage while those warnings were in effect.

The average lead time in all forms of severe weather, from the issuing of a warning to damage, is 18.53 minutes.

The public should not fixate just on tornado warnings, said Eric Jones, director of the Elmore County Emergency Management Agency.

"If there is a tornado or severe thunderstorm watch issued, you need to be aware of weather conditions," he said. "The watches mean conditions are favorable for the formation of tornadoes or severe thunderstorms. I've seen thunderstorms create 100 mph winds.

"100 mph winds are 100 mph winds; it doesn't matter if they are traveling in a straight line or going in a circle."

The weather service works in conjunction with the Storm Prediction Center in Norman, Okla., to issue weather alerts. The Storm Prediction Center works on a regional level, handling watches and informing local offices when conditions will be favorable for severe or extreme weather.

Local weather offices issue warnings, which indicate that a tornado or severe thunderstorm is imminent or occurring.

Anyone who has lived through a tornado always will take heed of warnings or watches, said Beverly Carter of Prattville, Ala.

Her home was damaged during an EF-3 tornado that struck the eastern part of the city Feb. 17, 2008. The storm packed winds of 165 mph and was on the ground for 14.5 miles.

Weather data showed that 50 people were injured and 200 homes and 50 businesses were damaged or destroyed. The city was under a tornado emergency at the time, a warning issued for populated areas when significant widespread damage and numerous fatalities are expected.

"I'll admit, before the tornado I really didn't worry about watches or warnings," she said. "Now things are different, way different. I hear a watch and I'm a nervous wreck until it passes."

When reacting to weather alerts, common sense should never be left behind, De Block said.

"In the end, it's the end user that determines what will take place," he said. "Will you take the steps to protect yourself and your family, or not?"


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