updated 9/18/2007 3:58:40 PM ET 2007-09-18T19:58:40

The National Weather Service is revamping the way it has issued severe weather warnings for decades with a new system designed to mark a geographic bull's eye where a storm will hit.

The system, set to be announced Monday, switches from alerts based on county lines to notices aimed at specific communities, weather service officials told The Associated Press on Tuesday. Using radar and computer modeling programs, the system is meant to predict the moment a storm will hit a community or even a certain crossroads.

Known as storm-based warnings, the new alerts could reduce a warning area from thousands of square miles to a few hundred square miles, experts said.

"A storm-based warning focuses on a storm itself and the geographic area that might be affected by it," said Eli Jacks, a meteorologist at weather service headquarters in suburban Washington. "We can really reduce the number of people being warned by reducing that geographic area."

When it takes effect nationally Oct. 1, the new system will initially be limited to warnings for tornadoes, severe thunderstorms, floods and marine hazards. Later, it will be expanded to include other threats like extreme heat, Jacks said.

County-by-county tradition
Tornado forecasting began in the late 1940s, and the government started issuing weather warnings in the 1950s based on a network of storm spotters with radios and telephones. Warnings generally have been issued on a county-by-county basis ever since.

Under the new system, the weather service plans to issue warnings for specific storms and alert people who might be in the path. On a radar map, the warned areas appear as highlighted polygons rather than entire counties; forecasters will refer to commonly known landmarks like rivers and roads in written announcements.

Officials say the system also will make it easier to send weather warnings through cell phones and other handheld devices.

Some weather experts are concerned that radar has its limits and a fast-moving storm can change direction, suddenly taking aim at an area not mentioned in the storm warning. But Jacks said the system will be able to keep up with abrupt changes.

A report by the National Oceanic and Atmospheric Administration predicted the new system would save $100 million annually, mainly by cutting back on unneeded business closings and the amount of time people spend huddled in closets or basements during warnings.

"I think that is a very conservative estimate. It could be substantially more," said Daniel Sutter, who calculated the savings and is an associate economics professor at the University of Texas-Pan American.

Tests already done
The new warnings have worked well during trials in Indiana, said Dave Tucek, who coordinates severe weather warning in the agency's Indianapolis office.

"I think it has been a good system," said Tucek. "The idea behind it ... is that there is no reason to warn the northern end of a county about something that is in the southern end of a county."

The president of the Alabama Skywarn Foundation, Brian Peters, said the new system already is being used in some weather service warnings, which name a county being placed under alert and then specify a certain area that's particularly at risk.

But, he said, highlighting too narrow an area for a warning could be hazardous since storms can change direction, and radar has its limits. An undetected tilt in a twister could send it toward an area that was not under a warning if alert boxes are too small.

"That's what worries me, giving people a false sense of security," said Peters, a meteorologist with WBMA-TV in Birmingham who previously worked as the weather service's warning coordinator for Alabama.

Jacks said new warnings will be issued as storms move.

"You can issue as many storm-based warnings as you need," he said.

Copyright 2007 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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