BIRMINGHAM, Ala. (AP) - The National Weather Service is revamping the way it has issued severe weather warnings for decades, switching from alerts based on county lines to notices aimed at specific communities.
The new system - called storm-based warnings - is designed to predict the moment a storm will hit a community or even a certain crossroads based on radar and computer modeling programs.
Officials say the system also will make it easier to send weather warnings through cell phones, pagers or Internet-enabled handheld devices.
"A storm-based warning focuses on a storm itself and the geographic area that might be affected by it," Eli Jacks, a meteorologist at weather service headquarters in suburban Washington, said in an interview Tuesday. "We can really reduce the number of people being warned by reducing that geographic area."
A warning that in the past might cover thousands of square miles will, under the new system, be reduced to a few hundred square miles, he said.
"This is just a benefit of new technology and advances we have made in science," he said.
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.
The system, which will resemble the warnings already used by some weather service offices and many TV meteorologists, takes effect nationally on Oct. 1. While initially limited to warnings for tornadoes, severe thunderstorms, floods and marine hazards, Jacks said it would be expanded to include other threats like extreme heat.
Weather watches, which cover broad areas where storms may develop, will still be issued on a county-by-county basis, he said.
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."
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.
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.