updated 1/17/2007 9:19:46 AM ET 2007-01-17T14:19:46

The National Weather Service will stop issuing countywide severe weather warnings, instead putting out warnings that are more geographically specific, the National Oceanic and Atmospheric Administration said Tuesday.

Starting this fall, the weather service will issue "storm-based warnings" for tornadoes, severe thunderstorms, flash floods and marine hazards for specific areas within a county, using well-known landmarks such as highways or rivers.

Currently severe weather warnings are issued for entire counties. Watches will continue to be issued by county. Watches indicate less imminent weather that requires awareness, but not action.

Retired Air Force Brig. Gen. David L. Johnson, director of the weather service, said storm-based warnings provide the public with more accurate information. The new warning system will take effect Oct. 1.

"These are potentially deadly, short duration events that can develop very rapidly," Johnson said at a news conference during the American Meteorological Society's annual conference.

Zeroing in
He said because of the current system, some people could be under a warning but be more than 100 miles from the weather event. In Texas, some counties are bigger than the entire state of Rhode Island, he noted.

Under the current system, for example, eight counties and nearly 1 million people would be warned, Johnson said. The new system could reduce the area warned by 70 percent and warn only about 400,000 people, he said.

Particularly in vast counties that contain a large city, the new system will help avoid causing chaos if the weather isn't likely to hit the population center, Johnson said.

At the same time, weather forecasters will still have the latitude, based on their confidence level, to recommend warnings that cover a wide enough area in case the weather takes an unexpected turn.

"I do not want to teach America to ignore warnings. So in the storm-based program, if you get the warning, there is a direct correlation to you being at risk," he said. "It's not that it's in your county somewhere, it's you're at risk, you are vulnerable."

Graphics, cell phones
Johnson said the change will improve graphical displays. He said he hopes the private sector will latch on to the new system to distribute information through methods like cell phone alerts. "You know where you are and you can see where the threat is going."

"This is a fundamental change in our warning procedures and a major enhancement in our service capability," Johnson said.

Johnson noted that while emergency managers, not the weather service, activate things like tornado sirens, this information will help them know whether to use those tools in their local areas.

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