New radar advances weather tracking

Photo by the National Weather Service -- The radar screen at the lower left shows a tornado carrying debris as seen by new, dual-polarization radar. The screen to the upper right also uses the new technology to show wind velocity and direction of movement of the overall storm. The upper left screen shows the image using the same technology as the previous, single polarization radar, said meteorologist Tim Erickson of the National Weather Service.Photos by the National Weather Service
Photo by the National Weather Service -- The radar screen at the lower left shows a tornado carrying debris as seen by new, dual-polarization radar. The screen to the upper right also uses the new technology to show wind velocity and direction of movement of the overall storm. The upper left screen shows the image using the same technology as the previous, single polarization radar, said meteorologist Tim Erickson of the National Weather Service.Photos by the National Weather Service

New weather radar covering the Baton Rouge and New Orleans areas can pick out tornado debris, show the size of hail and allow quicker projections of flooding from rainfall, officials with the National Weather Service say.

For the first time, radar can be used to confirm tornadoes that have touched down, said Ken Graham, chief meteorologist with the National Weather Service office in Slidell.

The dual-polarization radar unit provides forecasters information to give better warnings of approaching tornadoes and hail storms, he said. Thursday night, the new radar accurately showed the size of hail in a storm in Tangipahoa Parish.

With the technology, forecasters can detect with much greater accuracy how much rain is falling in different areas and use that information in flood projections, Graham said.

The dual polarization technology is the most significant improvement in National Weather Service radar since forecasters began using Doppler in the early 1990s, said National Weather Service meteorologist Tim Destri.

Instead of the one-dimensional information provided by Doppler, the new technology bounces both horizontal and vertical pulses back from storms to give two-dimensional information to forecasters. That lets meteorologists see the size of raindrops, differentiate rain from hail and spot the debris picked up by a tornado, Destri said.

Information also includes the size of hail and the direction of the storm so the weather service can let people know when damaging hail is approaching even when nobody has seen it, said Tim Erickson, an emergency response meteorologist with the National Weather Service in Slidell.

Like hail, rain drops come in different sizes. Using a combination of drop size and rain density forecasters can give more accurate estimates of rainfall in given areas, he said.

Such information from the new radar system can be sent to the service’s River Forecast Center to help provide accurate projections of river flooding more quickly, Erickson said.

Dietmar Rietschier, executive director of the Amite River Basin Commission, said data from the new technology will be extremely valuable to emergency preparedness personnel.

“It won’t stop floods, but it will give people more time to prepare,” he said. “All of a sudden it’s like we have a lot more (rain) gauges everywhere.”

One area of improvement is in dealing with the small drops and dense rain that often dumps a lot of water on south Louisiana during warm months, Graham said.

The improved rainfall information can be used to more accurately predict flash flooding as well as river flooding, he said.

For the first time, the new technology allows meteorologists to confirm a tornado that has not been spotted by a person on the ground, Graham said.

Spotting a tornado by radar in a thunderstorm is more difficult in south Louisiana, where thunderstorms are wetter, than in places like Oklahoma, Graham said.

While the new technology does not provide additional information about when or where tornadoes will form, it helps meteorologists spot and track them once they strike, Erickson said. That’s because the new radar shows items of various sizes swirling in the funnel cloud.

The radar shows that a tornado has touched down and indicates the direction it is moving. Both facts are important in giving people a warning, Erickson said.

The new equipment also can draw the attention of meteorologists to a tornado that has touched down or to a hail storm by drawing a circle around it on the radar screen. Forecasters can zoom in on the information in that circle to get an even better understanding of what is happening, Erickson said.

Colors show meteorologists the size of the hail or debris, including tiny items and things the size of tractor-trailer rigs, he said.

In the winter, the new system will be helpful in telling forecasters the altitude at which freezing is occurring. Using that and other data, the forecasters can better predict when there will be sleet, snow or freezing rain, Erickson said.

The dual-polarization radar went on line in Slidell on March 28.

Erickson said meteorologists at the Slidell center have become confident in the information the new radar provides.

“It’s a steeper learning curve” for meteorologists than Doppler was, Graham said.

It has proven effective not only in Thursday night’s hail storm, but also in providing accurate rainfall information from recent thunderstorms, he said.

The National Weather Service radar unit in Slidell provides primary coverage from West Baton Rouge Parish to the Alabama-Mississippi border and from McComb, Miss., to 50 miles south of the Louisiana coast.

Dual-polarization radar is being installed at 160 locations at a cost of $225,000 each, according to the National Weather Service’s website.