NORMAN — The target of the forecast shifted quickly.
On Dec. 19, forecasters at the National Weather Service office in Amarillo, Texas, had called for possible blizzard conditions just outside their windows in the center of the Panhandle. But as the system got closer to Texas, the dual-polarization radar they'd been using for less than two months offered a much clearer picture. Amarillo was about to receive a little snow and a good rain, but the northern counties were about to experience the blizzard.
Jose Garcia, meteorologist in charge of the Amarillo office, which covers the Texas and Oklahoma panhandles, said the forecast was able to be adjusted because of the dual-polarization radar. That technology soon will be in use throughout the National Weather Service coverage area based in Norman, meaning meteorologists in that forecast office will have the same tool going into this winter.
Conventional Doppler radars send out a horizontal pulse that allows forecasters to see precipitation, but can't tell the difference between rain, snow or hail, said David Andra, meteorologist in charge of the Norman Forecast Office. Dual-polarization radar sends and receives horizontal and vertical pulses, providing a much more informative picture of what is out there.
This information helps meteorologists identify rain, hail, snow or ice pellets, improving forecasts.
“It helps us understand what we see on the radar and have been seeing on the radar for many years,” Andra said. “It helps us be more confident that what we see is wet snow or dry snow or it's rain or it's heavy rain. It just allows us to be more confident and specific with our information.
“It won't make any difference in the forecast several days before or in the lead-time information for tornadoes. However, in the very short-term, when the rain or snow or whatever is ongoing, we hope that we can be more specific as to what it is that is falling out there. And if we know what's falling upstream, let's say from Oklahoma City, with some confidence, we can better tell what's likely going to happen in Oklahoma City maybe three hours from now when it moves into our area,” Andra said.
During the Dec. 19 storm, Amarillo got between 1 and 3 inches of snow, while areas in the northwest Texas Panhandle and the Oklahoma Panhandle received 6 inches to a foot of snow. Areas including Kenton in the far western Oklahoma Panhandle received 12 inches of snow or more.
Garcia said that was the first of two real tests for Amarillo's dual-polarization radar. The latter came in April. Supercell thunderstorms erupted across the Texas Panhandle in the afternoon hours April 11, and one storm produced a vast quantity of pea- to golf-ball-size hail across U.S. 287 that buried cars up to 4 feet deep.
“That developed and could be seen clearly in the dual-pol products,” Garcia said. “You can really see very vividly where that hail was falling and the specific location. I think that's going to really help us in the future to be able to pinpoint and look at products like that being generated by the dual-pol.
“It provides a lot more specific information to protect people out there and help them understand what's going on.”
Andra has been with the National Weather Service in Norman more than 25 years. He's seen changes.
“With the old WSR-57 radar, you essentially sat in front of a console that showed a black and white image,” he said. “Going to Doppler, it was kind of like going from radio to color television. Now the change to polarimetric data in the radar will be more like going from regular color television to HD. ... I think it is a change that everyone will benefit from.”
Andra said the technology allows forecasters to look at things such as the differences of the returned energy between the vertical phase and the horizontal. That provides details about the shape of the particle they are sampling. To really use polarimetric radar data takes a combination of different pieces of information that come back from the radar, he said. Those are compared.
“Certain combinations yield or infer different types of precipitation or droplet sizes, or in some cases, non-weather echoes, such as birds or insects,” Andra said. “We look at a combination of those, and for weather we also look at the time of year, and that tells us what is out there.”
Norman has three radars in its coverage area: one at Frederick in southwest Oklahoma, one near Lake Stanley Draper in Oklahoma City and one at Vance Air Force Base's Kegelman Auxiliary Airfield near Great Salt Plains State Park. The dual-polarization operation has been used at the latter since March 2011. The other two are expected to have dual-polarization this month.
The National Weather Service's Tulsa Forecast Office has two radars in its coverage area, one near Inola and one near Fort Smith, Ark. Both are dual-polarization. The coverage area for the forecast office at Shreveport, La., includes McCurtain County in far southeastern Oklahoma. That office has one radar that is scheduled to be operating in dual-polarization by year's end.
“Having this go into operation now gives us a chance to develop some confidence with the information,” Andra said. “It's actually quite a bit more complicated to interpret than the traditional Doppler radar information that we've worked with for many years, but everyone on our staff who is going to be making a warning or forecast decision will have been trained before these systems are operational.
“And I would say our staff in Norman is a little more experienced to begin with because we were part of a research test product several years ago when this system was still being developed.
“This will put us in a good place for the upcoming winter weather season and then the following spring severe weather season.”