Radar Revolution: In Depth

Dual Pol will help us identify what the radar sees like snow, sleet, and hail.
Dual Pol will help us identify what the radar sees like snow, sleet, and hail.

MONTGOMERY, AL (WSFA) - Chief Meteorologist Rich Thomas has seen a lot during his tenure at WSFA.

"I've seen a lot of radar innovation in my 30 years here," said Thomas.

But neither he, nor the rest of the weather staff have seen anything quite like the new dual polarity radar upgrade at the Birmingham radar.

"Dual polarity radar is a game changer for us in central and south Alabama.  For those in this part of the state, we need it. We get everything…ice, snow and tornadoes.  Dual polarization radar can help us assess all of those things," said Meteorologist Josh Johnson.

"We'll have many advantages using this dual polarization radar with the beam going out in the vertical and horizontal direction. We can determine a couple different things about what's going on in the clouds. We've been showing you reflectivity on the radar for years, that's the greens, yellows and oranges showing up on how hard it's raining. Now we have something called differential reflectivity. All that means is that with the dual polarity radar scanning the sky, it's actually able to see the shape of the raindrops so we can tell how large the drop sizes are," Meteorologist Jeff Jumper said.

"This will give us an enhanced ability to tell the difference between ice pellets, snowflakes and raindrops so we can paint a more accurate picture about what type of precipitation is falling where you live," Johnson said.

And it's already had some practical applications in Alabama.

We're looking at some of this data coming in, and it was indicating that some sleet was falling in the Alexander City area on February 13th. So we sent a request out to some of the viewers in the region and sure enough there was some ground truth to that. Folks in the Alex City area were coming back and saying 'yeah we've got some sleet falling right now,' and it was actually being supported by this new data coming in from the dual polarization radar," said Meteorologist Eric Snitil.

And the applications don't end there.

"So now if you're the National Weather Service and you're about to issue a warning, and maybe you're not quite sure if you want to issue a tornado warning or not issue a tornado warning. You have a certain set of clues you're looking at. Now with dual polarity, you have even more clues. And not only more clues, but more conclusive information on whether you may have a tornado on the ground," Thomas said.

"The thing you have to realize is there are a lot of thunderstorms that rotate. That does not mean they're producing a tornado and that does not mean they will produce a tornado. So there's that fine line that we have to walk and that the National Weather Service has to walk on a regular basis when issuing these tornado warnings. When we start talking about dual polarization data, we can see the debris being lofted up into the air from a tornado…because frankly straight line winds don't do that, they don't loft anything up into the air. Only a tornado- producing storm is going to do that. The fact we can now see that thanks to dual polarization is going to change the game forever. Especially in a state like Alabama where tornadoes are our number one concern weather-wise, to be able to know with full confidence that we're looking at a tornado on the ground, the kind of damage it's doing and where it's doing it is going to be huge," Snitil said.

"The forecaster that's going to be issuing the tornado warning now has a better set of information and is sure that we have a tornado on the ground. So I think you're going to see that the warning process is a whole lot better with dual polarity," Thomas said.

The technology is new and the uses are still being explored. The applications known today may just be the tip of the iceberg.

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