When tornado warnings are issued, a circulation in the thunderstorm is guaranteed.
BUT, only one out of four times does the tornado reach the ground.
Therefore, anything that can help confirm a touchdown is extremely important (especially at night). The new Dual Pol products from the NEXRAD Doppler Radar (which we use on Stormtracker), have a product called “Correlation Coefficient”. This new product helps detect debris being lifted up by a tornado.
The first graphic is News 2 Stormtracker in the regular “precipitation mode” or “reflectivity mode”, from last Monday night, showing the hook echo pushing through southeast Lincoln County.
The 2nd and 3rd graphics show the new Correlation Coefficient product. The dark blue indicates the debris. Huntsville NWS said it was as high as 20,000 ft. Notice in the 3rd graphic the debris has spread out and pushed into Moore and Coffee Counties (where people reported debris falling from the sky).
I wouldn’t be surprised if some of that high flying debris was the insulation from the roof of South Lincoln Elementary School.
It should be noted that some of the dark blue in the second graphic could be melting hail, as well.
So how does this product work?
In the past, the NEXRAD radar only sent out a beam polarized horizontally. It could only sense the horizontal dimensions of the target (raindrops, etc.).
The new “Dual Pol” sends out a horizontally AND a vertically polarized beam. It can sense BOTH the horizontal AND vertical dimensions of the target.
Raindrops are all the same shape and size, whereas debris is a mix of many shapes and sizes. Since the dual pol radar can distinguish between the two, it can help spot debris.
Raindrops have a high correlation coefficient while debris has a low correlation coefficient (being all different shapes and sizes, they don’t correlate much).
You can learn more from the National Weather Service’s dual pol training course by clicking here.