May 14, 2014 Bullitt County EF-0 Tornado

May 14, 2014 Bullitt County EF-0

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Below are several radar images highlighting the brief tornadic circulation as seen by the Terminal Doppler Weather Radar for Louisville International Airport. Red values are picking up hydrometeors moving away from the radar and green values are picking up hydrometeors moving toward the radar. The tight "couplet" of reds/greens pictured below is indicative of counter-clockwise circulation. The first radar image is at 223 PM EDT, which is when the tornado touched down just south of Brownington in Bullitt County.

The next image below is the radar at 226 PM EDT, just before the tornado lifted. Notice how the tight circulation has moved from just south of Brownington to just east-northeast of Brownington.

The final image below is a 4 panel of various radar data, including a few dual polarization products. The upper left image is of regular reflectivity. You see a low-topped supercell with the tip of the "hook echo" highlighted in white. Tornadoes occur near the tip of the hook in supercellular storms. The bottom right image is the dual polarization Correlation Coefficient product. This product measures the uniformity of objects in the air that the radar beam is bouncing off of. For instance, if you have a very uniform steady rain where the rain drops are all about the same size, you will have a Correlation Coefficient very near 1. However, if you have situation where objects in the sky are many different sizes (not uniform) then your Correlation Coefficient is much lower. An example of this would be if there were debris lofted into the air. In some cases when a tornado occurs close enough to a radar, a TDS (Tornado Debris Signature) can be seen using the data below. Notice how the lower right panel has an area of much lower CC values, matched up perfectly with the tip of the "hook echo" in the upper right. Now take a look at the lower left panel. Sometimes if your CC values get too low, your Specific Phase Differential (KDP) values go missing. One other clue would be if you suddenly get very high reflectivity values in the tip of the "hook echo". If you can follow these features over a couple of volume scans, and they move with the tip of the "hook echo" it is very likely you have a TDS signature and that a tornado is already occurring. This seems to be a good example from the May 14th Bullitt County EF-0, which happens to be very close to the Terminal Doppler Weather Radar in northern Bullitt County.


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