Monthly Archives: January, 2011

A Doppler Primer

December tornadoes are not unheard of. Case in point, the first tornado I ever witnessed was on December 5, 1975. What is rather unusual is several robust supercells forming over many hours accompanied by some large, damaging tornadoes. Such an event occurred on December 31, 2010. The details from the Storm Prediction Center (SPC) in Norman, Oklahoma can be found here. As you can tell by the SPC Storm Reports Map, it was an extensive outbreak ranging from eastern OK to central IL, south to LA, MS, & AL. By all accounts, it would be a remarkable event for the spring. For this to happen on New Year’s Eve, it’s almost unheard of.

The images below are from the Jackson, MS National Weather Service doppler radar as an evening supercell was approaching the Jackson metro.

Image was captured at approximately 2302 UTC.

The couplet is very obvious in this supercell. At the time of this scan, a large tornado was moving across the densely forested areas southwest of Jackson.

The second image was scanned approximately 14 minutes later. The strong couplet is still present as the tornado continues to move northeast towards the small community of Pearl. An interesting characteristic of this image is the green area that runs from the couplet to the north/northwest. I have no way of confirming this, but what we’re seeing is likely the Rear Flank Downdraft (RFD) on the back portion of the supercell. Research conducted since the mid 1990’s has shown that the RFD is often critical to the formation of a tornado and, just perhaps, maintaining it’s strength. Nevertheless, the two images are a dramatic inside view that shows the complex inner workings of a tornadic supercell.

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