Initiation to Dissipation -- Smithville, MS Tornadic Supercell

I'll be starting a new series on this blog called Initiation to Dissipation. I'll be using radar images from the historic April 27 tornado outbreak to show the life cycle of some of the worst tornadic supercells and some of the most impressive signatures during their life cycles. The first supercell featured will be the one that produced an EF-5 tornado in Smithville, MS.


Convective initiation of this supercell began around 1643Z in Northeast Louisiana near Rayville.


Over the course of the next hour, this storm strengthened and began to develop a weak mesocyclone. Within the storm's first hour, it initially had a difficult time time separating itself from other convection. It's possible that hodographs were not as strongly curved in the lowest three kilometers, thereby making deep layer shear vectors more parallel to the pre-frontal trough that the storms initiated along.


By 1843Z, however, hodographs appeared to become increasingly favorable for semi-discrete supercells. In fact, the storm had clearly became separated from other convection and even had unimpeded inflow into the updraft region. Weak supercell characteristics were seen by this time with as a weak echo region (WER) was present along with a weak, persistent mesocyclone.


An hour later, the supercell appeared to be entering its mature stage. Distinct supercell characteristics were noted, including the presence of a WER, a bounded weak echo region (BWER), a strong mesocyclone, and a hook echo.


By 2042Z, the supercell is located near Smithville and likely near its peak intensity. A very tight concave reflectivity gradient is present in the inflow region of the supercell, a very impressive WER and BWER were also present, a hook echo persisted, and a very strong low and mid-level mesocyclone were still present.





A zoomed in image of the supercell west of Smithville (left) shows an impressive BWER at around 9,300 feet. As the supercell moved northeast of Smithville, a tornado signature can be seen in the storm relative motion data along with a very high normalized rotation (NROT) value typically only seen in intense mesocyclones and tornadoes.


By 2142Z, another cell had merged with the supercell and seemed to interfere with its structure. Nonetheless, a strong mesocyclone remained present along with a WER.


The supercell remains in tact another hour later, but it's clearly not as well-defined as it once was over Northeast Mississippi. It also becomes apparent that convection to its south may likely further disrupt the updraft.


Indeed, by 2343Z, the storm has weakened considerably and shows no signs of supercell characteristics.


By 00Z, the storm had pretty much dissipated but not before traveling a total of about 437 miles!

Damage Survey Images