Your quote: "That tornado really reminds me of Yazoo City a lot, spawned by a long-tracked, most definitely discrete supercell resulting in the tornado being able to maintain itself until the supercell likely got choked off by convection, or entered a more unfavorable environment."
Was this the kind of setup that spawned the Tri-State tornado (sorry if that seems like a silly question)?
The Tri-State Tornado was spawned by a supercell that was located right along the surface low, riding at the intersection of the warm and cold fronts, also known as a "Triple Point." The supercell was able to form in an initially capped environment due to advanced forcing from the cold front, which allowed the supercell to form. The supercell's location at the Triple Point also gave it access to the best tornado-conducive conditions in the whole warm sector, where enhanced turning from the warm front enabled the Tri-State Supercell to produce a tornado, giving it access to the most favorable tornado-conducive wind profiles in the warm sector. Slightly southwesterly winds further south prevented other supercells, which eventually initiated to the south of the main Tri-State Supercell from dropping tornadoes while the main Tri-State Tornado was ongoing, although they likely would have exhibited some rotation aloft. The supercell's proximity to the surface low also gave it access to the highest shear values. The mid-latitude cyclone that spawned the Tri-State Tornado wasn't particularly intense while the Tri-State Tornado was ongoing (estimated at above 1000 mb), which would have allowed the Tri-State Supercell to interact with shear values high enough to generate a violent tornado, but not shear values too high, that would shear apart an updraft and kill storm potential. The supercell's proximity to the surface low also resulted in it having a very low base, which was most definitely not the case with the other supercells further south. From all available knowledge, the supercell appears to have immediately began rotating and producing the Tri-State Tornado right after it became supercellular.
The reason why other big tornadoes occurred along with the Tri-State Tornado (in Kentucky and Tennessee), despite the unfavorable conditions further down in the open warm sector while the main Tri-State Tornado
was in progress was the fact that the mid-latitude cyclone began to move faster to the northwest as the day progressed, which increased shear values and wind profiles after the Tri-State Tornado dissipated. The Tri-State Tornado's dissipation was likely related to a convective merger, as all accounts have the tornado quickly weakening after striking Princeton. Another Tornado (which is unrated but I believe it was an EF3 or EF4) was most definitely generated by the same supercell further north in Indiana about an hour after the Tri-State Tornado dissipated, which most likely indicates that this tornado was a result of the supercell undergoing a cycling process. This is similar to the supercells of April 27, 2011. The Cullman Tornado dissipated as it's parent supercell had its inflow obstructed by nearby convection, resulting in it gradually weakening near the Arab, AL area before dissipating at the Guntersville Dam area. The supercell gradually developed a new mesocyclone, and eventually dropped a new tornado to the northeast near Pisgah, AL. Almost all of the dissipations of major tornadoes on April 27, 2011 were a result of convection obstructing the inflow notch, supercells merging with other convection (Philadelphia-Cordova Supercells), or the supercell simply moving into an environment that was no longer conducive for tornadoes. It's likely that the Tri-State Supercell's cycling process was like this as well, but there is no way to tell. The only tornadoes that had their parent supercells remain unobstructed for long periods of time on 4/27/2011 were the Enterprise, MS EF4, and the Hackleburg EF5. Both lasted over 100 miles.
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