A tornado over four miles wide? I”m trying to wrap my mind around that idea.\r\n\r\nEarlier today I listened to a recorded Powerpoint presentation by meteorologist Les Lemon on some findings on the Greensburg tornado. Now I”m chewing through a paper by Lemon and coauthor Mike Umscheid that goes into depth on what the recorded presentation, because of time constraints, could only touch on.\r\n\r\nThe findings are staggering. Bear with me, because I”m not a meteorologist and I have yet to really dig into and digest the paper. But from what I”ve gathered, radar data indicate what Lemon and Umscheid, coining a new term, have called a “vortex hole.” The hole is a part of a large-scale circulation that the authors refer to as a “tornado cyclone”–an established but rather obscure term which here seems to take on a unique application for a unique event.\r\n\r\nIn the words of Lemon and Umscheid…\r\n\r\n
Using the earlier reasoning, but in this case with a substantially larger pulse volume, we estimate actual TC [tornado cyclone] tangential velocity of 74 m s-1 or 144 kts.\r\n\r\nThis becomes even more amazing when at 0433 the radar resolved core circulation TC at 0.5o has grown to 7 km (3.9 nm) across with a mean tangential velocity of 52 m s-1 or 101 kts! The radar pulse volume at this time was 1.7 km (0.92 nm) across with this mean of 52 m s-1 (101 kts)! We recognize that by this time the radar horizon (beam center) is at ~ 1.7 km (4500 ft) altitude or just above cloud base. We, of course, don’t know if these incredibly strong velocities extend downward to the surface but we do know that damaging winds were occurring at the ground. Once again this begs the questions: What is this core circulation? Do we call this a tornado, a TC, or a mesocyclone?
\r\n\r\nI can”t feel too bad about struggling to grasp something the authors themselves are clearly shaking their heads over. I don”t do well with metric measurements, but I understand at least this much: that during its Trousdale phase, the tornado cyclone at cloud base was seven kilometers across. That”s over four statute miles. And the wind speeds were of tornado intensity.\r\n\r\nThe big question is, did the Greensburg supercell actually put down a four-mile-wide tornado? The conclusion Lemon and Umscheid make room for–staggering to contemplate–is: quite possibly. That such a mega-beast could ever exist seems beyond comprehension. Yet this, in essence, is what the authors are considering at the end of the above quote. \r\n\r\nAs if the findings in Lemon and Umsheid”s paper aren”t impressive enough in their own right, the authors corroborate them with ground-zero evidence in the form of a remarkable, firsthand log by one of the Greensburg survivors. Huddling in the basement as her house sustained EF5 damage, eighteen-year-old Megan Gardiner somehow had the presence of mind to observe what happened during the approach of the tornado and the four to five minutes it took for the vortex to pass.\r\n\r\nIf you take an interest in the Greensburg storm, Lemon and Umscheid”s paper, and Lemon”s recorded presentation, are a must. Click this link to access the presentation, together with other material on the Greensburg storm and other severe weather events delivered at the 24th Conference on Severe Local Storms in October in Savannah, Georgia.
