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Brynn W. Kerr
and
Grant L. Darkow

focus of the research com- munity ( e.g., Browning 1964; Lemon and Doswell 1979; Klemp 1987) , other studies have acknowledged the generally weaker, but occasionally quite damaging, nonsupercell tornadic storm ( e.g., Wakimoto and Wil- son 1989) . Although many questions with regard to the devel- opment and evolution of tornadoes remain unresolved, much has been learned about the storm-scale processes leading to tornadogenesis since the Thunderstorm Pro- ject ( Byers and Braham 1949) , the first

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Alexandra K. Anderson-Frey
,
Yvette P. Richardson
,
Andrew R. Dean
,
Richard L. Thompson
, and
Bryan T. Smith

of the environmental parameters associated with an environment conducive to tornadogenesis. We know that the combination of 0–6-km vector shear magnitude (SHR6, the magnitude of the vector difference in winds between the surface and 6-km height) and mixed-layer convective available potential energy (MLCAPE) provides a good first estimate of supercell potential ( Brooks et al. 2003 ), with at least marginal CAPE necessary to fuel the updraft and SHR6 essential for developing the midlevel rotation

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Matthew J. Onderlinde
and
Henry E. Fuelberg

tornadogenesis (e.g., McCaul 1987 ; Spratt et al. 1997 ; Suzuki et al. 2000 ; McCaul et al. 2004 ; Edwards 2008 ). However, these TC-related supercells often are shallower and smaller than their midlatitude counterparts ( McCaul and Weisman 1996 ). These differences must be considered when forecasting TC-related tornadoes. The magnitude of instability (e.g., CAPE) appears to be less important in TC-related tornadoes than in midlatitude scenarios. Indeed CAPE typically is observed to be considerably

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Max L. Dupilka
and
Gerhard W. Reuter

vector magnitude did not. These and other studies (e.g., Kerr and Darkow 1996 ; Rasmussen and Blanchard 1998 ; Monteverdi et al. 2003 ) emphasize the important point that severe thunderstorm and tornadoes occur within a broad range of shear and CAPE environments. It is extremely important to keep in mind that it is likely the interaction of a number of physical processes that leads to tornadogenesis, and these processes may (or may not) be well represented by particular environmental parameters or

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David L. Andra Jr.
,
Elizabeth M. Quoetone
, and
William F. Bunting

anticipate intelligently storm evolution and threat and therefore the range of potential outcomes necessary to determine warning content. For example, a tornado is more likely to occur with a classic supercell than a bowing squall line, where damaging wind is often the primary threat. Consider the case of the collapsing supercell: the disappearance of the reflectivity hook and lowering of the storm top could suggest a weakening storm, or, in the eyes of an expert, it might signal tornadogenesis ( Lemon

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Timothy A. Coleman
and
P. Grady Dixon

versus tornado count–tornado days As illustrated by Dixon and Mercer (2012) , large differences in spatial patterns can occur if one uses point analysis [i.e., the point of tornadogenesis; e.g., Brooks et al. (2003) ] instead of pathlength analysis (e.g., Dixon et al. 2011 ). Given that the pathlength of a tornado is much more proportional to the area it affects, its destructive capability, and its overall impact on the risk of a tornado striking an area within its radius of influence in the KDE

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Roger Edwards
and
Richard L. Thompson

.g., Davies-Jones 1993 ; Markowski et al. 1998b ). For example, our reconstructions of KGD07 ’s 2300 UTC Fig. 17 (our Fig. 1a ), but valid at 0100 UTC (our Fig. 1b ), 25 min prior to the tornado report, indicate less of what KGD07 deem, “an environment that could enhance low-level stretching beneath cloud bases and within the lower portion of sustained updrafts,” closer to actual tornadogenesis than at the 2300 UTC time that KGD07 selected. Yet conditions in the actual atmosphere, on some scale, 2

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Robert J. Trapp
,
Sarah A. Tessendorf
,
Elaine Savageau Godfrey
, and
Harold E. Brooks

radar scans collected by the Jackson, Mississippi (KJAN), Weather Surveillance Radar-1988 Doppler (WSR-88D; see Trapp et al. 1999 ). Hence, as in the other cases of QLCS tornadoes preliminarily investigated by Trapp et al. (1999) , traditional radar-based indicators of impending tornadogenesis likely offered little operational tornado-warning guidance for this event. And since this example (which is one of several) of QLCS tornado occurrence happened during the overnight hours, guidance from storm

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E. De Wayne Mitchell
,
Steven V. Vasiloff
,
Gregory J. Stumpf
,
Arthur Witt
,
Michael D. Eilts
,
J. T. Johnson
, and
Kevin W. Thomas

strong azimuthal velocity gradient was observed coincident with the developing hook echo. Later, the first pulsed Doppler radar observation of a tornado was made during the Brookline, Massachusetts, tornado on 9 April 1972 ( Kraus 1973 ). Interestingly, no hook echo was observed at the time of the tornado; however, a hook echo was observed prior to tornadogenesis. In 1973, the National Severe Storms Laboratory’s 10-cm pulsed Doppler radar scanned through a tornadic thunderstorm near Union City

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Richard L. Thompson

discriminating between tornadic and nontornadic thunderstorm environments ( Weisman and Klemp 1982 ; Stensrud et al. 1997, hereafter SCB97 ). In the BRN denominator, as calculated by SCB97, U avg is defined as the magnitude of the difference between the 0–6-km density-weighted mean wind and the density-weighted mean wind in the lowest 0.5 km: BRN shear = 0.5( u avg ) 2 . Numerical simulations of supercells have begun to elucidate processes relevant to supercell tornadogenesis, and the

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