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Waylon G. Collins
,
Charles H. Paxton
, and
Joseph H. Golden

nearly diurnal basis (e.g., Hodanish et al. 1997 ). Thus, a nearly daily challenge to National Weather Service forecasters in Florida during much of the summer is to determine which convective cell, typically among a myriad of cells, is likely to become tornadic. Anticipating tornadogenesis requires knowledge of the various tornadogenesis theories. Tornadogenesis mechanisms disseminated in the literature are typically expressed in the context of storm type. Tornadoes associated with supercells can

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R. J. Trapp
,
E. D. Mitchell
,
G. A. Tipton
,
D. W. Effertz
,
A. I. Watson
,
D. L. Andra Jr.
, and
M. A. Magsig

sampling artifacts may result in radar-observed wind speeds that grossly underrepresent the actual tornadic wind speeds. The percentage of nontornadic TVSs (i.e., gate-to-gate velocity signatures meeting TVS criteria, yet not associated with tornadoes) is unclear and has yet to be presented in the formal literature. It is likely low and is most certainly a function of algorithmic definition and range. Recent discussions of tornadogenesis failure (e.g., Trapp 1999 ), however, suggest that there are

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Aaron Kennedy
,
Jerry M. Straka
, and
Erik N. Rasmussen

) , the DRC typically occurred prior to tornadogenesis, hence making it a topic worthy of further study. With its temporal and spatial occurrence around tornadoes, the DRC could be related to the onset of tornadogenesis. If this is validated or quantified, the DRC could have use for warning decision making for tornadoes. Analysis of the DRC also may be vital in obtaining a more complete understanding of the morphology of the rear-flank appendage of the supercell and related tornadogenesis. The primary

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Antony H. Perez
,
Louis J. Wicker
, and
Richard E. Orville

1. Introduction Recent observations by Kane (1991) , Seimon (1993) , and Knapp (1994) suggest that the use of cloud-to-ground (CG) data from the National Lightning Detection Network (NLDN) in the United States (e.g., Orville 1991 , 1994 ) may be used to assist in identifying tornadogenesis. Kane describes the CG lightning characteristics associated with two tornadic supercells and observes a peak in the CG flash rate 10–15 min prior to tornado touchdown. Seimon describes an anomalous

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Amanda K. Kis
and
Jerry M. Straka

daytime and late afternoon/early evening tornadoes. For example, the depth of the inflow into the storm and tornado may change as the classical daytime mixed boundary layer transitions into the shallow nocturnal stable layer, and convection may tend to be elevated rather than surface based. Stable boundary layers have been shown in modeling studies to inhibit tornadogenesis (e.g., Leslie and Smith 1978 ), and their presence may preclude forecasts of nocturnal tornadoes. However, it is probable that

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Scott D. Loeffler
and
Matthew R. Kumjian

tornadogenesis. Fig . 3. The K DP and Z DR centroids (markers) from 1901 to 1945 UTC 24 Feb 2016 near Sussex, VA. Lines show linear fit to the centroids in order to calculate storm motion. Domain size is 110 km × 110 km. Fig . 4. Schematic depicting the separation vector. The separation vector points from the K DP centroid (red marker) to the Z DR centroid (blue marker). The vector is defined by the distance between the two centroids and the angle clockwise from the storm motion to the vector. To

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Lionel Peyraud

often supportive of supercell thunderstorms, some of which may become tornadic. For Switzerland, it was found via Houze et al. (1993) that the very weak low-level wind speeds and resultant weaker environmental vertical shear compared to U.S. storms often tended to inhibit tornadogenesis, while the mid- and upper-level wind shear were often sufficient for storms to exhibit persistent rotational characteristics (mesocyclones). As Dessens and Snow (1989) among others brought to light

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Matthew J. Bunkers
,
Matthew B. Wilson
,
Matthew S. Van Den Broeke
, and
Devon J. Healey

tornadogenesis when these more deviant right turns—relative to some baseline—occur with supercells. This degree of turning may yield additional information to help answer the question: “Which supercell, or supercells, in this group is more likely to become tornadic?” (as in Fig. 1 ). Fig . 2. (top) Schematic diagram illustrating the motion of storm cells on 26 May 1963 near Norman, OK (from Browning 1965 ; published 1965 by the American Meteorological Society). (bottom) Radar echo trajectory on 1 Jun

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Bruce D. Lee
,
Brian F. Jewett
, and
Robert B. Wilhelmson

BW2000 . The influence of mergers on tornadogenesis is also poorly understood. The observational study by Sabones et al. (1996) documented tornado occurrence coincident with the interaction between a supercell and squall line. In a similar case of squall line–supercell interaction, Goodman and Knupp (1993) suggest a potential linkage between an increase in tornado intensity and storm interaction. Wolf et al. (1996) described a case where the merging of supercells appeared to be related to

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Devon J. Healey
and
Matthew S. Van Den Broeke

Z DR arc may be indicative of near-storm environmental conditions favorable for tornadogenesis. Dawson et al. (2015) clarified that for supercells, which typically have off-hodograph motion, the storm-relative mean wind is the driver for the hydrometeor size-sorting resulting in the Z DR arc, rather than the low-level shear profile itself. Therefore, increasingly off-hodograph motion in supercells, which suggests an increased potential for tornadogenesis (e.g., Bunkers et al. 2000

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