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Ernest Agee
and
Erin Jones

that the strongest tornadoes (F5/EF5) are most likely produced by mesocyclonic supercell storms (see Trapp et al. 2005 ), such as the events in Moore, Oklahoma, on 3 May 1999; in Greensburg, Kansas, on 4 May 2007; and in Parkersburg, Iowa, on 25 May 2008. These tornadoes (defined as type I) are produced by a strongly rotating updraft interacting with a rear-flank downdraft, although most supercell tornadoes are weaker and some may not require the RFD for tornadogenesis. Other types of tornadoes

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Joshua M. Boustead
,
Barbara E. Mayes
,
William Gargan
,
Jared L. Leighton
,
George Phillips
, and
Philip N. Schumacher

boundaries. 2. Methodology Significant tornadoes for the years 1979–2011 for parts of the central and northern plains were compiled using the National Climatic Data Center (NCDC) publication Storm Data ( Fig. 1 ). For each tornado occurrence, archived surface observations were obtained and plotted using the Digital Atmosphere program for a period of 2 h before to 1 h after tornadogenesis. Hand-drawn analyses of temperature, dewpoint, and pressure were completed for each of the hours. Using the manual

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Stephan B. Smith

’s view by the Hesston anvil), and was important in triggering tornadogenesis. Second, the authors highlight the fact that the Hesston storm did not become tornadic until approximately 105 min after it was first detected on radar. They state, “This is a relatively long delay for an active thunderstorm to become tornadic in an environment favorable for strong tornadic activity.” However, an examination of other notable tornadic storm cases reveals that lags of even greater duration have occurred. The

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Mace L. Bentley
,
Michael Buban
, and
Stonie Cooper

an additional 10 min. Observational studies of tornadic thunderstorms and their associated environments have been numerous over the past several decades ( Miller 1972 ; Purdom 1976 ; Maddox et al. 1980 ; among others). A consistent finding through many of these investigations has been the proximity of thermal boundaries near the region of tornadogenesis. The alteration of the mesoscale wind and thermodynamic fields by boundaries has been shown to produce a more favorable environment for the

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Sarah M. Stough
,
Lawrence D. Carey
,
Christopher J. Schultz
, and
Phillip M. Bitzer

-based straight-line winds, and undergo tornadogenesis ( Lemon and Doswell 1979 ; Markowski and Richardson 2009 ; Duda and Gallus 2010 ; Davies-Jones 2015 ). Though tornadogenesis remains an active area of research, this study specifically addresses the mesocyclone in lieu of tornadic rotation because of the shared dependency of lightning and the mesocyclone on the midlevel updraft. Current tornadogenesis research establishes the role of the mesocyclone as a necessary but insufficient component related to

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Daniel T. Lindsey
and
Matthew J. Bunkers

hodograph curves in a clockwise direction, while the hodograph in the 2–4-km layer exhibits counterclockwise curvature. This low-level clockwise curvature is favorable for tornadogenesis in the right mover, but unfavorable for the left mover since positive streamwise vorticity would enter the left mover’s updraft near the surface ( Davies-Jones et al. 2001 ). Accordingly, the 0–1-km SRH was 157 m 2 s −2 (−46 m 2 s −2 ) given the observed motion of the tornadic right-moving (nontornadic left moving

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Jacob H. Segall
,
Michael M. French
,
Darrel M. Kingfield
,
Scott D. Loeffler
, and
Matthew R. Kumjian

of supercellular tornadoes is achieved by identifying known features or ongoing processes in operational remote sensing data that are thought to indicate that tornado formation or evolution is imminent. Many observational studies have investigated the tornado’s life cycle using mobile and airborne radar data with a focus on the tornadogenesis process (e.g., Brandes 1977 ; Dowell and Bluestein 2002a , b ; Bluestein et al. 2003; Wurman et al. 2007 ; Markowski et al. 2012 , 2018 ; Kosiba et al

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Erik N. Rasmussen
and
David O. Blanchard

of the various parameters is compared in an objective manner in section 8 . The results of this investigation are summarized in terms of tornadogenesis and supercell-favoring environments, and tornadogenesis failure modes, in section 9 . 2. Methods a. Sounding database The soundings evaluated here are contained in Rawinsonde Data for North America, 1946–1992 (Forecast Systems Laboratory and National Climatic Data Center 1993) and were all made at 0000 UTC nominal sounding time from the U

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Max L. Dupilka
and
Gerhard W. Reuter

convective available potential energy (MUCAPE)], and the bulk Richardson number. The purpose of this paper is to further explore which characteristic sounding features are supportive for tornadogenesis, and which sounding parameters could help to make a probabilistic distinction between the occurrence of weak and strong tornadoes. The results presented in Part I indicate that significant tornadic storms tended to have larger shear values than both weak tornadic and nontornadic severe storms. In

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Brian A. Colle
,
Kelly A. Lombardo
,
Jeffrey S. Tongue
,
William Goodman
, and
Nelson Vaz

, with the maximum frequency occurring between May and August. There is a peak in July, due to the seasonal lag in the availability of low-level moisture for this flow regime ( Johns 1982 ). During periods of northwest flow, there is an average of ~15° of directional shear between 850 and 500 hPa over the northeast United States ( Johns 1984 ). For the other wind patterns, tornadoes develop with little (<5°) directional shear in this layer. Most of the analysis of tornadogenesis over the northeast

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