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David M. Schultz
,
Yvette P. Richardson
,
Paul M. Markowski
, and
Charles A. Doswell III

terrain of the Rocky Mountains, and vertical wind shear) are closely tied to the pole-to-equator thermal gradients, but the mere presence of those gradients on the synoptic scale is no guarantee that these ingredients will be brought together to produce tornadoes in any specific extratropical cyclone. Horizontal temperature gradients also exist on the storm scale. Temperature gradients associated with downdrafts and outflow are likely important in tornadogenesis in supercells (the most violent

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Joshua Wurman
,
David Dowell
,
Yvette Richardson
,
Paul Markowski
,
Erik Rasmussen
,
Donald Burgess
,
Louis Wicker
, and
Howard B. Bluestein

VORTEX2 is the largest, most ambitious study focused on improving our understanding of tornadoes, including tornadogenesis, tornado structure, and improving forecasts. Nearly all of the most intense tornadoes, those capable of causing the most widespread damage and largest number of fatalities, are spawned by supercell thunderstorms. Recently, computer models and observing technology used to study supercells have become more accessible and increasingly sophisticated, enabling detailed

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Leigh Orf
,
Robert Wilhelmson
,
Bruce Lee
,
Catherine Finley
, and
Adam Houston

(VORTEX2) ( Wurman et al. 2012 ), have provided insight into these processes, but forecasting tornadogenesis within an already-formed supercell remains a formidable challenge. Seminal numerical simulations of supercell thunderstorms conducted in the 1970s and 1980s (e.g., Klemp and Wilhelmson 1978a , b ; Schlesinger 1980 ; Rotunno and Klemp 1982 ; Weisman and Klemp 1982 , 1984 ; Rotunno and Klemp 1985 ) were the basis from which scientific theories of supercell formation, strength, and

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Nolan T. Atkins
,
Kelly M. Butler
,
Kayla R. Flynn
, and
Roger M. Wakimoto

chosen for analysis. The radar reflectivity and copolar cross-correlation coefficient were objectively analyzed to a Cartesian grid using a two-pass Barnes filter ( Koch et al. 1983 ). The filter and grid parameters were chosen based on the data resolution δ at the range of the tornado. The KTLX data are oversampled every 0.5° in azimuth. The range from the radar to the tornado varied from 30.6 km at 1955:27 UTC (near the time of tornadogenesis; hereafter all times are UTC) to 11.9 km at 2033

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Erik N. Rasmussen
,
Jerry M. Straka
,
Robert Davies-Jones
,
Charles A. Doswell III
,
Frederick H. Carr
,
Michael D. Eilts
, and
Donald R. MacGorman

This paper describes the Verification of the Origins of Rotation in Tornadoes Experiment planned for 1994 and 1995 to evaluate a set of hypotheses pertaining to tornadogenesis and tornado dynamics. Observations of state variables will be obtained from five mobile mesonet vehicles, four mobile ballooning laboratories, three movie photography teams, portable Doppler radar teams, two in situ tornado instruments deployment teams, and the T-28 and National Atmospheric and Oceanic Administration P-3 aircraft. In addition, extensive use will be made of the new generation of observing systems, including the WSR-88D Doppler radars, demonstration wind profiler network, and National Weather Service rawinsondes.

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Robert D. Palmer
,
David Bodine
,
Matthew Kumjian
,
Boonleng Cheong
,
Guifu Zhang
,
Qing Cao
,
Howard B. Bluestein
,
Alexander Ryzhkov
,
Tian-You Yu
, and
Yadong Wang

A tornado outbreak occurred in central Oklahoma on 10 May 2010, including two tornadoes with enhanced Fujita scale ratings of 4 (EF-4). Tragically, three deaths were reported along with significant property damage. Several strong and violent tornadoes occurred near Norman, Oklahoma, which is a major hub for severe storms research and is arguably one of the best observed regions of the country with multiple Doppler radars operated by both the federal government and the University of Oklahoma (OU). One of the most recent additions to the radars in Norman is the high-resolution OU Polarimetric Radar for Innovations in Meteorology and Engineering (OU-PRIME). As the name implies, the radar is used as a platform for research and education in both science and engineering studies using polarimetric radar. To facilitate usage of the system by students and faculty, OU-PRIME was constructed adjacent to the National Weather Center building on the OU research campus. On 10 May 2010, several tornadoes formed near the campus while OU researchers were operating OU-PRIME in a sector scanning mode, providing polarimetric radar data with unprecedented resolution and quality. In this article, the environmental conditions leading to the 10 May 2010 outbreak will be described, an overview of OU-PRIME will be provided, and several examples of the data and possible applications will be summarized. These examples will highlight supercell polarimetric signatures during and after tornadogenesis, and they will describe how the polarimetric signatures are related to observations of reflectivity and velocity.

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Kevin R. Knupp
,
Todd A. Murphy
,
Timothy A. Coleman
,
Ryan A. Wade
,
Stephanie A. Mullins
,
Christopher J. Schultz
,
Elise V. Schultz
,
Lawrence Carey
,
Adam Sherrer
,
Eugene W. McCaul Jr.
,
Brian Carcione
,
Stephen Latimer
,
Andy Kula
,
Kevin Laws
,
Patrick T. Marsh
, and
Kim Klockow

tornadogenesis and tornado intensity change. Despite timely and accurate warnings by the National Weather Service (NWS) forecast offices, the number of fatalities (316) was high. The environment described in the following section was extremely conducive to the development of strong, long-track tornadoes. Although this dangerous situation was anticipated exceptionally well by the National Oceanic and Atmospheric Administration (NOAA) Storm Prediction Center (SPC), this paper does not focus on the forecasting

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Paul M. Markowski
,
Yvette P. Richardson
,
Scott J. Richardson
, and
Anders Petersson

matters much more than the buoyancy next to the surface ( Rotunno et al. 1988 ). In supercell thunderstorms, tornado formation is sensitive to the negative buoyancy and equivalent potential temperature of the rain-cooled, vorticity-rich air that emanates from downdrafts (e.g., Markowski and Richardson 2009 , 2014 ; Davies-Jones 2015 ), with tornadogenesis likelihood generally increasing as buoyancy and equivalent potential temperature increase within the rain-cooled, vorticity-rich air— at least

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James M. Kurdzo
,
Feng Nai
,
David J. Bodine
,
Timothy A. Bonin
,
Bradley Isom
,
Robert D. Palmer
,
Boon Leng Cheong
,
Javier Lujan
,
Andrew Mahre
, and
Andrew D. Byrd

-Doppler analysis of supercells and tornadoes (e.g., Wurman et al. 2007a , b ; Marquis et al. 2008 ; Wurman et al. 2010 ; Kosiba et al. 2013 ); polarimetric observations of convective storms (e.g., Frame et al. 2009 ; Tanamachi et al. 2012 ; Snyder et al. 2013 ; French et al. 2015a ; Houser et al. 2016 ); and volumetric scanning for analysis of tornadogenesis, tornadic dissipation and structure, and tornado damage (e.g., Wurman and Alexander 2005 ; French et al. 2013 ; Snyder and Bluestein 2014

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José Vicencio
,
Roberto Rondanelli
,
Diego Campos
,
Raúl Valenzuela
,
René Garreaud
,
Alejandra Reyes
,
Rodrigo Padilla
,
Ricardo Abarca
,
Camilo Barahona
,
Rodrigo Delgado
, and
Gabriela Nicora

values are associated with the propagation of the comma cloud structure eastward toward the continent, which is far less organized in WRF than in GOES infrared imagery. However, one can speculate that near-surface baroclinicity present at the surface front of the comma cloud structure could enhance the low-level shear by thermal wind balance and thereby favor tornadogenesis on 31 May. The absence of a similarly organized mesoscale structure on 30 May may explain that day’s relatively weaker SRH

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