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Article Type:
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Genesis of the Goshen County, Wyoming, Tornado on 5 June 2009 during VORTEX2

Karen Kosiba Center for Severe Weather Research, Boulder, Colorado

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Joshua Wurman Center for Severe Weather Research, Boulder, Colorado

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Yvette Richardson Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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Paul Markowski Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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Paul Robinson Center for Severe Weather Research, Boulder, Colorado

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James Marquis Department of Meteorology, The Pennsylvania State University, University Park, Pennsylvania

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Print Publication:
01 Apr 2013
DOI:
https://doi.org/10.1175/MWR-D-12-00056.1
Page(s):
1157–1181
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Abstract

The genesis of a strong and long-lived tornado observed during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) in Goshen County, Wyoming, on 5 June 2009 is studied. Mobile radar, mobile mesonet, rawinsonde, and photographic data are used to produce an integrated analysis of the evolution of the wind, precipitation, and thermodynamic fields in the parent supercell to deduce the processes that resulted in tornadogenesis. Several minutes prior to tornadogenesis, the rear-flank downdraft intensifies, and a secondary rear-flank downdraft forms and cyclonically wraps around the developing tornado. Kinematic and thermodynamic analyses suggest that horizontal vorticity created in the forward flank and hook echo is tilted and then stretched near the developing tornado. Tilting and stretching are enhanced in the developing low-level circulation as the secondary rear-flank downdraft develops, intensifies, and wraps around the circulation center. Shortly thereafter, the tornado forms. Tornadogenesis does not proceed steadily. Strengthening, weakening, and renewed intensification of the tornado are documented in photographic, reflectivity, Doppler velocity, and dual-Doppler fields and are associated with, and shortly follow, changes in the secondary rear-flank downdraft, convergence, location of the vortex relative to the updraft/downdraft couplet, tilting and stretching near and in the developing tornado, and the evolution of total circulation.

Corresponding author address: Dr. Karen Ann Kosiba, Center for Severe Weather Research, 1945 Vassar Circle, Boulder, CO 80305. E-mail: kakosiba@cswr.org

Abstract

The genesis of a strong and long-lived tornado observed during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) in Goshen County, Wyoming, on 5 June 2009 is studied. Mobile radar, mobile mesonet, rawinsonde, and photographic data are used to produce an integrated analysis of the evolution of the wind, precipitation, and thermodynamic fields in the parent supercell to deduce the processes that resulted in tornadogenesis. Several minutes prior to tornadogenesis, the rear-flank downdraft intensifies, and a secondary rear-flank downdraft forms and cyclonically wraps around the developing tornado. Kinematic and thermodynamic analyses suggest that horizontal vorticity created in the forward flank and hook echo is tilted and then stretched near the developing tornado. Tilting and stretching are enhanced in the developing low-level circulation as the secondary rear-flank downdraft develops, intensifies, and wraps around the circulation center. Shortly thereafter, the tornado forms. Tornadogenesis does not proceed steadily. Strengthening, weakening, and renewed intensification of the tornado are documented in photographic, reflectivity, Doppler velocity, and dual-Doppler fields and are associated with, and shortly follow, changes in the secondary rear-flank downdraft, convergence, location of the vortex relative to the updraft/downdraft couplet, tilting and stretching near and in the developing tornado, and the evolution of total circulation.

Corresponding author address: Dr. Karen Ann Kosiba, Center for Severe Weather Research, 1945 Vassar Circle, Boulder, CO 80305. E-mail: kakosiba@cswr.org
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