The Goshen County, Wyoming, supercell of 5 June 2009 intercepted by VORTEX2: Tornadogenesis phase

The genesis, intensification, and demise of an EF-2 tornado were observed on 5 June 2009 in Goshen County, WY during the VORTEX2 field campaign. Over 30 minutes of continuous fine-scale, dual-Doppler data were obtained in tandem with surface thermodynamic measurements. Dual-Doppler coverage commenced at 21:42 UTC and ended at 22:18 UTC. The tornado formed at approximately 21:56 UTC and lasted until approximately 22:34 UTC. A peak velocity of 62 m/s at 40 m AGL was measured at 22:14:50 UTC by DOW7. This research focuses on the genesis of the tornado, a period from approximately 21:48 UTC to 22:02 UTC. Preliminary analyses indicate a link between the development of a secondary gust front and tornado genesis. Prior to tornado inception, at 21:52 UTC, dual-Doppler analyses revealed the beginning of a wind surge in the rear-flank downdraft. This surge led to the development of a secondary gust front located behind the primary rear flank downdraft and adjacent to the developing tornadic circulation. Trajectory analysis indicated that the secondary surge was a predominate source of air for the tornadic circulation. Preliminary buoyancy retrievals coincident with tornado genesis suggest that the air behind the secondary rear flank gust front was positively buoyant. The source of this secondary surge as well as the kinematic and thermodynamic evolution of the secondary surge will be presented. Additionally, its link to tornado intensification will be discussed in the context of vorticity generation and/or transport.