3B.3 Genesis and maintenance of a long-track EF5 tornado embedded within a simulated supercell

Monday, 3 November 2014: 2:00 PM
University (Madison Concourse Hotel)
Leigh Orf, Central Michigan University, Mount Pleasant, MI; and R. B. Wilhelmson, L. J. Wicker, B. D. Lee, and C. A. Finley

The "Calumet-El Reno-Piedmont-Guthrie" tornado swept through the northern outskirts of metropolitan Oklahoma City on May 25, 2011. The tornado, rated EF5 based upon University of Oklahoma mobile Doppler radar, left a damage path of 65 miles. We present results from an ultra-high-resolution (30 meter grid spacing) supercell simulation generated on the Blue Waters supercomputer by the CM1 numerical model. The model is initialized with a sounding generated from a 1 hour RUC forecast, taken from the location of the right flank of the observed storm. The simulated supercell is strong and long-lived, and produces a long-track (65 miles by 3 hours model time) EF5 tornado. The simulated storm bears some strong similarities to the observed storm including track length, direction and intensity. To the best of our knowledge, this is the first time a supercell producing a long-track EF5 tornado has ever been simulated. The simulated tornado reaches EF5 strength approximately 98 minutes into the model simulation. The tornado maximum surface winds remain consistently at or well above EF5 strength for a continuous period of 40 minutes. Maximum instantaneous ground-relative surface winds exceeding 140 m/s occur in the simulation. The vortex that ultimately becomes the tornado precedes tornadogenesis by nearly ten minutes time. During this ten minute period, the vortex strengthens as several shallow vortices formed along the forward flank gust front (FFGF) strengthen as they move rearward along the FFGF and merge with the nascent tornado. Tilting of baroclinically generated streamwise horizontal vorticity along the FFGF into the vertical by the updraft appears to play an important role in strengthening and maintaining cyclonic circulation aloft including that of the tornado cyclone. Forward-integrated trajectories indicate that high-momentum air within the tornado itself originates from very near the ground, and contains air from the cold pool in both the rear and forward flank of the storm, as well as environmental air ahead of the storm. The tornado at its strongest takes on a two-celled structure with a downdraft in the tornado eye, and exhibits vortex breakdown aloft.

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