National Severe Storms Laboratory

A New Vision of the Multi-Scale Processes that Organize the Pre-Tornadic Environment

Dr. Mike Kaplan
Desert Research Institute (DRI)
Reno, Nevada

17 April 2014, 10:00 AM - 11:30 AM

National Weather Center, Room 1350
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Extensive research on the downstream effects of the atmospheric adjustments during a variety of western U.S. dust storms is described. The research indicates the potential impact of these adjustments on the downstream pre-tornadic environment. The focal point will be on the upstream dynamical and thermodynamical processes over the southwestern high plateau of the U.S. and the Sierra Madre Mountains during dust storm development. Specifically we will focus on how these processes organize an environment favorable for the concentration of isentropic potential vorticity (IPV) above and near the downstream dryline over Oklahoma. This research indicates several unique subsynoptic processes in the upstream pre-tornadic environment that phase and couple in a synergistic manner. First, an adjustment to thermal wind imbalance occurs as an upstream synoptic scale jet streak interacts with elevated mixed layers. Second, the mass adjustment to thermal wind imbalance results in multiple mid-tropospheric mesoscale jet streaks. Third, each mesoscale jet streak is coupled to an incipient mesoscale cold pool aloft and creates a mid-tropospheric streamer or banner of IPV as subcritical flow separation occurs above the elevated mixed layer. Fourth, the mid-tropospheric IPV streamers, their accompanying mesoscale jets and mid-tropospheric cold pools all propagate downstream over and ahead of the dryline. This creates an environment of enhanced cape, vertical wind shear and IPV during proximity to supercell genesis. More specifically, the IPV streamers in the mid-troposphere couple to the boundary layer IPV features ahead of the dryline close to the time of supercell genesis. Numerical simulations and observations will be presented of these processes for the 10 May 2010 Oklahoma tornado outbreak case study.

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