Thursday, 6 November 2014
Capitol Ballroom AB (Madison Concourse Hotel)
Convection over statically stable boundary layers (i.e., elevated convection) occurs over much of the United States, producing heavy rainfall, hail, and occasionally severe surface winds. Much of the current literature on elevated convective storms concerns those of a linear morphology; studies of elevated supercells are largely absent. Elevated supercells present an operational challenge because they look similar to surface-based storms on radar, which can lead forecasters to issue warnings for severe winds and tornadoes that are not likely to verify. Both tornadoes and severe winds do seem to occur in a handful of elevated supercells, with the reasons behind their formation currently unknown. To further understand the governing dynamics, an elevated supercell case from the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) on 6 May 2010 is being investigated. VORTEX2 measurements provide an unprecedented dataset that includes radar data from Doppler-on-Wheels (DOW) and Shared Mobile Atmospheric Research and Teaching Radar (SMART-R) mobile radars and surface mobile mesonets. Observations show that the supercell that formed over a stable inversion and was decoupled from the surface. As a result of the decoupling, the surface cold pool was fueled without the help of mid-level air. Waves were also present in the environment. Additionally, idealized modeling using a sounding from this case was undertaken to further understand the structure and maintenance of this supercell as well as its severe weather potential. Results show that the anticyclonic hook echo is the product of strong negative vorticity in the rear-flank influencing hydrometeors during descent. The supercell's own dynamic lifting, paired with waves, maintain the main updraft using instability from the mid-levels. Strong surface winds did occur near the storm; however, mid-level downdrafts were not the cause as air from aloft loses its negative buoyancy in the inversion.
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