Severe Weather Session 2 Abstracts (Saturday)

11:15am - 11:30am // Tornado Debris Signatures Associated with Low-Topped Supercells in Southeast Texas on 31 October 2015 // Scott Overpeck // NWS Houston Galveston

On Halloween morning of 31 October 2015, 4 low topped supercells moved across the coastal counties of Brazoria, Galveston and SE Harris producing 11 tornadoes. Several of these supercells had tornado debris signatures associated with them. Multiple tornadoes were co-located with the debris radar signatures and produced EF-1 to EF-2 damage. The goal of this study is to document the environment in which the low topped supercells formed, the radar structure of the low topped supercells themselves, and the tornado debris signatures associated with the supercells. The environment supported the formation of low topped supercells with convective available potential energy (CAPE) of 1000 to 2000 J/kg, and 0 to 1 km storm relative helicity of 300 to 400 m2/s2. Radar imagery in close proximity to KHGX WSR-88D showed low topped supercell structures (updraft depth under 25,000 feet), and dual polarization products indicated debris signatures with low correlation coefficient co-located with a reflectivity maximum and velocity couplet. The debris signatures were limited in height due to the low topped nature of the supercells but also due to the small diameter of the tornadic circulation.

11:30am - 11:45am // Effects of Low-Level Vertical Wind Shear Orientation on Low-Level Rotation in Simulated Supercell Thunderstorms // Felicia Guarriello // Texas A&M University

Forecasting which supercells will form tornadoes is no easy task. While great strides have been made in this field over the last decade much remains unknown about tornadogenesis and maintenance. Of all the supercells with radar-detected mesocyclones, only about 25% go on to form tornadoes. With the advancement of numerical models, we have been able to analyze the importance of different environmental parameters that affect supercell tornadoes. Two particularly predictive parameters are the low-level (typically 0-1 km) vertical wind shear and lifting condensation level (LCL).

In this work, idealized soundings are used to simulate supercell thunderstorms using the CM1 model. These idealized soundings are manipulated to change the angle of the 0 – 500 m vertical wind shear vector with respect to the deep-layer hodograph in each simulation. Results from four cases will be presented: the control case, which has no shear in the lowest 500 m, the ‘0 degree’ shear case, ‘90 degree’ shear case, and ‘180 degree’ shear case. These cases will be compared to investigate how the angle of vertical shear orientation affects the developments of low-level rotation in supercell thunderstorms. In particular, it is expected that the sensitivity to the low-level shear is, in part, a product of the outflow position and characteristics in different shear regimes.

11:45am - 12:00am // West Texas Dust Storms and the Need for Improved Motorist Safety // Matthew Ziebell // NWS Lubbock

Extreme weather from the Texas Panhandle south to the Trans-Pecos region is often associated with a heightened frequency of severe thunderstorms and tornadoes. However, storm-related fatalities across these regions since 2004 reveal that more people have died from motor vehicle injuries associated with dust storms than from tornadoes, lightning and flooding combined. Regional awareness campaigns for motorist safety during dust storms are largely non-existent compared to similar campaigns for flooding and winter weather. For the National Weather Service offices and broadcast media that contend with dust storms, proposals are suggested to bolster motorist safety of these less sensational, yet significant weather events.