Analysis of level II doppler radar data for an episode of severe weather on 25-26 May 1994

This thesis is an investigation of a severe weather outbreak on the High Plains of West Texas on 25-26 May 1994. Archive Level II data was analyzed from the Lubbock, Texas (KLBB) Doppler radar for the period 1548 GMT on 25 May through 0511 GMT on 27 May 1994. Reflectivity and velocity data from this time period were read from 8-mm data cartridges using the WVS (WSR-88D Visualization System) program. The radar data was then used to determine the structure, strength, and movement of storms over the two-day period.

Particular emphasis of this study was placed on reflectivity and velocity data for the Northfield tornadic supercell (25 May) and the Reese non-tornadic supercell (26 May). The two storms developed in markedly different weather scenarios, with the Northfield storm producing two tornadoes and the Reese storm generating significant quantities of large hail. The Northfield supercell formed ahead of a cold front in a moisture convergence maximum between Amarillo and Childress. In contrast, the Reese supercell developed on an 850-mb boundary (cold front) in a region of upslope flow ahead of an advancing squall line. Outflow from storms that produced significant downburst damage in Lubbock County interacted with the Northfield supercell just prior to tornado formation. This outflow provided a source of low-level speed and directional shear for tornado production in the Northfield storm. The Reese supercell lacked a low-level source of rotation which is why no tornadoes or a mesocyclone was observed in the Level II data.

The movement of supercell thunderstorms on 25 May was controlled by strong southwesterly steering currents at the mid- and upper-levels of the atmosphere. In contrast, the three supercells of 26 May lacked significant steering currents in the mid-levels. This most likely explains why outflow boundaries controlled the movement of the three supercells. No outflow boundaries were detected near the Reese supercell after 2300 GMT which explains why the storm remained quasi-stationary for over three hours.