The Role of a Lid in the 31 May 1985 Tornado Outbreak
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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The Carlson-Ludlam Conceptual Model is useful for predicting severe convective outbreaks. Central to the entire model is the presence of an elevated mixed layer that caps and then helps focus the release of built-up latent instability in a concentrated area. An historical review of the models development and a thorough discussion of the concepts involved is presented. It is concluded that it is very successful at explaining many of the processes which produce severe convection. Subjective analysis necessary to use this model, however, is much too time consuming for operational forecasting. Therefore, a computer application is presented that objectively delineates lid involvement. The 31 May 1985 Tornado Outbreak occurred in the NE United States. Analysis reveals that there were four critical factors in the pre-storm environment responsible for the severity of the outbreak 1 the presence of a lid and the resulting build-up of a high wet-bulb potential temperature in the boundary layer, 2 readily available soil moisture, 3 underrunning, and 4 forced ascent associated with baroclinic forcing from a migrating short wave. Because vigorous short waves move across the NE United States several times each Spring and such outbreaks rarely occur, it is concluded that the lid was the most critical factor. Theses.