Thursday, 14 October 2010
Grand Mesa Ballroom ABC (Hyatt Regency Tech Center)
On the evening of 22 May 1987, a F4 tornado struck the town of Saragosa in southwest Texas, killing 30 people. This tornado was notable due in part to the post-assessment that systemic failures in the warning dissemination system contributed to the casualties and also due to the lack of major (F3 or greater) tornadoes in the historical record of the region. However, in the course of investigation of the 1987 tornado, it was discovered that several sources remarked that two significant tornadoes had previously hit the town. One source indicated that the town of Saragosa was "destroyed" by a tornado in June of 1938. According to this source, the town was dissolved in the 1940s and later re-established in a slightly different location. Another tornado reportedly hit the town on 23 July, 1964. As a result of heavy damage from this tornado, the town was moved again, although the source goes on to mention that the Saragosa post office was in the path of all three tornadoes. Neither the National Climate Data Center's Storm Data nor Tom Grazulis' book, Significant Tornadoes, contain any information on the 1938 or 1964 tornadoes.
The topography surrounding Saragosa varies from mountainous terrain to the west and south, to the lower elevation and smoother terrain of the Pecos River valley to the north and east. There is ample anecdotal evidence among operational meteorologists that a local maximum in thunderstorm activity occurs in this region. This maximum is commonly attributed to the influence of the local terrain. Although not confirmed, the hypothesis is that the terrain orientation results in: 1) upslope flow which in turn produces upward vertical motion; and 2) the formation of a convergence vorticity zone. In this case, these same factors may also produce a more favorable environment for tornadogenesis.
This study will present a detailed meteorological analysis of the 1987 tornado. High resolution simulations using the Weather Research and Forecasting (WRF) model were performed to evaluate whether the environment was supportive of tornadic thunderstorms for the 1987 and 1964 cases with an emphasis the possible enhancement of tornadic potential due to the local topography.
- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner