Preprint, 15th Conf. on Numerical Weather Prediction and 19th Conf. on Weather Analysis and Forecasting SENSITIVITY OF MODEL THUNDERSTORMS TO MODIFICATIONS TO THE ENIRONMENTAL CONDITIONS BY A NEARBY THUNDERSTORM IN THE PREDICTION OF 2000 FORT WORTH TORNADO CASE

1It is generally recognized that the environmental buoyancy and vertical wind shear have important effect on the characteristics of convective storms. Parameters and indices, such as the bulk Richardson number (BRN) and environmental storm -relative helicity, have been commonly used in both research and operations to characterize the environmental properties important to thunderstorm development and evolution. Much of our understanding of the sensitivity of convective storms to these environment parameters has been derived from modeling studies that tested a varieties of, but often idealized, environmental conditions (e.g., Weisman and Klemp 1984, 1982; Eugene and Morris 2001). The real-world buoyancy and wind profiles are, however, often much more complex than can be adequately described by a few simple parameters. In fact, we found, through the study of a model-predicted real convective system, that a very small change in the midto-low level wind profile can produce very different behaviors of storms after their splitting. The case studied is that of the 2000 Fort Worth tornado. In this case, the initial development and evolution of the thunderstorm that spawned that Fort Worth tornado was well simulated. However, this storm’s evolution deviated from reality in the hour following the tornado outbreak due to its merging with a cell that was a spuriously intensified left mover from another storm to its front right. In reality, this left-mover dissipated quickly after initial splitting. This paper attempts to identify the cause of this incorrect behavior and in the process investigates the sensitivity of thunderstorms to small changes in the environmental conditions.