THE IMPORTANCE OF UNDERSTANDING MESOSCALE MODEL PARAMETERIZATION SCHEMES FOR WEATHER FORECASTING

A severe weather outbreak that occurred on 21-23 November 1992 in the southern United States is used to illustrate how an understanding of m odel parameterization schemes can help in the evaluation and utilizati on of mesoscale model output. Results from a mesoscale model simulatio n show that although the model accurately simulated many of the observ ed mesoscale features, there are several aspects of the model simulati on that are not perfect. Through an understanding of the model paramet erization schemes, these model imperfections are analyzed and found to have little effect on the overall skill of the model forecast in this case. Mesoscale model output also is used to provide guidance to eval uate the severe weather threat. By using the model output to produce h ourly calculations of convective available potential energy (CAFE) and storm relative environmental helicity (SREH), it is found that region s with positive CAFE, SREH greater than 150 m(2) s(-2), and model-prod uced convective rainfall correspond well with areas in which supercell thunderstorms developed. In addition, these parameters are highly var iable in both space and time, accentuating the need for continuous mon itoring in an operational environment and frequent model output times.