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University of Illinois: "Improving operational forecasting of Midwestern severe weather"

Final Report

This Cooperative Project had as its primary goal the improvement of operational forecasting of midwestern severe weather. The first part of the research involved the study of severe convective storms common in late spring, summer and early fall. The specific objectives were to: a) document the spatial, temporal, and climatological features of High Precipitation (HP) supercell storms in the Midwest, b) identify unique HP storm structure in reflectivity and Doppler velocity patterns, c) examine the evolution of multiple mesocyclones during the life span of an HP storm, and d) develop the conceptual models necessary for application in NWS Forecast Offices. The second part of the research involved severe cyclonic storms occurring during the winter. Tasks being conducted include (a) developing case studies of specific severe winter storms that were misforecast, and (b) examining how radar and profiler data could have been used to improve the forecasting and nowcasting of these cases.

Summer Storm Research: Research into severe summer storms in the Mid-Mississippi Valley Region (MMVR) was partially motivated by the fact that current conceptual models of supercells and operational forecasting practices for use with the WSR-88D radar and other modernized observation systems were developed from observations taken outside the MMVR. This raises questions about the applicability and representativeness of the current models. Efforts under this task had three major thrusts: (1) to review and compile a list of existing conceptual models, (2) to conduct observational studies that may alter existing conceptual models, and (3) to apply operationally accepted, revised and/or newly developed conceptual models.

Four observational studies developed during the project showed both similarities and differences to the classic models developed from southern Great Plains observations and the High-Precipitation models developed for the MMVR from WSR-57D and 74C radar observations. One important finding was that mesoscyclone evolution that occurred in cool-season, strong-dynamic environments differed from the “classic models” in that, for example, in the early stage, circulations formed at a lower altitude than observed in the high plains model. Another finding was that supercell reflectivity evolution was surprisingly similar to that developed for the southern high plains in that cells tended to move along a preexisting source of baroclinically generated horizontal vorticity.

A number of additional cases are still under investigation and it is expected that the findings will be reported in a journal article.

Winter Storm Research: Three case studies were developed to examine the problem of forecasting intense winter weather that occurs on the mesoscale in the midwestern United States. The first study concerned the role of mesoscale gravity waves in initiating precipitation in winter cyclones. The second study involved an extreme freezing rain event that produced extensive damage in east-central Illinois. The third case was a snow storm which was misforecast by two days. The analyses from the first two cases have been presented in journal articles; a paper describing the third case study is in preparation.