RUI: Precipitation Regimes Associated with Inverted Troughs

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9610356 Weisman Cyclones and frontal systems associated with inverted troughs have been found to be a frequent occurrence in the Central United States. A 6-year survey has shown 247 cases involving inverted troughs in the Central U.S. between the lee of the Rockies and the Mississippi River. This relatively frequent phenomenon is not accounted for in current polar front models. The goal of this project is to build upon prior research by determining the dynamic support for the precipitation distribution during inverted trough cases. The preliminary survey of inverted trough cases has determined that there are two primary precipitation distributions in cases involving an inverted trough: 1) most of the precipitation falls downstream of the trough in the older, modified polar air mass (Ahead cases) and 2) most of the precipitation falls upstream of the trough in the fresh supply of arctic air (Behind cases). In the 6-year survey of inverted troughs, 42% of the cases fell into the Ahead category, while only 9% fell into the Behind category, but several of the Behind cases were major blizzards. The remaining cases were a combination of the two categories. This project will involve compositing the Ahead and Behind cases for comparison of forcing mechanisms. Calculations of lifting mechanisms such as warm advection, frontogenesis, and quasi-geostrophic forcing will be performed for each composite in order to identify the relative importance of these processes in the two categories and to enable comparisons between the two precipitation signals. It is hoped that the results of this project will provide a conceptual model for forecasters to use in real time to improve rain and snow forecasting during inverted trough cases. ***