Observational and Numerical Investigations of the Interaction of Synoptic Scale Weather Systems with the Orography of the Western United States

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9634191 Steenburgh It is well known that the Rocky Mountains have significant effects on cyclonic weather systems as they cross the mountains. The exact nature and reason for this impact, however, is not well understood. The primary objectives of this project are (1) to describe the interaction of extratropical cyclones and fronts with the complex orography of the western United States and (2) to document the evolution and dynamics of convective snowbands that form along the Wasatch Mountains of northern Utah. These orographic effects and features dominate the meteorology of the western United States and are responsible for life threatening and economically disruptive snowstorms, windstorms, and flash floods One component of the investigation will examine how synoptic systems, such as cyclones and fronts, are modified by their interaction with the Rocky Mountains. The project will develop regional climatologies of such interaction and perform a series of observational case studies utilizing a variety of mesoscale data sets. Numerical simulations utilizing an advanced mesoscale numerical model will be used extensively to supplement observational analyses and examine how orographic processes alter the structural evolution and dynamical balances of these systems. The second part of the investigation will describe the structure and dynamics of post-frontal convective snowbands that form along the Wasatch Mountains of Northern Utah. These features produce heavy snowfall in the Salt Lake City metropolitan area and appear to form as a result of the interaction of the synoptic flow with local orographic features, including the Great Salt Lake. Observations from a local mesoscale network and WSR-88D Doppler radar, coupled with numeri- cal simulations, will be used to document the evolution and dynamics of these snow- bands. In order to improve local forecasting, a climatology of post-frontal snowstorms along the Wasatch Front will also be devel oped. This project will advance the understanding and forecasting of terrain induced phenomena of the western United States. It will describe the interaction of cyclones and fronts with the complex orography of the region and evaluate the ability of numerical models to simulate mesoscale features produced by such interaction. ***