Mesoscale Modeling of Precipitation in Coastal Regions of Complex Orography

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9612876 Mass The U.S. Weather Research Program (USWRP) is an interagency activity designed to perform and implement the research necessary to improve the delivery of weather services to the nation. Under this Program, the National Science Foundation and the National Oceanic and Atmospheric Administration (NOAA) are jointly evaluating and supporting weather research of high priority to the USWRP. The distribution of precipitation along the west coast of North America is greatly influenced by the orography of the region, resulting in a complex pattern of enhancement on the windward sides of mountains and precipitation shadows to their lee. The importance of orographic modulation of coastal zone precipitation has been highlighted recently by a series of major flooding events in northern California and the Pacific Northwest that have resulted in losses in the billions of dollars and several deaths The objective of this proposal is to evaluate the potential of high-resolution regional atmospheric models for diagnosing and predicting orographically modulated precipitation along the mountainous coastal zone of western North America. Although current operational weather prediction models lack the resolution to correctly forecast orographic precipitation, a growing collection of regional model simulations suggests that with sufficient resolution, precipitation can be predicted realistically in coastal regions of complex terrain. If successful, high resolution modeling would offer improved precipitation forecasts and coupling their output to hydrological models could lead to more accurate prediction of stream flow, river stages, and flooding. This research effort will evaluate the performance of a high-resolution mesoscale model for a range of heavy precipitation/flooding events along the orographic west coast of North America. As part of this evaluation, experiments will be made to determine the resolution, model physics, and data assimilation methods r equired for producing the best possible regional model performance for coastal precipitation/flooding events. The model will be run both in real time to evaluate the long-term precipitation skill of the model at moderate (~10-15 km) resolution and for a series of retrospective case studies at very high resolution (down to 1-3 km horizontal resolution). These case studies will include California and Pacific Northwest heavy precipitation/flooding events and at least one case for southeastern Alaska. In addition to evaluating and improving the ability of high resolution atmospheric models to forecast orographic precipitation, this effort will also involve interfacing the model's precipitation, temperature, and wind fields with a watershed hydrological model. Such model coupling has the potential to greatly improve short- term forecasts of river height and flooding. Finally, this project will promote active interaction between the University of Washington scientists and National Weather Service forecasts offices in California, Oregon, Washington, and Alaska. ***