Orographic Precipitation Processes over the Wasatch Mountains during the Intermountain Precipitation Experiment (IPEX)

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Improvement in quantitative-precipitation forecasts over the western United States requires advances in several areas including the understanding of dynamical and microphysical processes during orographic precipitation events and the numerical simulation and parameterization of orographically-induced circulations and precipitation microphysics. The interaction between terrain-induced flow fields and orographic precipitation processes remains poorly understood, and the measurement and prediction of orographic precipitation is a major scientific challenge. This is particularly true over narrow and steeply sloped mountain ranges, such as those of the Intermountain West, where the quantitative precipitation forecast skill of operational numerical weather prediction models is substantially lower than in other regions of the United States.The primary objectives of the research are (1) to advance fundamental knowledge of orographic precipitation processes over the Intermountain West, with an emphasis on the Wasatch Mountains of northern Utah; (2) to validate and improve mesoscale model performance and quantitative precipitation forecasts over regions of complex terrain. The project will utilize data collected during the Intermountain Precipitation Experiment (IPEX), a major field program held in northern Utah during February 2000. Specialized data sets collected during IPEX include airborne Doppler-radar and microphysical observations, ground-based radar observations collected by two mobile Doppler radars, and high resolution surface and upper-air observations. These data sets will be used to examine factors controlling the distribution of precipitation across the Wasatch Mountains, including windward enhancement by upstream blocking effects and the influence of mountain-wave structure on lee-side spillover.These objectives are directly related to the quantitative-precipitation forecasting focus of the U.S. Weather Research Program (USWRP). Results from the project will also have positive scientific and socio-economic benefits for the West, including Salt Lake City, host of the 2002 Winter Olympics. Educational benefits include the participation of graduate students from the University of Utah and the use of project data sets and findings for classroom instruction.