Use of High Resolution Field Data to Improve Model Microphysics and Investigate Orographic Precipitation Processes

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Accurate prediction of precipitation amounts (quantitative precipitation forecasting; QFP) is a difficult forecasting problem, but one that has a potentially high societal benefit. For this reason, the U.S. Weather Research Program has identified QPF as a high priority research area. The primary objectives of this project are to use high-resolution field observations to verify and improve the numerical representation of microphysics in mesoscale models and to document the three-dimensional structures and physical mechanisms of orographic precipitation.This research is motivated by the fact that QPF continues to be a difficult problem for numerical weather prediction models. Recent studies have suggested that increasing horizontal resolution to a few kilometers often does not lead to more accurate precipitation forecasts, even over areas of complex terrain such as the Pacific Northwest, where the mesoscale flow is highly deterministic and the precipitation is mostly stratiform. There is growing evidence suggesting that these problems are associated with deficiencies in model microphysics. Therefore, a major objective of this project is to use remotely sensed (radar) observations, in situ aircraft data, and ground measurements to verify and improve the bulk microphysical schemes in mesoscale models. In order to evaluate the model microphysics for different types of environmental conditions, this study will utilize field data from IPEX (Intermountain Precipitation EXperiment) over northeast Utah, PACJET (PACific Landfalling JETs) along the West Coast, and IMPROVE (Improvement of Microphysical PaRameterization through Observational Verification Experiment) over the Oregon Cascades.These field studies also provide an opportunity to study the detailed three-dimensional structures and physical mechanisms associated with orographic precipitation. For example, radar and in situ aircraft data will illustrate how the orographic cloud and microphysics are modified by blocking and mountain wave dynamics as well as latent heating/cooling within the cloud. These observational results will also be compared and augmented with high-resolution model simulations. Overall, understanding these sensitivities combined with improvements to the bulk microphysical schemes will help improve quantitative precipitation forecasting.