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Date added: 9.3.2015
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Quantitative precipitation forecasting is one of the greatest challenges currently facing the operational meteorological community. Modern short-term numerical forecasts only provide limited guidance owing to their coarse spatial and temporalMoreQuantitative precipitation forecasting is one of the greatest challenges currently facing the operational meteorological community. Modern short-term numerical forecasts only provide limited guidance owing to their coarse spatial and temporal resolution in comparison to the smaller scales needed to capture individual storms and their use of bulk-microphysical schemes. Further, convective events are often poorly resolved by the operational observing network, leading to poor analyses of the initial atmospheric state and subsequently poor forecasts. Presently, the Doppler radar network offers the only volumetric data suitable for more accurate assimilation on the storm scale. With polarimetric upgrades to the operational Doppler network underway, assimilating polarimetric radar observations will allow further improvement in the estimating the current atmospheric state. Further, more accurate retrieval of unobserved fields in real time, such as the low-level cold pool beneath supercell storms, would aid forecasters in current and future hazard assessment.-An existing ensemble Kalman filter data assimilation system developed at NSSL was upgraded to enable assimilation of real polarimetric radar observations through integration of an advanced dual-moment microphysical scheme and through development of forward operators for the polarimetric radar observables. The resulting differential reflectivity and specific differential phase operators have been shown to produce realistic polarimetric radar signatures for an observed supercell storm event. In addition, the system provided good retrieval of storm kinematic features that were enhanced through use of advanced microphysics and assimilation of polarimetric radar observations.-A detailed examination of the case study led to new insight into polarimetric field evolution associated with a significantly tornadic supercell thunderstorm. This included the identification of a specific differential phase foot and differential reflectivity shield as well as the first documentation focused on the relationship between polarimetric field evolution relative to surface gust front behavior. A strong but compact cold pool was found on the upshear side of the storm. However, an intriguing discovery was the lack of significant cooling at the surface within the forward flank downdraft region of the storm. Instead, there was an elevated cold pool along the forward storm flank that rested on a capping inversion layer. Comparison of the retrieved atmospheric state variables between the simple and advanced microphysical representation showed significant differences in spatial and temporal evolution, yet retrieved cold pool characteristics were qualitatively quite similar to one another and observations. This is related to the similar treatment of evaporation between the two microphysical schemes along the upshear side of the storm. Improving storm-scale analyses of convection via assimilation of polarimetric radar observations. by Glen Scott Romine
