P73 A novel weather-regimes objective verification of daily precipitation

This work analyzes the capability of the Weather Research and Forecasting (WRF) model with four-dimensional data-assimilation (WRF-FDDA) to reproduce daily precipitation over the south-eastern Mediterranean. The WRF-FDDA system was used to dynamically downscale global Climate Forecast System (CFS) reanalysis with continuous assimilation of conventional and unconventional meteorological observations. Winter precipitation (December-January-February, DJF) in 7 seasons, including an extreme dry and an extreme wet season in the past decades were generated at a 2-km spatial resolution.

Correct reproduction of the DJF precipitation is conditioned to correct simulation of extra-tropical cyclones. Alpert, et al. (2004) classified the daily synoptic-scale flow in the region into 19 weather regimes, seven of which are identified with extra-tropical cyclones. The cyclone classes differ in the geographic location and depth of the cyclone minima. We developed an objective weather-regimes verification approach to assess the skill of the system in simulating the precipitation resulting from the different types of cyclones. We compared between rain-gauges and model mean-daily precipitation associated with the various extra-tropical cyclone types at five hydrological basins. The comparison shows that while positive model biases are larger at coastal-flat areas under shallow-cyclonic conditions, deep-cyclonic conditions lead to more significant positive biases in complex-terrain regions. The weather-regimes verification information can be further used in a post-processing calibration procedure.