P61     Evaluation of a scale separation technique for assessing WRF forecasts of radar reflectivity.

Raby, John W., Brian P. Reen, Huaqing Cai, Jeffrey Smith, and Robert Dumais, Army Research Laboratory

The Army Weather Running Estimate–Nowcast (WRE–N), which utilizes the advanced research version of the Weather Research and Forecasting model (WRF-ARW) to generate nowcasts, was modified to improve hydrometeor forecasts in support of flight system testing at the Ronald Reagan Ballistic Missile Defense Test Site on Kwajalein Atoll. One of the modifications made was to enable assimilation of Kwajalein radar reflectivity data. An assessment of the WRE-N was needed to determine the value-added of this modification. Due to the difficulty of verifying forecasts of spatial fields of 1-km AGL reflectivity using traditional methods, a spatial verification technique called scale decomposition was evaluated for possible use because it has the capability to focus on reflectivity objects and assess the quality of the forecast structure in terms of the spatial scale of the error and intensity. It has been used for assessment of precipitation fields which are discontinuous in nature not unlike those of radar reflectivity. To apply this method of verification, the Wavelet-Stat tool of the NCAR Model Evaluation Tools was used. The results showed that this technique provided an assessment of model skill as a function of threshold value and spatial scale not achievable using other MET tools.