A Morphing-based Technique for the Verification of Ensemble Forecasts of Precipitation Events Associated with Winter Storms

This paper employs a new morphing-based technique for the verification of operational ensemble forecasts of precipitation events associated with winter storms. The technique, which uses an iterative approach to match the forecast and verifying precipitation features, is applied to forecasts of the named storms of the 2014/2015 and 2015/2016 winter storm seasons. The predictability of the related precipitation events and the performance of the ensembles are assessed based on three characteristics of the precipitation fields: position, amplitude, and structure. The operational forecasts used for our investigation are global ensemble forecasts from the National Centers for Environmental Prediction (NCEP), while the verifying analyses are operational precipitation analyses from the European Centre for Medium Range Forecasts (ECMWF). At short forecast times, the forecasts are found to underestimate the uncertainty for all three characteristics, but at around forecast time 120-h, the uncertainty and its ensemble-based prediction starts to saturate quickly at similar levels. In addition, the magnitude of the systematic errors in the prediction of the uncertainty increases with increasing forecast time.