A comparison of WRF-RR and RUC forecasts of aircraft icing conditions

The Current and Forecast Icing Products (CIP and FIP, respectively) have used output from the Rapid Update Cycle (RUC) model to create icing diagnoses and forecasts since their inception. The RUC is scheduled to be replaced by the Rapid Refresh version of the Weather Research and Forecast (WRF-RR) model in 2010. Because model output is the only data source in FIP and plays a large role in CIP it is vital to compare and contrast how the models handle icing situations so that the algorithms can be adjusted accordingly.

An upgraded microphysics package has been added to the WRF-RR that explicitly predicts five hydrometeor species (rain, snow, graupel, cloud ice, and cloud water) along with number concentrations of rain and cloud ice. This double moment scheme should improve the model's hydrometeor forecasts, and its representation of icing conditions is important to the CIP and FIP development team.

The domain of the WRF-RR is also much larger than that of the RUC, including all of North America without a decrease in horizontal or vertical resolution. This allows the algorithms to be run on the same model over the CONUS and Alaska, something that wasn't possible before.

In order to gauge the effects of the WRF-RR on icing forecasts and diagnoses the algorithm developers examined and compared fields from both models during the 2009 icing season. Representative case studies highlighting similarities and differences in icing depiction between the models will be presented.