The CIP inflight icing severity algorithm

Predicting the expected severity level of inflight icing conditions is a difficult task for the human forcaster. NCAR recently incorporated severity into their automated Current Icing Potential (CIP) algorithm. Severity is a combination of the atmospheric condition and the aircraft’s response as it encounters that condition. Additionally, when a pilot reports icing in a voice pilot report (PIREP), that information is interpreted by the pilot in a somewhat subjective manner. The CIP severity algorithm attempts to reconcile these often conflicting sources of information.

CIP uses fuzzy logic techniques to combine information from the Rapid Update Cycle (RUC) numerical weather model with observations from satellites, NEXRADs, METARS, the national lightning detection network and PIREPs. CIP produces an hourly, three-dimensional gridded icing and supercooled large drop (SLD) potential field which is the starting point for the severity algorithm. Light icing severity is assumed for any grid point with potential >0.05 (on a 0-1 scale), with moderate assumed for locations with SLD conditions, including deep convection. From there, the icing severity is adjusted using RUC forecasts of liquid water content, vertical velocity, as well as the severity reported in recent nearby PIREPs. The output is produced on the same grid as the icing potential. More details of the algorithm and some examples of its application will be presented, as well as ideas for future enhancements. Verification of the algorithm will be discussed in a separate paper.