Evaluation of the baseline NEXRAD icing hazard project
September 17, 2015
MIT Lincoln Laboratory has developed an icing hazard product that is now operational throughout the NEXRAD network. This initial version of the Icing Hazard Levels (IHL) algorithm is predicated on the presence of graupel as determined by the NEXRAD Hydrometeor Classification Algorithm (HCA). Graupel indicates that rime accretion on ice crystal aggregates is present. It is inferred that the riming process occurs at the altitude that HCA reports graupel as well as to some vertical depth above. To capture some of that depth, temperature and relative humidity interest fields are computed from meteorological model data based on the technique used in the National Center for Atmospheric Research's Current Icing Potential Product and utilized within IHL as warranted. A critical aspect of the IHL development has focused on the verification of the presence of icing. Two methods are used. For the first, pilot reports of icing (PIREPs) are used to score the performance of IHL. Since PIREPs are provided with inherent time and space uncertainties, a buffer of influence is associated with each PIREP when scoring IHL. Results show the IHL as configured is an effective indicator of a potential icing hazard when HCA graupel classifications are present. Results also show the importance of radar volume coverage pattern selection in detecting weak returns in winter weather. For the second, in situ icing missions were performed within range of a dual pol NEXRAD to provide quantitative data to identify the presence of supercooled liquid water. Comparisons of in situ data to HCA classifications show that HCA graupel indications do not fully expose the icing hazard and these findings are being used to direct future attention of IHL development. This paper will describe the verification method and performance assessment of the IHL initial capability.