18-dBZ Echo Top: An assessment of how this product may influence decision making in the NAS

The 18-dBZ echo top (ETP18) is a product that has existed since the WSR-57 era. It’s long-standing existence in the aviation community makes it somewhat of an intractable decision point. Yet, ETP18 suffers from some profound artifacts that may make its consistent application to decision support dubious. For example, ETP18 can be vulnerable to both cone-of-silence and beam broadening artifacts. These have the opposing impacts of causing ETP18 to be underestimated or overestimated, depending on the distance between the storm and the radar. Eliminating these artifacts from mosaics is quite challenging and different methods of creating mosaics may result in radically different assumptions about the depth of storms. An intercomparison of 2 methods of generating ETP18 within the MRMS system as they apply to the production of Convective SIGMETs (C-SIGs) and verification of the TCF is performed. Differences in maximum storm tops within C-SIG polygons can exceed 20 kft. Polygons of ETP18 greater than 25 kft are created using either method and intercompared to evaluate how ETP18 production may impact the TCF verification. The two methods have consistently different foot prints, percent coverage, and maximum storm tops. Differences are significant enough to impact the apparent performance of the TCF.