IceThreat: using icing algorithm output to propose AIRMET regions

AIRMETs (Airmen's Meteorological Information) for aircraft icing are produced at the Aviation Weather Center (AWC) and represent the official forecast of in-flight icing conditions. The Current and Forecast Icing Products (CIP and FIP) are also run operationally at the AWC. They are used as guidance for the forecasters and supplementary icing information for pilots and dispatchers. A common complaint of forecasters at the AWC who use the icing algorithms as guidance is that the output provides little assistance in creating the AIRMETs. The AIRMET provides a six-hour forecast of icing conditions and must account for movement and evolution of the icing conditions during that time. The CIP and FIP provide gridded icing snapshots that are valid for one hour and evolve the conditions as observations change and model forecasts update.

This paper will describe IceThreat, a program developed at NCAR to use output from the automated icing algorithms to create a suggested icing AIRMET that could then be edited and issued by AWC forecasters. The method uses the icing probability and severity fields to locate areas with a high probability of moderate or greater icing. It then combines these hazardous regions into “clumps”, for which a floor and ceiling are calculated. If other clumps are found within a certain distance from each other then they are merged and a boundary is drawn around them. The final product is a list of corner points with a floor and ceiling that can be plotted and used by forecasters as an initial estimate of AIRMET boundaries. IceThreat will be installed in the Aviation Weather Testbed at AWC for testing and evaluation by forecasters there. This paper will describe the methods used by IceThreat for determining the suggested AIRMET regions and how the user can customize the program. It will also present examples of its use and how the output compares with official AIRMETs and pilot reports of icing.