A near real-time satellite-based aircraft icing risk product for Alaska

The threat of ice buildup on aircraft surfaces from super-cooled liquid water (SLW) in clouds is one of the major safety concerns of the aviation community, especially for smaller, low-flying planes that are commonly used in Alaska. Using satellite data to detect areas of potential for aircraft icing is desirable since pilot reports (PIREPS) of icing tend to be subjective and their spatial coverage is limited mostly to areas near airports or airfields. A theoretically based flight-icing threat algorithm has been developed for application to current GOES-W and Terra and Aqua satellite image data. Across the high latitudes, it is a common occurrence for lower level clouds to be composed of SLW near their tops, which contributes to the high probability of detecting icing conditions when these clouds are in view of the satellite. The primary elements used to infer the flight icing threat are retrievals of the cloud phase, effective temperature, liquid water path and effective droplet size. The predominance of high solar zenith angles combined with snow and ice cover make the retrieval of these properties and icing risk difficult compared to mid-latitude locations. The satellite icing results are checked against PIREPS for consistency. Although limited due to high view angles and lower resolution, GOES-W provides the most timely satellite information, normally with a 10-20 minute latency. Terra and Aqua MODerate-resolution Imaging Spectroradiometer (MODIS) data is currently delayed by 1-3 hours with an improvement of 30 min to 1 hour of latency possible depending on image acquisition time. The satellite icing analyses and related cloud products will be provided to the NOAA National Weather Service's Alaska Aviation Weather Unit to assess their potential utility in daily operations. The data should help to provide a more accurate icing risk assessment over Alaska.