Wednesday, 6 October 2004
Following the passage of a cold front, an upslope stratiform cloud layer formed over northeastern Colorado. The clouds were mostly composed of supercooled liquid water at temperatures between -5oC and -12oC, resulting in moderate in-flight icing conditions in the Denver-Boulder-Greeley area. The event was captured well by both the NOAA Ground-based Remote Icing Detection System (GRIDS) Ka-band radar and the Current Icing Potential (CIP) in-flight icing product, and was sampled by the University of North Dakota's Citation research aircraft. GRIDS and CIP independently diagnosed the presence, altitude range, microphysical character and in-flight icing threat posed by these clouds, using different datasets. GRIDS integrates microwave radiometer data with Ka-band profiles to remotely measure the altitudes of the clouds and identify their phase, then combines this information with a temperature profile from the Rapid Update Cycle (RUC) model 1-hr forecast to determine if the liquid clouds pose an icing threat and if they contain supercooled large droplets (SLD). CIP uses GOES satellite data and surface observations of cloud cover and ceiling height to bound the clouds, then combines them with NEXRAD radar mosaic, surface observations of precipitation, observations of lightning from the national lightning detection network, recent pilot reports, and the RUC model's 3-hr forecasts of temperature, relative humidity, vertical velocity and supercooled-liquid water to estimate cloud presence, altitude, phase and potential for icing and SLD conditions. The GRIDS and CIP methods each have their strengths and weaknesses which led to good and poor aspects of their respective icing diagnoses for this event. In this paper, research aircraft data will be used to describe the microphysical characteristics of the icing clouds, and the GRIDS and CIP icing diagnoses will be compared and contrasted. Potential for the integration of these two techniques as a terminal-scale icing product will be discussed.
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