Clouds: The radar reflectivity data is used to define the boundaries of cloud layers by defining cloud as being at least 1 dBz above the range–corrected noise floor for at least 200m (the range gate spacing for this system is 30 m). A 5–min smoothing was applied. The lower boundary of the lowest cloud layer is refined using the ceilometer data to correct for precipitation effects or for the close–range radar blind spot. Once the cloud boundaries have been defined, the radiometer's temperature profile is used to determine the portion of the clouds that are <0°C, for later evaluation of icing hazard altitudes.

Liquid water distribution: Total integrated liquid water is divided among the cloud layers using height and temperature criteria (explain). The vertical distribution within each cloud layer is determined independently by distributing the liquid according to four criteria:

• Wedge: many clouds with relatively warm tops (>∼ –10C) and no ice crystals have a wedge–shaped liquid water profile that increases somewhat linearly to a maximum at or just below cloud top
• Uniform: works as a first guess when the composition of the cloud is unknown
• Reflectivity–weighted: when reflectivity is high enough to suggest snow or rain, assume that the more reflectors, the fewer cloud drops and thus less liquid water content – weigh liquid water content inversely with radar reflectivity
• Temperature weighted: if the cloud is cold (>∼ –10C), significant ice crystal production is expected with more ice at colder temperatures so the liquid water content is weighted inversely with temperature

The four profiles are combined based on our clues from the instruments as to the composition of the cloud: all water, mixed–phase or glaciated. These decisions are made based on the temperature and reflectivity information for each cloud layer.

Icing: Icing hazard is defined by the liquid water content at any level with temperature <0°C. The scale is from a study (Politovich, 2001) defining icing severity by accretion rate on an airframe.

Display: The display is designed for real–time monitoring of both the icing condition and instrument status. The display includes the final icing hazard depiction as well as the source data (radiometer–measured integrated liquid water content, temperature profile, radar reflectivity), intermediate derived products (isotherms for selected temperatures, cloud base height, cloud mask, liquid water content) and instrument status (red or green lines). Controls for displaying real–time or archived data are also available.