Enroute Icing

### Produced by The COMET® Program

### Step 1: Diagnosing Locations of Icing » NEXRAD Radar » Description

Radar shows the location and intensity of precipitation. Where precipitation echoes exist, there is enough condensed cloud water to produce precipitation. Below-freezing air below the melting layer signals a risk for moderate or greater clear or mixed icing if the precipitation has not had a chance to fully refreeze.

Usually, further diagnosis is needed to determine the icing risk. However, radar can be used to find the 0°C isotherm if there is a melting layer aloft where snow transitions to rain. The melting layer shows up as a “bright band” of high-reflectivity melting snow marking the 0°C isotherm. Below-freezing air close to the surface signals a risk for moderate or greater clear or mixed icing. This sample radar from another case has bright banding.

There are many advantages to using radar. It provides clear depictions of precipitation areas and is useful in corroborating freezing precipitation observations (METARs). In addition, the bright banding can be used to locate the precipitation melting level.

But radar has limitations. It lacks information on temperature structure beyond bright banding and cannot locate supercooled moist layers without bright banding. An entire supercooled layer can be “hidden” unless you use other sources for vertical temperature and moisture information, such as a Skew-T.