Enroute Icing

### Produced by The COMET® Program

### Step 1: Diagnosing Locations of Icing » Satellite Data » Overview

The satellite channels and products that are useful for determining icing potential include visible (VIS), shortwave IR (SW IR), longwave IR (LW IR), the Cloud Phase and Icing Potential RGB, and water vapor (WV).

Animated imagery from one or more of them lets you see the following:

- The evolution of the atmospheric flow up to the present, allowing the forecaster to make a “first forecast” projection into the future
- The past movement, current location, and possible future movement of moisture, clouds, and potential areas of icing
- The phase of cloud water (supercooled liquid, ice, or above freezing) at the cloud top

#### Question

Although each type of satellite imagery provides unique information about icing, they all share a common limitation. They cannot be used to determine:

a) The existence of supercooled water
b) Cloud top temperature
c) Nighttime cloudiness
d) Multiple cloud layers

The correct answer is d.

Visible and IR satellite data let us see the radiating or reflecting cloud top surface; cloud layers below are obscured. This means that forecasters must use additional tools to assess which flight levels have an icing risk within an area of moisture and clouds.

Option A is incorrect. Individual and multiple IR satellite channels can be used to find potential supercooled water. Option B is incorrect because the cloud top temperature can be determined from the amount of radiation emitted from the cloud top to the satellite. Finally, option C is incorrect because SW IR and LW IR satellite data can be used to find clouds at night.

Please make a selection.

On the next set of pages, we’ll discuss the characteristics that determine how each type of imagery is used in icing diagnosis, and the guidance that imagery can provide. Then we’ll look at the animations for the case. Note that we’ll only show imagery that’s practical for interpreting icing locations.

As you view the animations, look for areas of icing risk, how they are moving, and how they are changing in area coverage. Then on one culminating page, you’ll identify where icing is possible in the service area based on all of the imagery that you have seen.

An important caveat: Satellite imagery only tells part of the story. Forecast soundings, time height diagrams, and other analyses and forecast guidance are needed to refine icing flight levels and severity.