Enroute Icing

### Produced by The COMET® Program

### Step 2: Make a First Forecast » Make the First Forecast

#### Question 1

Now we'll describe the icing conditions as of 13 UTC 26 February 2011. In this first question, you'll identify areas of icing, then in question 2 you'll identify the flight levels and intensity for those areas.

Use the pen to enclose areas of icing at 13 UTC.

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To identify the area coverage, we used the area with a 50% or greater probability of experiencing icing from the 13 UTC analysis CIP Probability of Icing chart.

#### Question 2

(Use the selection boxes to choose the answers that best complete the statement.)

As of 13 UTC 26 February 2011, icing conditions were expected
, with
intensity.
Icing conditions were expected from the surface to FL100, with moderate intensity.

To identify the icing levels, we used the PIREPs, layer mean maps, and cross-sections, which all showed the top of the moist sub-freezing layer at about 700 hPa, or about FL100. The bottom of the icing level is at the surface over the service area. Severity was obtained from the CIP icing severity composite.

#### Question 3

Based on the initial temperature, moisture, and winds, how do you expect the icing area(s) to move over the next 8 hours? Specifically, where will the forecast forward edge of the icing extent be on 26 February at 15, 18, and 21 UTC over the service area?

Draw the forecast forward edge of the icing areas using the red pen for 15 UTC, the blue pen for 18 UTC, and the gray pen for 21 UTC.

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The graphic shows a first forecast consistent with quasi-steady state atmospheric flow, with a steady advance of the initial icing area from the west-southwest to the east-northeast at 15, 18, and 21 UTC. Maintaining the icing layer from the surface to FL100 is also consistent with a steady state situation.

#### Question 4

Now enclose any areas that may be affected by SLD at 15 and 21 UTC.

Use the green pen to enclose any areas affected by SLD at 15 UTC and the gold pen for any areas affected at 21 UTC.

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The CIP indicates that SLDs in northeast Kansas and northwest Missouri are about to be advected into the service area at 13 UTC. For a steady state flow regime, we draw a yellow curved line in the southwest service area straddling the Mississippi River in southeastmost Iowa, and west-central Illinois. By 21 UTC, the SLD area should reach across the entire southern 1/3 of the service area to southwestermost Michigan and northwest Indiana. This would include the Chicago O'Hare airport.

#### Question 5

Use the selection boxes to choose the answers that best complete each statement.

At 15 UTC, moderate to severe icing was expected in the
part of the Chicago CWSU service area from
to
with light to moderate icing over the
portion of the service area.

At 15 UTC, moderate to severe icing was expected in the southwest part of the Chicago CWSU service area from the surface to FL100 with light to moderate icing over the western portion of the service area.

By 21 UTC, moderate to severe icing was expected in
and light to moderate icing was expected over
from
to
.

By 21 UTC, moderate to severe icing was expected in northern Indiana and light to moderate icing was expected over Wisconsin from the surface to FL100.

Below is the final first forecast graphic with the 13 UTC 26 February 2011 icing locations enclosed by black; the forecast forward edge of icing indicated by shading enclosed by dashed lines; flight levels indicated by text; and the advance of SLD and possible moderate to severe icing shown with shading enclosed by solid lines. Areas with moderate to severe icing expected are affected by the east-northeast movement of the SLD area originally to the immediate southwest of the service area. The southeastern third of the service area was expected to be affected by 21 UTC. Other areas of the service area were expected to have light to moderate icing moving north and east from Iowa into northwest Illinois, southern Wisconsin and southern Lake Michigan by 21 UTC.

Icing FLs are determined from the initial PIREPs/AIREPs, cross-sections, and plan view maps of mean layer temperature, RH, and vertical motion. The initial icing area is established using all of the satellite, analysis, and other observation data available, which were consistent with the Current Icing Products. The forward edge of icing and of expected SLD are predicted assuming steady-state advection of conditions from west-southwest to east-northeast during the first forecast period.

This completes Step 2. We're ready for the final step, where we adjust the first forecast, if necessary, based on model guidance.