Enroute Icing

### Produced by The COMET® Program

### Step 3: Use NWP Guidance to Make Adjustments, If Needed » Checking FIPs Against Other Icing Forecast Guidance

We will use forecasts of 850-700 hPa and 925-850 hPa mean pressure layer T, RH and ‒VVEL to do the FIP check. Review the criteria in the Icing Flowchart. The FIPs will be for icing severity at FL050 (about 850 hPa) and FL090 (about 740 hPa).

Click the tabs and subtabs to view the products valid at each forecast time. Then answer the question below. Note that when comparing the mapped data, the FIPs cover a larger area than the mean pressure layer maps.

#### Question

Select the most accurate statement about the icing guidance provided by the NWP model and FIP data for 18 UTC 26 February and 00 UTC 27 February 2011.

a) FIP data do not agree sufficiently with the other NWP data to use the FIPs as guidance
b) FIP data agree well with the other NWP data at FL050 but not at FL090
c) FIP data agree well with the other NWP data at FL090 but not at FL050
d) FIP data agree well with the other NWP data at both FL090 and FL050

The correct answer is d.

Subjective review of the icing severity and SLD graphics for both flight levels reveals that their icing risk areas have similar locations and shapes to those in the mean layer guidance at both valid times. This can be seen in the graphics below, where areas conducive to icing are shaded in orange with outlines in red. The FL050 and FL090 icing severity graphics shown above are at about 850 and 740 hPa, at the top of the 925-850 hPa layer and near the top of the 850-700 hPa layer, respectively.

Please make a selection.