Enroute Icing

### Produced by The COMET® Program

### Step 3: Use NWP Guidance to Make Adjustments, If Needed » FIP Data for Icing Forecast

Below are the three types of FIP data (probability of icing, icing severity where probabilities are greater than 50%, and icing severity with location of SLD) from 15 UTC 26 Feb to 00 UTC 27 Feb for flight levels 050, 070, 090, and 110.

Compare the FIPs to the first forecast, looking for any changes that should be made to the first forecast icing area coverage, icing intensity, and icing levels for the CWSU service area during the forecast period. Then you will make any changes that are needed to the first forecast in the question at the bottom of the page.

#### Probability of Icing

#### Severity of Icing (Probability > 50%)

#### Severity of Icing, Risk of SLD

#### Question

Select any changes that should be made to the first forecast icing area coverage, icing intensity, and icing levels for the Chicago CWSU service area during the forecast period.

a) Adjust Illinois section of 15 UTC boundary northward to Wisconsin border
b) Remove the icing threat after 19 UTC for the service area
c) Have the icing threat completely cover the service area by 19 UTC
d) Increase lowest flight level for the icing threat to FL090 at 19 UTC
e) Increase highest flight level for the icing threat to FL120 through the forecast
f) Increase icing intensity to moderate to occasionally severe from FL100 through 120
g) Remove icing threat at all FLs over eastern Iowa and western Illinois by 19 UTC

The correct answers are a, c, e.

The icing severity chart for 15 UTC at FL070 shows moderate intensity icing north of the first forecast icing area (inside the circle).

Reviewing the 18 UTC forecasts for all FLs, we see that icing has spread into much of southern Wisconsin and southwestern lower Michigan. Moderate icing is found as high as FL110 in the northern and northeastern portions of our service area. Moderate or greater icing with areas of SLD is forecast from FL050 through FL090 in the western portions of the service area.

By 21 UTC, the entire service area is covered with at least light icing. The central portion has at least moderate icing and areas of SLD, which implies the potential for even severe clear or mixed icing. At FL110, the moderate icing is found at 18 UTC, while somewhat further north and east, it still can be found in the Wisconsin, Michigan, and Indiana portions of the service area. Meanwhile, icing conditions from FL050 through 090 in the western part of the service area remain significant, especially at FLs 050 and 070.

After taking the forecast into account and making the adjustments, your final forecast should look something like this.

A possible Met Information Statement (MIS) from 15 UTC through 19 UTC 26 February might read:

OB MIS 02 VALID 261500-262100 ...FOR ATC PLANNING PURPOSES ONLY... E Iowa/all of Illinois/NW Indiana/SW Lower Mich/SE Wisc/lower third Lk Mich.. Modt ocnl svr icing in clds and prcp blw FL100. Rest of ZAU, light to moderate icing in clds and prcp blw FL120. Modt ocnl severe icing in clds/prcp blw FL120 entire ZAU by 18Z cont beyond 21Z at and blw FL090, but impr frm sw above FL090 after 21Z.

Please make a selection.