Enroute Icing

### Produced by The COMET® Program

### Step 1: Diagnosing Locations of Icing » Satellite Data » SW IR

The shortwave IR channel lets you identify areas of day- and nighttime cloudiness along with cloud water phase during daylight. The reflected amount shows whether the cloud water is in solid or liquid form. Supercooled water clouds are brighter in daytime SW IR images, so brighter areas represent higher icing risk.

While no solar radiation is reflected at night, we can still determine if continuous, thick cirrus layers are present. If urban lights are obscured by a continuous cirrus layer, light to moderate rime icing is possible. A broken cirrus layer with visible urban lights suggests that only trace to light rime icing should be expected.

Radiosonde or model soundings provide additional information. For SW IR, if soundings show small (< 2°C) temperature-dew point spreads at cirrus level, there is a greater light-to-moderate icing threat. Typically, this is rime ice.

Here’s the SW IR animation from approximately 00 to 1302 UTC 26 Feb. Given the time of day, the sunrise terminator sweeping in from the east makes it difficult to use the imagery to diagnose potential icing in the Chicago CWSU service area. Therefore, we will not use it in this case. However, you can use it to check on the location and movement of icing areas later in the day.