Icing inconsistencies with Garmin Pilot Web

On April 29, 2025, Garmin Pilot unveiled their new web-based flight planner similar to what you may find with many of the other heavyweight apps. If you are using this online planning tool, please be keenly aware that their icing forecast as of this writing is incorrect in a big way.

The first thing you will notice is that Garmin uses five categories to represent a forecast for airframe icing. This includes Trace, Light, Moderate, Severe and Extreme. From a reporting perspective, the NWS/FAA only recognizes Trace, Light, Moderate and Severe. From a forecast perspective, they recognize Trace, Light Moderate and Heavy. Heavy is used instead of severe since the term "severe" is reserved for how the aircraft reacts to the meteorological conditions (overwhelms the ice protection system), and not the meteorological conditions itself.

Next, if you look at the image above, it would appear given the dark blue color that there is a huge area of severe icing in the central Plains. Comparing this to an equivalent forecast from the Aviation Weather Center (AWC) below, notice this area is actually shown as Trace. the next contour in the Garmin Pilot forecast shows Trace which likely should be colored as Light when comparing with the AWC image below.

So what is going on here? The reason for this discrepancy, is that Garmin is misinterpreting the icing severity type that comes from the raw gridded binary files they are using (they evidently don't have a qualified meteorological consult at Garmin). That's because the way the data is coded is not optimal. It's coded in the raw source data using a single digit as shown in the table below -

So, if you look carefully at the table above, it would seem that the numerical values do not seem to be ordered in a way that makes sense...in other words, why is Trace assigned a value of (4) and not a value of (1)? Well, it's a long story, but when the NWS added the Current and Forecast Icing Potential (now they are a calibrated probability) to the gridded binary file system over 30 years ago, they discovered that the code table above for icing severity didn't have Trace or Heavy listed. It was originally None, Light, Moderate and Severe. To meet the global standards in the World Meteorological Organization (WMO) where this table is defined, they had to take the next slot available (4) and assign it to Trace and then (5) was assigned as Heavy. Changing the order of this table would have caused many other systems to become obsolete creating a great deal of havoc.

So, it appears that Garmin Pilot didn't look too carefully at this. Darn details! Furthermore, the value (3) will never show up in these raw gridded binary files for this icing forecast (although Garmin is probably assigning it to one of the five colors). And of course, (4) is evidently getting assigned as dark blue or severe from their legend.

Yes, we have reached out to their support team to notify them of this major issue. If you want the best icing forecast you can trust, check out the EZWxBrief progressive web app. Here's a depiction of the icing forecast shown in the Route Profile view that overlays actual SLD potential over the icing severity forecast.

Most pilots are weatherwise, but some are otherwise™ 

Dr. Scott Dennstaedt

Weather Systems Engineer

Founder, EZWxBrief™

CFI & former NWS meteorologist