Updated: Sep 17, 2022
It has been over 10 years since the Graphical AIRMET or G-AIRMET has replaced the legacy AIRMET. However, it seems that on various podcasts, webinars, magazine articles and in the aviation discussion forums, pilots are still clinging to the term "AIRMET" for some reason. Perhaps it's because they don't really understand that on March 16, 2010, the G-AIRMET became the operational product for pilots and REPLACED the existing textual AIRMET. The legacy AIRMET is a byproduct of the new G-AIRMET and has stuck around for this long for a variety of reasons.
At this point in time all pilots should have long moved away from the legacy AIRMET and should now be using the G-AIRMET. In fact, the Aviation Weather Center website (https://aviationweather.gov) you will not find a graphical depiction of the legacy AIRMET. There hasn't been one for more than five years. Well, that's not entirely true. It's still there if you know the "secret" URL, but it's not part of the menu structure.
Let's do a little history lesson. The legacy AIRMET has been always a textual product that can be depicted graphically. That is, before sophisticated computer systems were in place, an aviation meteorologist issued an AIRMET solely with a keyboard typing in the forecast one character at a time. And pilots would get a briefing and pull out a map and plot the AIRMET as a polygon. When the Internet became alive with weather guidance, websites such as from aviationweather.gov started plotting these for us as polygons.
The problem with an AIRMET is that it is a forecast valid over a six hour period. Its temporal resolution long became a joke for many pilots who said that most AIRMETs were useless. It's not that they were useless, but the pilot needed to understand that the AIRMET had to cover a six hour period...what if an area of weather was moving quickly through the Midwest? Well, it had to account for that movement and the AIRMET ended up covering a lot more area. This means that some regions would likely not contain adverse weather during the six hour window, hence why pilots suggested it was useless.
Even though the legacy AIRMET still gets issued today, the primary difference is that a G-AIRMET is a "snapshot" of a particular hazard valid at a specific time (e.g., 0300Z) whereas the legacy AIRMET is valid over that six hour period. So the G-AIRMET depicts coverage of that hazard valid at a particular time within an area defined by a polygon, typically a smaller area. Consequently, the G-AIRMET provides a much better temporal resolution of the weather hazards in time and space than the legacy AIRMET.
In the case of G-AIRMETs, you will notice there's no textual component like the legacy AIRMET. Instead G-AIRMETs are strictly graphical and include some meta data. For G-AIRMETs depicting widespread moderate ice, the meta data simply consist