When connected to the internet, there are two icing layer options. They are "Icing (US)" and "Icing (Global)." These two options have different sources.
The Icing (US) layer comes from Forecast Icing Product (FIP) data. The FIP model is run hourly, and forecasts are available out to 18 hours.
The Icing (Global) product is based on the Global Forecast System (GFS) weather model with a coarser horizontal and vertical grid. This model is run four times per day (every 6 hours).
You can read more details about the differences in our public blog post here:
A Closer Look at Global Icing, Turbulence, and Surface Analysis Map Layers