NMD icons - these are the icons you'll see in GRLevel3 radar when viewing live L3 data and recent archived L3 data. They come from the New Mesocyclone Detection algorithm in the nexrad computer. A solid arrow-ring indicates the meso extended down to the lowest tilt. A broken ring means the meso was not found on the lowest tilt. The color "heat" of the icon represents the strength (very weak is light green, weak is green, moderate is yellow, strong is red, extreme is purple).