Plain English Meaning
A UUA is a pilot's in-flight report of weather bad enough that other pilots need to hear about it right away. It gets pushed out fast because the conditions could be dangerous — things like severe icing, severe turbulence, hail, wind shear, or a tornado.
Full Definition
An urgent pilot weather report (PIREP coded UUA) is a firsthand report from a pilot in flight describing weather conditions considered hazardous enough to require immediate dissemination to other pilots and controllers. UUA reports are issued for any of the following observed conditions: tornadoes, funnel clouds, or waterspouts; (including ); severe icing; hail; ; ; and any other weather phenomenon reported that is considered by the or specialist to be hazardous to . UUA is contrasted with UA, the routine PIREP code used for non-urgent .