a prominently displayed object, as a flag or lantern, or clearly audible sound, as from a horn or siren, that signals the expected arrival of a storm:

Meteorology. a notification by the National Weather Service of anticipated or occurring winds with sustained speeds of 48 knots (55 miles per hour, 25 meters per second) to 63 knots (73 miles per hour, 32 meters per second), or frequent gusts within that range, and not directly associated with a tropical cyclone. Compare hurricane warning, warning ( def 3 ).

any sign or indication of approaching trouble, adversity, unrest, etc.: