A SIGMET is a concise description of the occurrence or expected occurrence of specified en route weather phenomena that may affect the safety of aircraft operations. A SIGMET may be issued when an area of at least 3,000 square miles is expected to have severe or greater turbulence, severe icing, widespread duststorm, widespread sandstorm, or volcanic ash. A SIGMET is an unscheduled product issued any time conditions are occurring or expected to occur within a 4-hour period.
The most recent plot of all SIGMETs is shown below. For the full-resolution version, see the last link in the References list.