SIGMET,[1] or Significant Meteorological Information (AIM 7-1-6),[2] is a severe weather advisory that contains meteorological information concerning the safety of all aircraft. Compared to AIRMETs, SIGMETs cover more severe weather. Today, according to the advancement of technology in civil aviation, the SIGMET is sent as IWXXM model.[3]
faa
was invoked but never defined (see the help page).