SIGMETs, AIRMETs, PIREPs - What You Need to Know Before You Go (Credit: Meteorologist Jessica Olsen & AWC)
DISCUSSION: Hazardous in-flight weather advisory service (HIWAS) is a program for broadcasting hazardous weather information on a continuous basis over selected VORs (VHF omnidirectional range, it effectively allows the receiver the measure its bearing to or from the beacon, when used in conjunction with a DME (distance measuring equipment) the measurements allow for a position fix, posing a two-fold benefit to using VORs. While HIWAS can be transmitted through the VOR, advisories that are sent to pilots include AIRMETS, SIGMETS, convective SIGMETs, and PIREPs (read below).
According to the Aviation Weather Center, AIRMETs, (AIRman's METeorological Information), "advises of weather that may be hazardous, other than convective activity, to single engine, other light aircraft, and Visual Flight Rule (VFR) pilots." These are often considered widespread, affecting an area of at least 3000 square miles, and are typically issued every 6 hours, which can be amended when needed due to condition/issuance change.
While a SIGMET (SIGnificant METeorological Information), according to the Aeronautical Information Manual (FAR AIM) is used to, "advise of non-convective weather that is potentially hazardous to all aircraft." These are often unscheduled but valid for a period of 4 hours, unless associated with a hurricane then valid for 6 hours, similarly to the AIRMET, it can be amended when needed. SIGMETs can be issued for reasons such as volcanic ash, severe icing not associated with thunderstorms, widespread dust storms or sandstorms lowering surface visibilities to below 3 miles, and a variety of other phenomena listed in the FAR AIM. Convective SIGMETs can also be issued and are associated with severe thunderstorms, embedded thunderstorms, squall line thunderstorms, and thunderstorms producing precipitation greater than or equal to heavy precipitation affecting 40 percent or more of an area at least 3000 square miles.
Lastly PIREPs (PIlot Weather REPorts), as stated by the Aviation Weather Center, "is reported by a pilot to indicate encounters of hazardous weather such as icing or turbulence." PIREPs are not limited to icing and turbulence but could include reports for ceilings at or below 5000 feet, wind shear, volcanic ash, and several other conditions found in the FAR AIM.
Aviators are given a variety of tools to interpret weather, in conjunction with present and future flights. While much of the reporting that pilots use are often available within the ATIS (Automatic Terminal Information Service), a tool that disseminates valuable information regarding current conditions, approach/departure, instructions and more, it is all being verified after the pilot reports the ICAO letter associated with the ATIS report indicating the pilot has reviewed current ATIS information to the controller (tower, ground, approach/departure, center), some ATIS reports will communicate SIGMETs/AIRMETs/PIREPs in addition to the standard, abbreviates or outlook brief that a pilot could obtain from 1800WXBrief.
For more information on aviation meteorology visit the Global Weather and Climate Center!
© Meteorologist Jessica Olsen
F. (2014, April 3). Retrieved May 27, 2019, from http://www.faraim.org/aim/aim-4-03-14-437.html
N. (n.d.). What is an AIRMET? Retrieved from https://www.weather.gov/source/zhu/ZHU_Training_Page/Weather_Keys/AIRMETs/AIRMET.htm
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