Chapter 26
Advisories
26.2.3 SIGMET Standardization
SIGMETs follow these standards:
- All heights or altitudes are referenced to above MSL, unless otherwise noted, and annotated using the height in hundreds of feet, consisting of three digits (e.g., 040). For heights at or above 18,000 ft, the level is preceded by “FL” (e.g., FL180).
- References to latitude and longitude are in whole degrees and minutes following the model: Nddmm or Sddmm, Wdddmm, or Edddmm with a space between latitude and longitude and a hyphen between successive points (e.g., N3106 W07118—N3011 W7209).
- Messages are prepared in abbreviated plain language using contractions from FAA Order JO 7340.2, Contractions, for domestic products, and from ICAO Doc 8400, ICAO Abbreviations and Codes, for international products issued for Oceanic FIRs. A limited number of non-abbreviated words, geographical names, and numerical values of a self-explanatory nature may also be used.
26.2.4 Inside the CONUS
26.2.4.1 Non-Convective SIGMET
26.2.4.1.1 Non-Convective SIGMET Issuance Criteria—CONUS
A SIGMET may be issued in the CONUS when any of the following conditions affect, or, in the judgment of the forecaster, are expected to affect an area judged to have a significant impact on the safety of aircraft operations:
- Severe or greater turbulence (SEV TURB).
- Severe icing (SEV ICE).
- Widespread dust storm (WDSPR DS).
- Widespread sandstorm (WDSPR SS).
- Volcanic ash (VA).
26.2.4.1.2 Non-Convective SIGMET Issuance Time and Valid Period—CONUS
A SIGMET is an unscheduled product issued any time conditions reaching SIGMET criteria are occurring or expected to occur within a four-hour period. A SIGMET can have a valid period up to, but not exceeding, four hours. SIGMETs for continuing phenomena will be reissued at least every four hours as long as SIGMET conditions continue to occur in the area of responsibility.
26.2.4.1.3 Non-Convective SIGMET Format and Example—CONUS
The content and order of elements in the SIGMET are as follows:
- Series name and number.
- Valid beginning and ending time (UTC).
- List of states affected by the phenomena.
- Location of phenomena delineated by high-altitude VOR coordinates covering the affected area during the SIGMET valid time.
- Phenomena description (e.g., SEV ICE).
- Vertical extent (base and top), if appropriate.
- Movement, if appropriate.
- Intensity change (INTSF—intensifying, WKN—weakening, NC—no change).
- Indication that the weather condition will continue during the four hours beyond the valid time of the SIGMET.
The SIGMET in Figure 26-4 is decoded as the following:
- (Line 1) SIGMET ROMEO series issued for the San Francisco area at 0130 UTC on the 10th day of the month.
- (Line 2) This is the first issuance of the SIGMET ROMEO series and is valid until the 10th day of the month at 0530 UTC.
- (Line 3) The affected states within the San Francisco area are Oregon and Washington.
- (Line 4) From Seattle, WA; to Pendleton, OR; to Eugene, OR; to Seattle, WA.
- (Line 5) Severe turbulence between FL280 and FL350. Conditions continuing beyond 0530Z.
26.2.4.1.4 Non-Convective SIGMET Cancellations—CONUS
A CONUS Non-Convective SIGMET is cancelled when the phenomenon is no longer occurring, no longer expected to occur, or has moved out of the area of responsibility.