CONVECTIVE OUTLOOKs: Forecasts of potential Convective Weather
SIGMETs are Inflight Weather Advisories for Significant Meteorological hazards. A SIGMET is "widespread" in
that it covers an area of at least 3,000 square miles. Note that the particular hazard may be present in only a
small portion of the area at any particular time.
A SIGMET may be issued at any time, and has a maximum forecast period of 4 hours (6 hours for hurricanes).
Each forecast area will issue a separate SIGMET if any part
of the weather hazard is within the forecast area. These forecast areas in the continental US) correspond to the
FA Area Forecast locations: SFO/San Francisco, SLC/Salt Lake City, CHI/Chicago,
DFW/Dallas-Fort Worth, BOS/Boston, and MIA/Miami. Alaska, Hawaii issue their own SIGMETs.
SIGMETs are issued for:
Severe Icing (not associated with thunderstorms -- otherwise, it is a Convective SIGMET)
Severe Turbulence (similarly, only if not associated with thunderstorms)
Duststorms and sandstorms lowering visibility to less than three miles
In Alaska and Hawaii, SIGMETs are also issued for tornadoes, a line of thunderstorms, embedded thunderstorms, or hail
greater than or equal to 3/4 inch.
Because the issued area is very large, PIREPs are useful to see current conditions in the area.
Source: NOAA AWC Aviation Digital Data Service
Convective SIGMETs are issued for severe convective activity, which implies severe turbulence, severe icing, and
low-level wind shear. Specifically:
A line of thunderstorms
Thunderstorms with heavy precipitation affecting 40%+ of an area at least 3,000 square miles
Surface winds 50+ knots due to severe thunderstorm
Hail 3/4+ inches in diameter
A Convective SIGMET is issued every hour (at H+55) for each of three
continental US regions (Alaska and Hawaii only issue
SIGMETs.) If no convective SIGMET is forecast then the region issues "CONVECTIVE SIGMET...NONE". AvnWx.com does not
display "None" Convective SIGMETs.
Because they are issued every hour, AvnWx.com may show more than one Convective SIGMET
at the same time. Also, given some overlap in reporting regions, you may notice a two advisories issued by
two regions (say, West and Central) repeating most of the same information. Check carefully, because often there are
slight differences between the advisories.
If the CONVECTIVE SIGMET contains only forecast information, it is called an Outlook. Convective Outlooks
provide some information in the text, but refer to reader to the most recent ACUS01 KWNS from
the Storm Prediction Center. ("ACUS01" is the one-day (01) anticipated convection (AC) report; "KWNS" is the
station id for Norman, Oklahoma Storm Prediction Center. This report is available as the
One Day Outlook at NOAA.
Outlook forecast are valid for up to 2 hours.
SIGMETs and AIRMETs are available from Enroute Flight Advisory Service (EFAS, better known
as Flight Watch) on 122.0MHz
(high altitude frequencies differ). In addition to Flight Watch, weather advisories are provided with
standard Pre-Flight Briefing from AFSS or 1-800-WX-BRIEF.
Information on this page is derived from AC 00-45E, and the AIM.
For further information, see: