AvnWx.com Aviation Weather

Source: NOAA AWC Aviation Digital Data Service

SIGMETs

This page covers:

SIGMET

SIGMET Turbulence icon
Turbulence
SIGMET Icing icon
Icing

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:

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.

CONVECTIVE SIGMET

Source: NOAA AWC Aviation Digital Data Service

Convective SIGMET icon
Convection

Convective SIGMETs are issued for severe convective activity, which implies severe turbulence, severe icing, and low-level wind shear. Specifically:

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.

CONVECTIVE OUTLOOK

Convective SIGMET icon
Convection

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:

More information is available on the map's Forms and Controls, on the map's icons, and on the data sources.

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