8/15/19 3/15/07 7/16/20 AIM  7110.65R CHG 2 AIM Office (WFO) in Honolulu issues advisories for the Hawaiian Islands and a large portion of the Pacific Ocean. In Alaska, the Alaska Aviation Weather Unit (AAWU) issues inflight aviation weather advisories along with the Anchorage CWSU. All heights are referenced MSL, except in the case of ceilings (CIG) which indicate AGL. 2. There are four types of inflight aviation weather advisories: the SIGMET, the Convective SIGMET, the AIRMET (text or graphical product), and the Center Weather Advisory (CWA). All of these advisories use the same location identifiers (either VORs, airports, or well − known geographic areas) to describe the hazardous weather areas. 3. The Severe Weather Watch Bulletins (WWs), (with associated Alert Messages) (AWW) supple- ments these Inflight Aviation Weather Advisories. SIGMETs/AIRMET text (WA) products are issued corresponding to the Area Forecast (FA) areas described in FIG  7 − 1 − 4 and FIG  7 − 1 − 5. The maximum forecast period is 4 hours for SIGMETs and 6 hours for AIRMETs. The G − AIRMET is issued over the CONUS every 6 hours, valid at 3 − hour increments through 12 hours with optional forecasts possible during the first 6 hours. The first 6 hours of the G − AIRMET correspond to the 6 − hour period of the AIRMET. SIGMETs and AIRMETs are consid- ered “widespread” because they must be either affecting or be forecasted to affect an area of at least 3,000 square miles at any one time. However, if the total area to be affected during the forecast period is very large, it could be that in actuality only a small portion of this total area would be affected at any one time. 1. SIGMETs/AIRMET (or G − AIRMET) for the conterminous U.S. (CONUS) SIGMETs/AIRMET text products for the CONUS are issued corresponding to the areas in FIG 7 − 1 − 4. The maximum forecast period for a CONUS SIGMET is 4 hours and 6 hours for CONUS AIRMETs. The G − AIRMET is issued over the CONUS every 6 hours, valid at 3 − hour increments through 12 hours with optional forecasts possible during the first 6 hours. The first 6 hours of the G − AIRMET correspond to the 6 − hour period of the AIRMET. SIGMETs and AIRMETs are considered “widespread” because they must be either affecting or be forecasted to affect an area of at least 3,000 square miles at any one time. However, if the total area to be affected during the forecast period is very large, it could be that in actuality only a small portion of this total area would be affected at any one time. Only SIGMETs for the CONUS are for non-convec- tive weather. The U.S. issues a special category of SIGMETs for convective weather called Convective SIGMETs. 2. SIGMETs/AIRMETs for Alaska Alaska SIGMETs are valid for up to 4 hours, except for Volcanic Ash Cloud SIGMET s which are valid for up to 6 hours. Alaska AIRMETs are valid for up to 8 hours. 3. SIGMETs/AIRMETs for Hawaii and U.S. FIRs in the Gulf of Mexico, Caribbean, Western Atlantic and Eastern and Central Pacific Oceans These SIGMETs are valid for up to 4 hours, except SIGMETs for Tropical Cyclones and Volcanic Ash Clouds, which are valid for up to 6 hours. AIRMETs are issued for the Hawaiian Islands and are valid for up to 6 hours. No AIRMETs are issued for U.S. FIRs in the the Gulf of Mexico, Caribbean, Western Atlantic and Pacific Oceans. A SIGMET advises of weather that is potentially hazardous to all aircraft. SIGMETs are unscheduled products that are valid for 4 hours. However, SIGMETs associated with tropical cyclones and volcanic ash clouds are valid for 6 hours. Unscheduled updates and corrections are issued as necessary. 1. In the CONUS, SIGMETs are issued when the following phenomena occur or are expected to occur: (a) Severe icing not associated with thunder- storms. (b) Severe or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms. (c) Widespread dust storms or sandstorms lowering surface visibilities to below 3 miles. (d) Volcanic ash. 2. In Alaska and Hawaii, SIGMETs are also issued for: (a) Tornadoes. c. SIGMET b. SIGMET (WS)/AIRMET (WA or G − AIRMET) Meteorology 7 − 1 − 10