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AIM 

6/17/21 

aeronautical information in the cockpit helps pilots 
plan more safe and efficient flight paths, as well as 
make strategic decisions during flight to avoid 
potentially hazardous weather. 

Pilots are encouraged to provide a continuous 
exchange of information on weather, winds, 
turbulence, flight visibility, icing, etc., between pilots 
and inflight specialists. Pilots should report good 
weather as well as bad, and confirm expected 
conditions as well as unexpected. Remember that 
weather conditions can change rapidly and that a “go 
or no go” decision, as mentioned in paragraph 
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4b2, should be assessed at all phases of flight. 

g. 

Following any briefing, feel free to ask for any 

information that you or the briefer may have missed 
or are not understood. This way, the briefer is able to 
present the information in a logical sequence, and 
lessens the chance of important items being 
overlooked. 

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6.  Inflight Aviation Weather Advisories 

a.  Background 

1. 

Inflight Aviation Weather Advisories are 

forecasts to advise en route aircraft of development of 
potentially hazardous weather. Inflight aviation 
weather advisories in the conterminous U.S. are 
issued by the Aviation Weather Center (AWC) in 
Kansas City, MO, as well as 20 Center Weather 
Service Units (CWSU) associated with ARTCCs. 
AWC also issues advisories for portions of the Gulf 
of Mexico, Atlantic and Pacific Oceans, which are 
under the control of ARTCCs with Oceanic flight 
information regions (FIRs). The Weather Forecast 
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. 

b. 

SIGMET (WS)/AIRMET (WA or 

G

AIRMET) 

SIGMETs/AIRMET text (WA) products are issued 
corresponding to the Area Forecast (FA) areas 
described in FIG 

7

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4 and FIG 

7

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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 

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Meteorology