METEOROLOGY FLIGHT PLANNING
When these advisories are issued, they describe potentially hazardous forecast weather conditions.
For this reason, you should always check the current WAs, WSs, and WSTs during your preflight
planning, in addition to the WW (an indirect component of the Aviation In-Flight Weather
Advisory system). CWAs and AWWs are used mainly by Air Traffic Control (ATC) agencies for
dissemination of advisories to aircraft in flight, so they are not as readily available as the other
Within the conterminous US, the National Aviation Weather Advisory Unit (NAWAU) at Kansas
City, MO, has the responsibility for issuing the five warnings. The Weather Service Forecast
Offices (WSFO) will issue them for Hawaii, Alaska, and Puerto Rico. These advisories take into
account weather conditions up to and including 45,000 feet. All heights are referenced to MSL,
except low clouds, where a ceiling layer designated by CIG is referenced to AGL. All distance
measurements are in nautical miles, and directions reference a 16-point compass. All
abbreviations are from the FAA Contractions Manual, while weather elements and obstructions to
vision are the same as those used in METARs.
Severe Weather Forecast Alert (AWW)
The AWW is a preliminary message issued in order to alert pilots that a WW is being issued. These
messages are unscheduled and are issued as required. Normally, pilots will have access to WWs
during preflight planning, and thus will not need to reference AWWs.
Convective SIGMET (WST)
WSTs are issued only for thunderstorms and related convective phenomena (as described below)
over the conterminous US. Appended to each WST is an outlook valid for up to four hours
beyond the end of the WST (Figure 3-4). They are not scheduled, but rather issued as needed,
when any of the following occurs and/or is forecast to occur for more than 30 minutes of the valid
period regardless of the size of the area affected (i.e., including isolated areas):
Lines of thunderstorms
4. Thunderstorm areas greater than or equal to thunderstorm intensity (VIP level) of four or
greater with an area of coverage of 40% or more.
5. Hail greater than or equal to 3/4 inch in diameter or greater and/or wind gusts to 50 knots or
SEVERE WEATHER WATCHES, MILITARY ADVISORIES, AND PIREPS