Severe Weather Forecast Alert (AWW)

CHAPTER THREE

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

three advisories.

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):

Tornadoes

Lines of thunderstorms

Embedded 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

greater.

3-10

SEVERE WEATHER WATCHES, MILITARY ADVISORIES, AND PIREPS