AIM

4/3/14

7−1−15

Meteorology

3.

Convective SIGMET bulletins are issued for

the western (W), central (C), and eastern (E) United

States. (Convective SIGMETs are not issued for

Alaska or Hawaii.) The areas are separated at 87 and

107 degrees west longitude with sufficient overlap to

cover most cases when the phenomenon crosses the

boundaries. Bulletins are issued hourly at H+55.

Special bulletins are issued at any time as required

and updated at H+55. If no criteria meeting

convective SIGMET requirements are observed or

forecasted, the message “CONVECTIVE SIGMET...

NONE” will be issued for each area at H+55.

Individual convective SIGMETs for each area (W, C,

E) are numbered sequentially from number one each

day, beginning at 00Z. A convective SIGMET for a

continuing phenomenon will be reissued every hour

at H+55 with a new number. The text of the bulletin

consists of either an observation and a forecast or just

a forecast. The forecast is valid for up to 2 hours.

EXAMPLE

−

CONVECTIVE SIGMET 44C
VALID UNTIL 1455Z
AR TX OK
FROM 40NE ADM-40ESE MLC-10W TXK-50WNW
LFK-40ENE SJT-40NE ADM
AREA TS MOV FROM 26025KT. TOPS ABV FL450.
OUTLOOK VALID 061455-061855
FROM 60WSW OKC-MLC-40N TXK-40WSW
IGB-VUZ-MGM-HRV-60S BTR-40N
IAH-60SW SJT-40ENE LBB-60WSW OKC
WST ISSUANCES EXPD. REFER TO MOST RECENT
ACUS01 KWNS FROM STORM PREDICTION CENTER
FOR SYNOPSIS AND METEOROLOGICAL DETAILS

e. International SIGMET

1.

Some NWS offices have been designated by

the ICAO as Meteorological Watch Offices (MWOs).

These offices are responsible for issuing International

SIGMETs for designated areas that include Alaska,

Hawaii, portions of the Atlantic and Pacific Oceans,

and the Gulf of Mexico.

2.

The offices which issue international

SIGMETs are:

(a)

The AWC in Kansas City, Missouri.

(b)

The AAWU in Anchorage, Alaska.

(c)

The WFO in Honolulu, Hawaii.

3.

These SIGMETs are considered “wide-

spread” because they must be either affecting or be

forecasted to affect an area of at least 3,000 square

miles at any one time. The International SIGMET is

issued for 6 hours for volcanic ash events, 6 hours for

hurricanes and tropical storms, and 4 hours for all

other events. Like the domestic SIGMETs, interna-

tional SIGMETs are also identified by an alphabetic

designator from Alpha through Mike and are

numbered sequentially until that weather phenome-

non ends. The criteria for an international SIGMET

are:

(a)

Thunderstorms occurring in lines, em-

bedded in clouds, or in large areas producing

tornadoes or large hail.

(b)

Tropical cyclones.

(c)

Severe icing.

(d)

Severe or extreme turbulence.

(e)

Dust storms and sandstorms lowering

visibilities to less than 3 miles.

(f)

Volcanic ash.

EXAMPLE

−

Example of an International SIGMET:
WSNT06 KKCI 022014
SIGA0F
KZMA KZNY TJZS SIGMET FOXTROT 3 VALID
022015/030015 KKCI

− MIAMI  OCEANIC  FIR  NEW

YORK OCEANIC FIR SAN JUAN FIR FRQ TS WI AREA
BOUNDED BY 2711N6807W 2156N6654W 2220N7040W
2602N7208W 2711N6807W. TOPS TO FL470. MOV NE
15KT. WKN. BASED ON SAT AND LTG OBS.
MOSHER

f. AIRMET

1.

AIRMETs (WAs) are advisories of signifi-

cant weather phenomena but describe conditions at

intensities lower than those which require the

issuance of SIGMETs. AIRMETs are intended for

dissemination to all pilots in the preflight and en route

phase of flight to enhance safety. AIRMET

information is available in two formats: text bulletins

(WA) and graphics (G−AIRMET). Both formats meet

the criteria of paragraph 7−1−3i1 and are issued on a

scheduled basis every 6 hours beginning at

0245 UTC. Unscheduled updates and corrections are

issued as necessary. AIRMETs contain details about

IFR, extensive mountain obscuration, turbulence,

strong surface winds, icing, and freezing levels.

2.

There are three AIRMETs: Sierra, Tango,

and Zulu. After the first issuance each day, scheduled