Aeronautical Information Manual (AIM)

AIM

4/3/14

7−1−17

Meteorology

(e)

Turbulence

(f)

Low level wind shear (LLWS)

(g)

Strong surface winds

G−AIRMETs are snap shots at discrete time intervals

as defined above. The text AIRMET is the result of

the production of the G−AIRMET but provided in a

time smear for a 6hr valid period. G−AIRMETs

provide a higher forecast resolution than text

AIRMET products. Since G−AIRMETs and text

AIRMETs are created from the same forecast

“production” process, there exists perfect consist-

ency between the two. Using the two together will

provide clarity of the area impacted by the weather

hazard and improve situational awareness and

decision making.

Interpolation of time periods between G−AIRMET

valid times: Users must keep in mind when using the

G−AIRMET that if a 00 hour forecast shows no

significant weather and a 03 hour forecast shows

hazardous weather, they must assume a change is

occurring during the period between the two

forecasts. It should be taken into consideration that

the hazardous weather starts immediately after the 00

hour forecast unless there is a defined initiation or

ending time for the hazardous weather. The same

would apply after the 03 hour forecast. The user

should assume the hazardous weather condition

is occurring between the snap shots unless informed

otherwise. For example, if a 00 hour forecast shows

no hazard, a 03 hour forecast shows the presence of

hazardous weather, and a 06 hour forecast shows no

hazard, the user should assume the hazard exists from

the 0001 hour to the 0559 hour time period.

EXAMPLE

−

See FIG 7

−1−8 for an example of the G−AIRMET

graphical product.

g. Severe Weather Watch Bulletins (WWs) and

Alert Messages (AWWs)

WWs define areas of possible severe

thunderstorms or tornado activity. The bulletins are

issued by the Storm Prediction Center (SPC) in

Norman, OK. WWs are unscheduled and are issued

as required.

A severe thunderstorm watch describes areas

of expected severe thunderstorms. (Severe thunder-

storm criteria are

−inch hail or larger and/or wind

gusts of 50 knots [58 mph] or greater.)

A tornado watch describes areas where the

threat of tornadoes exists.

In order to alert the WFOs, CWSUs, FSSs,

and other users, a preliminary notification of a watch

called the Alert Severe Weather Watch bulletin

(AWW) is sent before the WW. (WFOs know this

product as a SAW).

EXAMPLE

−

Example of an AWW:
MKC AWW 011734
WW 75 TORNADO TX OK AR 011800Z

−020000Z

AXIS..80 STATUTE MILES EAST AND WEST OF A
LINE..60ESE DAL/DALLAS TX/

− 30 NW ARG/ WALNUT

RIDGE AR/

..AVIATION COORDS.. 70NM E/W /58W GGG

− 25NW

ARG/
HAIL SURFACE AND ALOFT..1

INCHES. WIND

GUSTS..70 KNOTS. MAX TOPS TO 450. MEAN WIND
VECTOR 24045.

Soon after the AWW goes out, the actual

watch bulletin itself is issued. A WW is in the

following format:

(a)

Type of severe weather watch, watch area,

valid time period, type of severe weather possible,

watch axis, meaning of a watch, and a statement that

persons should be on the lookout for severe weather.

(b)

Other watch information; i.e., references

to previous watches.

(c)

Phenomena, intensities, hail size, wind

speed (knots), maximum cumulonimbus (CB) tops,

and estimated cell movement (mean wind vector).

(d)

Cause of severe weather.

(e)

Information on updating Convective

Outlook (AC) products.

EXAMPLE

−

Example of a WW:
BULLETIN

− IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 381
STORM PREDICTION CENTER NORMAN OK
556 PM CDT MON JUN 2 1997
THE STORM PREDICTON CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF NORTHEAST
NEW MEXICO TEXAS PANHANDLE
EFFECTIVE THIS MONDAY NIGHT AND TUESDAY
MORNING FROM 630 PM UNTIL MIDNIGHT CDT.
TORNADOES...HAIL TO 2

INCHES IN DIAME-

TER...THUNDERSTORM WIND GUSTS TO 80
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE
IN THESE AREAS.