AIM

8/15/19

7

−

1

−

17

Meteorology

4. VFR.

Ceiling greater than 3,000 feet and

visibility greater than 5 miles; includes sky clear.

b.

The cause of LIFR, IFR, or MVFR is indicated

by either ceiling or visibility restrictions or both. The
contraction “CIG” and/or weather and obstruction to
vision symbols are used. If winds or gusts of 25 knots
or greater are forecast for the outlook period, the word
“WIND” is also included for all categories including
VFR.

EXAMPLE

−

1.

LIFR CIG

−

low IFR due to low ceiling.

2.

IFR FG

−

IFR due to visibility restricted by fog.

3.

MVFR CIG HZ FU

−

marginal VFR due to both ceiling

and visibility restricted by haze and smoke.

4.

IFR CIG RA WIND

−

IFR due to both low ceiling and

visibility restricted by rain; wind expected to be 25 knots or
greater.

7

−

1

−

8. Telephone Information Briefing

Service (TIBS) (Alaska Only)

a.

TIBS, provided by FSS, is a system of

automated telephone recordings of meteorological
and aeronautical information available in Alaska.
Based on the specific needs of each area, TIBS
provides route and/or area briefings in addition to
airspace procedures and special announcements
concerning aviation interests that may be available.
Depending on user demand, other items may be
provided; for example, surface weather observations,
terminal forecasts, wind and temperatures aloft
forecasts, etc.

b.

TIBS is not intended to be a substitute for

specialist

−

provided preflight briefings from FSS.

TIBS is recommended as a preliminary briefing and
often will be valuable in helping you to make a “go”
or “no go” decision.

c.

Pilots are encouraged to utilize TIBS, which can

be accessed by dialing the FSS toll

−

free telephone

number, 1

−

800

−

WX

−

BRIEF (992

−

7433) or specific

published TIBS telephone numbers in certain areas.
Consult the “FSS Telephone Numbers” section of the
Chart Supplement U.S. or the Chart Supplement
Alaska or Pacific.

NOTE

−

A touch

−

tone telephone is necessary to fully utilize TIBS.

7

−

1

−

9. Transcribed Weather Broadcast

(TWEB) (Alaska Only)

Equipment is provided in Alaska by which
meteorological and aeronautical data are recorded on
tapes and broadcast continuously over selected L/MF
and VOR facilities. Broadcasts are made from a series
of individual tape recordings, and changes, as they
occur, are transcribed onto the tapes. The information
provided varies depending on the type equipment
available. Generally, the broadcast contains a
summary of adverse conditions, surface weather
observations, pilot weather reports, and a density
altitude statement (if applicable). At the discretion of
the broadcast facility, recordings may also include a
synopsis, winds aloft forecast, en route and terminal
forecast data, and radar reports. At selected locations,
telephone access to the TWEB has been provided
(TEL

−

TWEB). Telephone numbers for this service

are found in the Chart Supplement Alaska. These
broadcasts are made available primarily for preflight
and inflight planning, and as such, should not be
considered as a substitute for specialist

−

provided

preflight briefings.

7

−

1

−

10. Inflight Weather Broadcasts

a. Weather Advisory Broadcasts.

ARTCCs

broadcast a Severe Weather Forecast Alert (AWW),
Convective SIGMET, SIGMET, or CWA alert once
on all frequencies, except emergency, when any part
of the area described is within 150 miles of the
airspace under their jurisdiction. These broadcasts
contain SIGMET or CWA (identification) and a brief
description of the weather activity and general area
affected.

EXAMPLE

−

1.

Attention all aircraft, SIGMET Delta Three, from Myton

to Tuba City to Milford, severe turbulence and severe clear
icing below one zero thousand feet. Expected to continue
beyond zero three zero zero zulu.

2.

Attention all aircraft, convective SIGMET Two Seven

Eastern. From the vicinity of Elmira to Phillipsburg.
Scattered embedded thunderstorms moving east at one
zero knots. A few intense level five cells, maximum tops four
five zero.

3.

Attention all aircraft, Kansas City Center weather

advisory one zero three. Numerous reports of moderate to
severe icing from eight to niner thousand feet in a three zero
mile radius of St. Louis. Light or negative icing reported
from four thousand to one two thousand feet remainder of
Kansas City Center area.