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AIM

10/12/17

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)

a. TIBS, provided by FSS, is a system of

automated telephone recordings of meteorological

and aeronautical information available throughout

the United States. Based on the specific needs of each

area, TIBS provides route and/or area briefings in

addition to airspace procedures and special an-

nouncements 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 tempera-

tures 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.