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AIM

10/12/17

7

−1−28

Meteorology

3. The ASOS/AWSS data outlets include:

(a)

Those necessary for on-site airport users.

(b)

National communications networks.

(c)

Computer-generated voice (available

through FAA radio broadcast to pilots, and dial-in
telephone line).

NOTE

Wind direction broadcast over FAA radios is in reference
to magnetic north.

4.

An ASOS/AWOS/AWSS report without

human intervention will contain only that weather
data capable of being reported automatically. The
modifier for this METAR report is “AUTO.” When

an observer augments or backs

−up an ASOS/AWOS/

AWSS site, the “AUTO” modifier disappears.

5.

There are two types of automated stations,

AO1 for automated weather reporting stations
without a precipitation discriminator, and AO2 for
automated stations with a precipitation discriminator.
As appropriate, “AO1” and “AO2” must appear in
remarks. (A precipitation discriminator can deter-
mine the difference between liquid and
frozen/freezing precipitation).

NOTE

To decode an ASOS

/AWSS

 report, refer to FIG 7

−1−7 and

FIG 7

−1−8.

REFERENCE

A complete explanation of METAR terminology is located in AIM,
Paragraph 7

−1−30 , Key to Aerodrome Forecast (TAF) and Aviation

Routine Weather Report (METAR).