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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).