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AIM CHG 2
(b) National communications networks.
(c) Computer-generated voice (available
through FAA radio broadcast to pilots, and dial-in
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
To decode an ASOS/AWSS report, refer to FIG 7-1-5 and
A complete explanation of METAR terminology is located in AIM,
Paragraph 7-1-29 , Key to Aerodrome Forecast (TAF) and Aviation
Routine Weather Report (METAR).