AIM 

4/20/23

 

7

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1

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32

Meteorology

(b)

National communications networks.

(c)

Computer-generated voice (available through FAA radio broadcast to pilots, and dial-in telephone

line).

NOTE

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Wind direction is reported relative to magnetic north in ATIS as well as ASOS and AWOS radio (voice) broadcasts.

4.

An ASOS/AWOS 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

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up an ASOS/AWOS 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 determine the difference between
liquid and frozen/freezing precipitation).

NOTE

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To decode an ASOS/AWOS report, refer to FIG 7

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1

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8 and FIG 7

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9.

REFERENCE

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

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28, Key to Aerodrome Forecast (TAF) and Aviation Routine Weather Report

(METAR).