AIM 

4/20/23 

(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

−

1

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8 and FIG 7

−

1

−

9. 

REFERENCE

−

 

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

−

1

−

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

(METAR). 

7

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1

−

32 

Meteorology