What are the automated station types their meaning and how to determine the automated station type from a Metar report?

Question

aviation weather documentation shows that they check for 6 automated station types.

auto_station	Indicates that the automated station type is one of the following: A01,A01A,A02,A02A,AOA,AWOS

What are the automated station types their meaning and how to determine the automated station type from a Metar report?

The following table is what I have ascertained:

auto station type	meaning	where to find in Metar report
AO1	automated station without a precipitation discriminator	there will be an AO1 after RMK
AO1A	automated station without a precipitation discriminator and manually augmented	there will be an AO1A after RMK
AO2	automated station with a precipitation discriminator	there will be an AO2 after RMK
AO2A	automated station with a precipitation discriminator and manually augmented	there will be an AO2A after RMK
AOA	?	?
AWOS	?	?
Any other automated station types?	?	?

Answer 1

If the station is fully automated then the qualifier AUTO will appear in the observation text immediately following the timestamp, e.g.

KHYS 031656Z AUTO 31011KT 10SM CLR 11/M02 A2967 RMK AO2 SLP056 T01061022 $

If the station is not fully automated then that qualifier will be missing:

KAPA 031653Z 11003KT 10SM BKN200 04/M01 A2970 RMK AO2 SLP065 T00441106

Note that both of the above examples used an automated system, as indicated by the AO2 remark. However, at Hays Regional Airport the system sent the observation into the NAS without any human observer input. At Centennial Airport a human observer checked the observation before it was disseminated and edited (or added) incomplete (or missing) elements.

If there is no automated station then there will be no AOn remark:

KMWA 031745Z 31014KT 10SM BKN006 BKN011 OVC022 10/10 A2892

This indicates that the observation was composed entirely "by hand."

In my experience I have never seen the remarks AO1A nor AO2A. The manual-augmentation status is indicated by the lack of an AUTO. I have also never seen AOA nor AWOS.

There is no explicit flag in the observation text or remarks to indicate whether the system is an AWOS or an ASOS, only whether or not it has a precipitation discriminator. However, there is one very big clue: a fully automated AWOS issues long-line observations three times per hour no matter what; a fully automated ASOS issues hourly METARs and occasional SPECIs as the conditions dictate.