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3 Answers

Metar abbreviation signification

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General Aviation

In the Metar and TAFs weather reports, we find pretty often the A02 and A01 symbols that, according to the lexical means:

Ao1: Automated Observation without precipitation discrimination

Ao2: Automated Observation with precipitation discrimination

ok, but what does this really mean ?  Sounds to me that a report with A02 won't mention if either rain or not will be present. Is that right ?


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3 Answers

  1. Best Answer

    snowpilot on May 20, 2014

    Not much help…but here is says that AO2 has the ability to determine if the precip is liquid or frozen.


    Below is a non-FAA document that describes the operation of the unit


    Go about half way down the site

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  2. Bidochon on May 21, 2014

    The second link was really useful. Thanks snowpilot.

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  3. Wes Beard on May 23, 2014

    Sometimes we don’t get enough information from standard FAA sources. Here is another government source “Office of the federal coordinator for Meteorological Services and Supporting Research” that goes into much more depth about weather stations and the associated reports.


    Page 85 of the manual has the definition of precipitation discriminator. It is a sensor, or array of sensors, that differentiates between different types of precipitation (liquid, freezing, frozen).

    It also has information about wind direction and velocity and the reported value. I didn’t know that the reported winds were a two-minute average of both direction and wind speed. If the high and low for each are greater than a certain value that information is also included. Very interesting to me. Definitely not an instanteous value like I was taught in pilot school.

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