AIM

4/20/23

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Meteorology

Instrument Approach Procedures. Selected individual systems may be incorporated into nationwide data
collection and dissemination networks in the future.

c. AWOS Broadcasts.

Computer-generated voice is used in AWOS to automate the broadcast of the

minute-by-minute weather observations. In addition, some systems are configured to permit the addition of an
operator-generated voice message; e.g., weather remarks following the automated parameters. The phraseology
used generally follows that used for other weather broadcasts. Following are explanations and examples of the
exceptions.

1. Location and Time.

The location/name and the phrase “AUTOMATED WEATHER OBSERVA-

TION,” followed by the time are announced.

(a)

If the airport’s specific location is included in the airport’s name, the airport’s name is announced.

EXAMPLE

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“Bremerton National Airport automated weather observation, one four five six zulu;”
“Ravenswood Jackson County Airport automated weather observation, one four five six zulu.”

(b)

If the airport’s specific location is not included in the airport’s name, the location is announced

followed by the airport’s name.

EXAMPLE

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“Sault Ste. Marie, Chippewa County International Airport automated weather observation;”
“Sandusky, Cowley Field automated weather observation.”

(c)

The word “TEST” is added following “OBSERVATION” when the system is not in commissioned

status.

EXAMPLE

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“Bremerton National Airport automated weather observation test, one four five six zulu.”

(d)

The phrase “TEMPORARILY INOPERATIVE” is added when the system is inoperative.

EXAMPLE

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“Bremerton National Airport automated weather observing system temporarily inoperative.”

2. Visibility.

(a)

The lowest reportable visibility value in AWOS is “less than 

1

/

4

.” It is announced as “VISIBILITY

LESS THAN ONE QUARTER.”

(b)

A sensor for determining visibility is not included in some AWOS. In these systems, visibility is not

announced. “VISIBILITY MISSING” is announced only if the system is configured with a visibility sensor and
visibility information is not available.

3. Weather.

In the future, some AWOSs are to be configured to determine the occurrence of precipitation.

However, the type and intensity may not always be determined. In these systems, the word “PRECIPITATION”
will be announced if precipitation is occurring, but the type and intensity are not determined.

4. Ceiling and Sky Cover.

(a)

Ceiling is announced as either “CEILING” or “INDEFINITE CEILING.” With the exception of

indefinite ceilings, all automated ceiling heights are measured.

EXAMPLE

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“Bremerton National Airport automated weather observation, one four five six zulu. Ceiling two thousand overcast;”

“Bremerton National Airport automated weather observation, one four five six zulu. Indefinite ceiling two hundred, sky
obscured.”

(b)

The word “Clear” is not used in AWOS due to limitations in the height ranges of the sensors. No

clouds detected is announced as “NO CLOUDS BELOW XXX” or, in newer systems as “CLEAR BELOW
XXX” (where XXX is the range limit of the sensor).