AIM

8/15/19

7

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1

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26

Meteorology

EXAMPLE

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

(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 observa-
tion test, one four five six zulu.”

(d)

The phrase “TEMPORARILY INOPER-

ATIVE” is added when the system is inoperative.

EXAMPLE

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“Bremerton National Airport automated weather observ-
ing 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 precipita-
tion is occurring, but the type and intensity are not
determined.

4. Ceiling and Sky Cover.

(a)

Ceiling is announced as either “CEIL-

ING” 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 observa-
tion, one four five six zulu. Ceiling two thousand overcast;”

“Bremerton National Airport automated weather observa-
tion, 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).

EXAMPLE

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“No clouds below one two thousand.”
“Clear below one two thousand.”

(c)

A sensor for determining ceiling and sky

cover is not included in some AWOS. In these
systems, ceiling and sky cover are not announced.
“SKY CONDITION MISSING” is announced only if
the system is configured with a ceilometer and the
ceiling and sky cover information is not available.

5. Remarks.

If remarks are included in the

observation, the word “REMARKS” is announced
following the altimeter setting.

(a)

Automated “Remarks.”

(1)

Density Altitude.

(2)

Variable Visibility.

(3)

Variable Wind Direction.

(b)

Manual Input Remarks. Manual input

remarks are prefaced with the phrase “OBSERVER
WEATHER.” As a general rule the manual remarks
are limited to:

(1)

Type and intensity of precipitation.

(2)

Thunderstorms and direction; and

(3)

Obstructions to vision when the visibili-

ty is 3 miles or less.

EXAMPLE

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“Remarks ... density altitude, two thousand five hundred ...
visibility variable between one and two ... wind direction
variable between two four zero and three one zero
...observed weather ... thunderstorm moderate rain
showers and fog ... thunderstorm overhead.”

(c)

If an automated parameter is “missing”

and no manual input for that parameter is available,
the parameter is announced as “MISSING.” For
example, a report with the dew point “missing” and
no manual input available, would be announced as
follows:

EXAMPLE

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“Ceiling one thousand overcast ... visibility three ...
precipitation ... temperature three zero, dew point missing
... wind calm ... altimeter three zero zero one.”

(d)

“REMARKS” are announced in the

following order of priority: