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AIM

10/12/17

7−1−32

Meteorology

TBL 7−1−4

SERVICE LEVEL A
Service Level A consists of all the elements of

Service Levels B, C and D plus the elements

listed to the right, if observed.

10 minute longline RVR at precedented sites or

additional visibility increments of 1/8, 1/16 and 0

Sector visibility

Variable sky condition

Cloud layers above 12,000 feet and cloud types

Widespread dust, sand and other obscurations

Volcanic eruptions

SERVICE LEVEL B
Service Level B consists of all the elements of

Service Levels C and D plus the elements listed to

the right, if observed.

Longline RVR at precedented sites

(may be instantaneous readout)

Freezing drizzle versus freezing rain

Ice pellets

Snow depth & snow increasing rapidly remarks

Thunderstorm and lightning location remarks

Observed significant weather not at the station

remarks

SERVICE LEVEL C
Service Level C consists of all the elements of Service

Level D plus augmentation and backup by a human

observer or an air traffic control specialist on location

nearby. Backup consists of inserting the correct value if

the system malfunctions or is unrepresentative.

Augmentation consists of adding the elements listed to

the right, if observed. During hours that the observing

facility is closed, the site reverts to Service Level D.

Thunderstorms

Tornadoes

Hail

Virga

Volcanic ash

Tower visibility

Operationally significant remarks as deemed

appropriate by the observer

SERVICE LEVEL D
This level of service consists of an ASOS or AWSS

continually measuring the atmosphere at a point near the

runway. The ASOS or AWSS senses and measures the

weather parameters listed to the right.

Wind

Visibility

Precipitation/Obstruction to vision

Cloud height

Sky cover

Temperature

Dew point

Altimeter

7−1−13. Weather Radar Services

a. The National Weather Service operates a

network of radar sites for detecting coverage,

intensity, and movement of precipitation. The

network is supplemented by FAA and DOD radar

sites in the western sections of the country. Local

warning radar sites augment the network by operating

on an as needed basis to support warning and forecast

programs.

b. Scheduled radar observations are taken hourly

and transmitted in alpha-numeric format on weather

telecommunications circuits for flight planning

purposes. Under certain conditions, special radar

reports are issued in addition to the hourly

transmittals. Data contained in the reports are also

collected by the National Center for Environmental

Prediction and used to prepare national radar

summary charts for dissemination on facsimile

circuits.

c. A clear radar display (no echoes) does not mean

that there is no significant weather within the

coverage of the radar site. Clouds and fog are not

detected by the radar. However, when echoes are

present, turbulence can be implied by the intensity of

the precipitation, and icing is implied by the presence

of the precipitation at temperatures at or below zero

degrees Celsius. Used in conjunction with other

weather products, radar provides invaluable informa-

tion for weather avoidance and flight planning.