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AIM

10/12/17

7−1−31

Meteorology

e. TBL 7−1−3 contains a comparison of weather

observing programs and the elements reported.

f. Service Standards. During 1995, a govern-

ment/industry team worked to comprehensively

reassess the requirements for surface observations at

the nation’s airports. That work resulted in agreement

on a set of service standards, and the FAA and NWS

ASOS sites to which the standards would apply. The

term “Service Standards” refers to the level of detail

in weather observation. The service standards consist

of four different levels of service (A, B, C, and D) as

described  below. Specific observational elements

included in each service level are listed in

TBL 7−1−4.

1. Service Level D defines the minimum

acceptable level of service. It is a completely

automated service in which the ASOS/AWSS

observation will constitute the entire observation,

i.e., no additional weather information is added by a

human observer. This service is referred to as a stand

alone D site.

2. Service Level C is a service in which the

human observer, usually an air traffic controller,

augments or adds information to the automated

observation. Service Level C also includes backup of

ASOS/AWSS elements in the event of an ASOS/

AWSS malfunction or an unrepresentative

ASOS/AWSS report. In backup, the human observer

inserts the correct or missing value for the automated

ASOS/AWSS elements. This service is provided by

air traffic controllers under the Limited Aviation

Weather Reporting Station (LAWRS) process, FSS

and NWS observers, and, at selected sites,

Non−Federal Observation Program observers.

Two categories of airports require detail beyond

Service Level C in order to enhance air traffic control

efficiency and increase system capacity. Services at

these airports are typically provided by contract

weather observers, NWS observers, and, at some

locations, FSS observers.

3. Service Level B is a service in which weather

observations consist of all elements provided under

Service Level C, plus augmentation of additional data

beyond the capability of the ASOS/AWSS. This

category of airports includes smaller hubs or special

airports in other ways that have worse than average

bad weather operations for thunderstorms and/or

freezing/frozen precipitation, and/or that are remote

airports.

4. Service Level A, the highest and most

demanding category, includes all the data reported in

Service Standard B, plus additional requirements as

specified. Service Level A covers major aviation

hubs and/or high volume traffic airports with average

or worse weather.

TBL 7−1−3

Weather Observing Programs

Element

Reported

W

ind

V

isibility

Temperatur

e

Dew Point

Altimeter

Density 

Altimeter

Cloud/Ceiling

Pr

ecipitation

Identification

Thunderstorm

/

Lightning

Pr

ecipitation

Occurr

ence

Rainfall

Accumulation

Runway Surface

Condition

Fr

eezing Rain

Occurr

ence

Remarks

Type

AWSS

X

X

X

X

X

X

X

X

X

X

ASOS

X

X

X

X

X

X

X

X

X

X

AWOS−A

X

AWOS−A/V

X

X

AWOS−1

X

X

X

X

AWOS−2

X

X

X

X

X

AWOS−3

X

X

X

X

X

X

AWOS−3P

X

X

X

X

X

X

X

AWOS−3T

X

X

X

X

X

X

X

AWOS−3P/T

X

X

X

X

X

X

X

X

AWOS−4

X

X

X

X

X

X

X

X

X

X

X

X

Manual

X

X

X

X

X

X

X

REFERENCE− FAA Order JO 7900.5B, Surface Weather Observing, for element reporting.