This chapter describes the types of aviation surface weather observing facilities for which the FAA may have responsibility or oversight. This chapter also describes the various types of surface weather reports, including the Aviation Routine Weather Report (METAR) and Aviation Selected Special Weather Report (SPECI), and FAA guidelines regarding the content of each of these types. Also presented are general guidelines regarding augmentation and backup of automated observations. Lastly, this chapter presents FAA guidelines on the certification of observers.

2-2.   TYPES OF STATIONS

The generic types of stations that take aviation weather observations are defined as follows:

a.  Automated Station. A facility equipped with an automated surface weather observing system that prepares the observation without a certified observer on duty. The various types of automated stations are described in Chapter 4, General Procedures at Automated Weather Stations.

b.  Augmented Station. A facility with an automated surface weather observing system that prepares the METAR/SPECI with a certified observer on duty capable of adding operationally significant weather information to the observation. The observer is completely responsible for the observation, even though the automated weather observing system generates the report. At facilities where augmentation is not available full time, the facility is classed as automated during the non-augmented periods.

c.  Manual Station. A facility where certified weather observers are responsible for observing, evaluating and preparing the METAR/SPECI. At these facilities, various degrees of automated sensors and/or other automated equipment may be available. However, the observer is completely responsible for the METAR/SPECI.

d.  Towered Station. Any facility with an air traffic control tower operated by the FAA or operated under an FAA contract.

e.  Non-Towered Station. Any facility without an FAA or FAA contract air traffic control tower.

f.  Limited Aviation Weather Reporting Station (LAWRS). A facility where observations are taken, prepared and transmitted by certified FAA or FAA-contract control tower personnel or Flight Service Station personnel on a limited basis to support aviation requirements. At these facilities, various degrees of automated sensors and/or other automated equipment may be available. However, when the facility is open, the LAWRS observer is completely responsible for the METAR/SPECI. At an automated site ranked as Service Level C, the basic weather observing requirements are the same as a LAWRS observation.

g.  Flight Service Station. Throughout this order, the term Flight Service Station (FSS) refers to any Flight Service Station, Automated Flight Service Station (AFSS), Auxiliary Flight Service Station, or former FSS airport facility which has been directed by FAA national or regional headquarters to provide the observing, augmentation or backup service indicated.

h.  Supplementary Aviation Weather Reporting Station (SAWRS). This program is maintained by the NWS. To obtain more information, contact the nearest NWS Weather Forecast office.

i.  Non-Federal Observing (NF-OBS) Station. A program in which Non-Federal observers such as Non-Federal control tower (NFCT) controllers, airline personnel or fixed base operator (FBO) personnel may enter into an agreement with the appropriate FAA region to provide backup and augmentation of the Automated Surface Observing System (ASOS). NF-OBS observers are certified by NWS. At these facilities, various degrees of automated sensors and/or other automated equipment may be available. However, when on duty, the NF-OBS observer shall provide backup and augmentation in accordance with their NF-OBS agreement. Program establishment is contained in Appendix B, Non-Federal Observing (NF-OBS) Program, and responsibilities are described in Chapter 4, General Procedures at Automated Weather Stations.

j.  A-Paid Station. A facility where contract observers take only hourly observations (METAR). SPECI observations are not taken at these facilities.

There are two general types of surface observations:

a.  Automated Observation. Any observation which has been evaluated, prepared and transmitted by an automated observing system without human intervention. The automated observing systems to which this order applies include only Automated Surface Observing Systems (ASOS) and the Automated Weather Observing Systems (AWOS).

(1)  Augmentation.  Any automated observation to which additional weather information has been manually added that is beyond the capabilities of the automated weather observing system and/or is deemed operationally significant. The guidelines concerning augmentation are presented in paragraph 2-4.

(2)  Backup.  A method of providing an observation, part of an observation, documentation, or communication of an observation at selected sites when the primary method is unavailable or non-representative. The guidelines concerning manually provided backup information are presented in paragraph 2-5, Backup Requirements.

b.  Manual Observation. Any observation for which the human observer observes, evaluates, prepares, records, and transmits the observation without the use of an automated observing system. The guidelines for manual observations are presented in Chapter 7, General Procedures for Manual Observations.

Certified observers are responsible for the completeness and accuracy of the weather observation. Automated weather observing systems are, by design, viewing a smaller area than a human observer. Therefore, the observer is responsible for providing additional information that covers a larger area, when operationally significant. Augmentation of automated observations shall be provided in accordance with the guidelines presented in the following subsections and as specified for the station’s service level standard (Appendix D, Service Standards). Separate guidelines are presented for the two general types of automated weather observing systems: ASOS and AWOS. Procedures and practices to be followed to accomplish the required augmentation are presented in Chapter 4, General Procedures at Automated Weather Stations, and Chapter 5, Augmentation at Automated Weather Stations.

a.  Control Tower with ASOS.

(1)  Control Tower without a Surface-Based Observer. At facilities with a control tower and with ASOS, but without a surface-based observer on duty, the tower observer shall provide augmentation of the automated observation. This augmentation shall include, but not be limited to:

(a)  thunderstorm

(b)  tornadic activity (including tornado, waterspout and funnel cloud)

(c)  hail

(d)  virga

(e)  volcanic ash

(f)  any weather elements considered operationally significant by the observer

(2)  Control Tower with a Surface-Based Observer. At facilities with a control tower, with ASOS and with a surface-based observer on duty, the surface-based observer shall provide augmentation of the automated observation. This augmentation shall include, but not be limited to the requirements contained in Service Standards for that level of airport (see Appendix D, Service Standards). At these facilities, the control tower shall routinely provide tower visibility when applicable.

b.  Facilities without Control Towers with ASOS. At these facilities, augmentation shall be the responsibility of the co-located Flight Service Station or contract weather observer (CWO) at designated stations. This augmentation shall include, but not be limited to:

(1)  thunderstorm

(2)  tornadic activity (including tornado, waterspout, and funnel cloud)

(3)  hail

(4)  virga

(5)  volcanic ash

(6)  any weather elements considered operationally significant by the observer

c.  Facilities with AWOS. At these facilities, the observation shall be the responsibility of the surface-based observer if one exists. At towered sites without a surface-based observer, the observation shall be the responsibility of the LAWRS observer. (Note: Augmentation is not possible at AWOS facilities without an operator interface device.) (Appendix E, METAR User Aids, contains a quick reference for METAR codes.) The augmentation provided by the observer shall be manually entered into the system for transmission via the operator terminal keyboard. If a "hot key" is not available for a particular augmentable element, the augmentation entries shall be manually entered into the remarks portion of the observation and shall be limited to 80 characters including spaces. The following elements shall be provided:

(1)  Thunderstorms.

(2)  Precipitation occurring at the point of observation, limited to type plus intensity. Allowable reports are listed in Figure 6-6, Backup and Augmentation Weather and Obscurations, and in Appendix E, METAR User Aids.

(3)  Obscurations (alone or in combination with precipitation) at the point of observation. Allowable reports are listed in Figure 6-6 and in appendix E.

(4)  Operationally significant, localized weather conditions, not listed above, as follows:

(a)  hail

(b)  virga

(c)  tornadic activity* (includes tornado, waterspout, or funnel cloud)

(d)  volcanic ash*

(e)  any weather elements considered operationally significant by the observer

Note:  Only those episodes of weather phenomena listed above that are occurring within a five mile radius of the airport, and/or that pose an operational hazard for aircraft in the airport area shall be reported. Weather phenomena marked with an asterisk (*) shall be reported immediately using the AWOS manual observation mode for entry and transmission. Because AWOS can only produce observations for long-line transmission every 20 minutes, these observations will go out as a METAR, but will be available for local operations via the one-minute data mode.

a.  Situations Requiring Backup. Certified observers are responsible for the completeness and accuracy of the weather observation. If the complete automated observation is unavailable due to sensor/system malfunction, communications failure, and/or non-representative data, backup information shall be provided in accordance with the guidelines in the following subsections. Backup refers to the observer providing the same reporting capability as that provided by the automated weather sensor, consistent with service level standards specified in Appendix D, Service Standards. Backup information is required for long-line dissemination for terminal forecast (TAF) production and for local, ground-to-air dissemination to legally sustain local operations at the airport. The "failure" modes mentioned above are defined as follows:

(1)  Sensor/system Malfunction. One or more sensors or the entire observing system is(are) not reporting data (for any reason). Provide manual backup and make appropriate maintenance notifications.

(2)  Communications Failure. The automated weather observing system and/or long-line communications are malfunctioning, thereby preventing the entry and/or transmission of the observation over long-line networks. When it is apparent that observations are not being transmitted, relay the observations to the tie-in FSS and notify the appropriate office for outage notification.

(3)  Non-representative Data. The sensor is reporting data, but the data are incorrect, or the sky condition, visibility and/or present weather sensor(s) is/are accurately reporting conditions in the vicinity of the sensor, but those conditions are not representative of prevailing conditions for the operating areas of the airport and are considered operationally significant. When this occurs, provide manual backup. Outage notification is not required.

b.  Level of Support. The information specified in these guidelines is the minimum required for each of the situations discussed in the following subsections. The FAA may specify additional information beyond this minimum. The observer is encouraged to add any other appropriate remarks. Procedures and practices to provide the required backup information are presented in Chapter 6, Backup Requirements at Automated Weather Stations.

c.  Communications. Automated weather observing system failure may or may not include loss of long-line communications, local communications, or both. The level of backup information to be provided depends on the status of such communications and whether the information is required for long-line or local, ground-to-air dissemination.

d.  Equipment for Backup Observations. Weather observing equipment should be maintained to allow certified observers to perform backup responsibilities in the event of an automated sensor failure. Air Traffic managers shall coordinate with the regional Air Traffic Division, local AF Maintenance, and the appropriate NWS regional office prior to initiating action to decommission weather observing equipment.

Details on the procedures to provide backup are in Chapter 6, Backup Requirements at Automated Weather Stations. This paragraph specifies the type of minimum backup for various types of facilities.

a. LAWRS Towers. At LAWRS towers, certified air traffic control specialists (ATCS) shall provide the backup information for long-line transmission which is listed in this section. The required information shall be entered into the automated weather observing system via the operator interface device. The following information shall be provided at a minimum:

(1)  Wind

(2)  Visibility to 10 miles

(3)  Present weather and obstructions to vision (see Figure 6-6 for required elements)

(4)  Sky condition to 12,000 feet

(5)  Temperature/Dew Point

(6)  Altimeter setting

(7)  Required remarks and operationally significant remarks as deemed appropriate (Note: Precipitation of unknown form may be reported only if the automated sensor is operational and is reporting precipitation of unknown form. However, if the observer can determine the type of precipitation, it should be reported using the allowable elements listed in Figure 6-6, Backup and Augmentation Weather and Obscurations.)

b.  Non-LAWRS Towers with a Surface-Based Observer. At non-LAWRS towers with a surface-based observer, the surface-based observer shall provide at a minimum the backup information for long-line transmission according to the requirements contained in the Service Standards for the service level of the airport. Backup shall also include required remarks and operationally significant remarks as deemed appropriate by the observer. At these facilities, tower personnel shall routinely provide tower visibility information to the surface-based observer as required.

c.  Non-Towered Facilities with a Surface-Based Observer. At all non-towered facilities, the surface-based observer shall provide the backup information required by the Service Standards for the service level of the airport. At all facilities with an operator interface device, the required information shall be entered into the automated weather observing system via the operator interface device. Backup shall also include required remarks and operationally significant remarks as deemed appropriate by the observer.

Prior to assuming full responsibility for taking any type of surface observation or any part thereof, each person shall be certified. The NWS is responsible for certifying all civilian weather observers in one or more of the following observer types:

a.  NWS and FAA observers

b.  LAWRS observer

c.  Tower visibility observer

d.  SAWRS observer

e.  A-paid observer

Definitions of these types are presented in paragraph 4-2, Definitions. Currency requirements are in Order 3120.4, Air Traffic Technical Training.

The METAR is the primary code format used in the United States to satisfy requirements for reporting surface meteorological data. The METAR may be prepared by automated weather observing systems (with or without augmentation) or by certified weather observers. These data are primarily reported in an alphanumeric coded format for aviation users. A complete METAR contains the type of report, station identifier, date/time of observation, and whether the report is automated (AUTO) or corrected (COR). Weather phenomena in the METAR include wind, visibility, runway visual range (RVR) (at designated sites), present weather, sky condition, temperature, dew point, and altimeter setting (collectively referred to as "the body of the report"). In addition, significant information elaborating on data reported in the body of the report, or coded and plain language data not included in the body of the report, may be appended to the report in a section referred to as "remarks." However, the content varies according to the type of weather station and the automated weather observing system used. (See Figure 15-1, Content of METAR/SPECI.) Many parts of the remarks section are not required at FAA facilities. The METAR is a scheduled observation. At manual stations, it is taken between 45 and 59 minutes past the hour. METARs are scheduled on the hour at ASOS sites and every 20 minutes at AWOS sites starting at H+00. A SPECI is an unscheduled observation taken when there is a significant change in the observation since the previous METAR observation was taken or if an aircraft mishap has occurred. If an aircraft mishap occurs close to a scheduled METAR, then it would be transmitted as a METAR. SPECI criteria are applicable only to stations that have the capability of evaluating the event. If it is time for a METAR to be issued, and SPECI observation criteria are met, the observation will remain designated as a METAR. SPECI observations are not issued at AWOS sites because METARs are issued every 20 minutes. (There are some rare exceptions to this rule.) The criteria for taking SPECI observations are given in Chapter 7, General Procedures for Manual Observations. Figure 2-1, Guide to Contents of Automated and Manual Aviation Routine Weather Reports (METAR) and Aviation Selected Special Weather (SPECI) Observations, summarizes the weather elements that are available at automated observing systems with precipitation discrimination capability (AO2), and those without precipitation discrimination capability (AO1). The precipitation discrimination capability indicator, AO1 or AO2, is included in the remarks section of the applicable METAR or SPECI report. This figure also shows the additional elements that are available when an observer is present to add information that is beyond the capabilities of the automated observing system (augmentation).

Figure 2-1. Guide to Contents of Automated and Manual Aviation Routine Weather Reports (METAR) and Aviation Selected Special Weather (SPECI) Observations (continued on next two tables below)

Figure 2-1. Guide to Contents of Automated and Manual Aviation Routine Weather Reports (METAR) and Aviation Selected Special Weather (SPECI) Observations (concluded from previous table)