The following are minimum requirements for equipment required to provide the weather information specified in this chapter. Unless stated otherwise, the equipment is required only if that element is required at your facility. References to an "OID/OT" indicate any automated weather observing system operator interface device.

a.  Equipment for Wind Direction and Speed. If available, the primary low-level wind shear alert system (LLWAS) sensor or other on-site wind equipment shall be used. Otherwise, the wind direction and speed may be estimated during periods when all automated wind sensors are inoperative.

b.  Equipment for Visibility. There is no equipment required for automated visibility sensor backup. However, a current list or visibility chart(s) depicting day and night visibility reference points shall be maintained and available at the point of observation for use at each facility.

c.  Equipment for Present Weather and Obstructions to Vision. Visual procedures shall be used to identify the type(s) of present weather and/or obscurations. If necessary, visual procedures shall be used to determine the intensity of precipitation.

d.  Equipment for Sky Condition. There is no equipment required for automated sky condition sensor backup. If independent cloud height equipment is available, it should be used to obtain cloud height information. If such equipment is not available, visual estimates shall be made. Pilot reports of cloud heights may be used if available.

e.  Equipment for Temperature and Dew Point. A remote readout hygrothermometer is an acceptable backup for temperature and dew point. Other acceptable backups are a sling psychrometer, a battery-operated self-contained psychrometer, or a stand-alone temperature measuring device, as approved by FAA.

f.  Equipment for Altimeter Setting. Equipment to back up altimeter setting may be any FAA installed and maintained altimeter setting indicator (ASI) or digital altimeter setting indicator (DASI), or any other facility station pressure instrument, with certification and calibration traceable to the National Institute of Standards and Technology as defined in FAA Order 7210.3, Facility Operation and Administration.

g.  Equipment for OID/OT. If the ASOS OID fails, and the ASOS observation is currently representative, the observer shall continue to maintain oversight of the ASOS through the use of other ASOS displays (e.g., Video Display Unit (VDU)) and shall make appropriate maintenance notifications. If significant weather is occurring or expected to occur, after coordinating with ATCT, arrange, through appropriate maintenance channels, for local and long-line communications to be disabled. Notify on-site users that have ASOS displays to turn off power to their display. Provide backup observations.

h.  Equipment for Communications. No additional equipment is required for the communication of backup weather information. If the primary communications equipment is unavailable, any appropriate communications media may be used. When long-line communications are unavailable, request that weather information be disseminated by the FSS/AFSS.

i.  Equipment Requirements for NF-OBS Providers. The NF-OBS provider shall provide and maintain all backup equipment. The cost of procuring, installing, operating, moving (if required), protecting and maintaining all instruments and equipment in accordance with FAA and NWS specifications is to be borne by the provider. The OID, which is part of the ASOS, will be maintained and serviced by the Government.

General observer procedures for providing required backup information are summarized in Figure 4-1, Operator Procedures for Providing Augmentation and Backup Information. At ASOS sites, required weather data elements shall be entered into the automated weather observing system using the editing procedures for the automated weather observing system operator interface device. At AWOS sites, entry of data shall be as specified in the AWOS Operators Instructions or the appropriate FAA approved AWOS manufacturer's equipment manual. For non-representative data, the observer may turn report processing off (ASOS) or set the channel out of service (AWOS). The turning off of report processing will lead to a "$" sign, and the generation of a trouble ticket for the NWS ASOS Operations and Monitoring Center (AOMC). Observers shall not turn off report processing for altimeter setting without appropriate maintenance notification. Once the report processing for the altimeter setting is turned off, only an NWS technician can turn the report processing back on.

If any element, normally included in the body of the observation, except present weather and obscurations, is missing because of sensor failure, and that element is not required for backup, that element may be omitted. If the automated weather observing system's processor is operative, the system will do this automatically. If not operative, these missing elements shall be omitted and skipped over. When an element or phenomena does not occur, or cannot be observed, the corresponding group and preceding space are omitted from that particular report.

General procedures for the reporting of backup information for visibility are given in Figure 6-4, Backup Reporting of Tower/Surface Visibility. The visibility shall be a prevailing visibility. (Note: RVR is not addressed here because it will not be backed up by FAA controllers (including LAWRS).)

a.  Reporting Visibility Values. In backing up visibility, the reportable values for visibility shall be the manual visibility values as permitted by the current system software installed; see Figure 9-1, Reportable Visibility Values. If the actual visibility falls between two reportable values, the lower value shall be reported.

b.  Tower Visibility During Backup (with Surface Observer). During backup periods at towered facilities with a surface-based observer, the responsible tower controller shall:

(1)  Notify the surface-based observer when the tower prevailing visibility is observed to decrease to less than, or if below, increases to equal or exceed, 4 miles.

(2)  Report all changes of one or more reportable values to the surface-based observer when the prevailing visibility at the tower or the surface is less than 4 miles.

(3)  As required by FAA directives, use the lower of either the tower or weather station visibility as controlling visibility for aircraft operations.

Figure 6-5. Backup Reporting of Weather Phenomena

General procedures for the reporting of backup information for present weather and obscurations are given in Figure 6-5, Backup Reporting of Weather Phenomena. Present weather and obscurations to vision shall be observed and reported in accordance with the manual procedures prescribed in Chapter 11, Weather Phenomena. Reports shall include as a minimum those weather phenomena in Figure 6-6, Backup and Augmentation Weather and Obscurations, when backing up ASOS. (If the observer is backing up ASOS at the close of augmentation/
backup coverage, it will be necessary to end the event or it will continue to be reported during the hours when there is no augmentation/backup coverage.) Precipitation of unknown form is generally only reported when the automated weather observing system present weather indicator sensor is operational and is reporting precipitation of unknown form. However, if the observer can determine the type of precipitation, it should be reported according to the guidelines in Figure 6-6, via the non-representative data procedures.

General procedures for the reporting of backup weather information for sky condition are given in Figure 6-7, Backup Reporting of Sky Condition. More details on procedures for observing sky condition are included in Chapter 12, Sky Condition. If required, the following procedures for reporting sky condition shall apply:

a.  Reporting Procedures.

(1)  Report sky cover up to 12,000 feet, or as specified in the designated service level standard, whichever is greater. (See Appendix D, Service Standards.)

(2)  Non-opaque cloud layers shall be treated as opaque and reported.

(3)  No more than three layers shall be reported, and

(4)  "CLR" (clear) shall be reported at an automated site when no clouds are visible up to 12,000 feet, or as specified in the designated service level standard, whichever is greater.

b.  Sky Cover. Sky cover is any clouds or obscuring phenomena aloft detected from the observing location. It shall be evaluated with reference to the surface. All clouds or obscuring phenomena aloft shall be considered opaque sky cover.

c.  Sky Condition Evaluation. Evaluation of sky condition shall include the amount and height of cloud bases up to 12,000 feet, or as specified in the designated service level standard, whichever is greater.

d.  Reporting Ceiling. The lowest layer that is reported as broken or overcast shall be the ceiling. If the sky is totally obscured, the height of the vertical visibility shall be the ceiling.

e.  Vertical Visibility. Vertical visibility shall be either:

(1)  The distance that an observer can see vertically into a surface-based obscuring phenomenon.

(2)  The height corresponding to the top of a ceiling light projector beam.

(3)  The height at which a balloon completely disappears during the presence of a surface-based obscuring phenomenon.

(4)  The height determined by the sensor algorithm at an automated station.

f.  Obscuration. The portion of sky (including higher clouds, the moon, or stars) hidden by weather phenomena either surface-based or aloft. At designated stations, obscurations are indicated in the remarks of the report.

g.  Number of Layers Reported. Automated weather observing stations shall report no more than three layers of clouds or one layer for an obscuring phenomena. Manual weather observing stations shall report no more than six layers. If multiple cloud layers are observed below 12,000 feet, up to three layers shall be reported in accordance with the priorities in Figure 6-8, Priority for Reporting Cloud Layers.

Figure 6-8. Priority for Reporting Cloud Layers

h.  Height of Layers. The height of a layer is the height of the cloud bases or obscurations of the layer being evaluated. Layers of clouds that are 50 feet or less above the surface shall be observed as layers with a height of zero (000). When the height of a ceiling layer increases and decreases rapidly by the amounts given in Figure 6-9, Criteria for Variable Ceiling, during the period of evaluation, it shall be considered variable and the ascribed height shall be the average of all the values. When the height of the ceiling layer is variable and the reported ceiling is below 3,000 feet, a remark shall be added, for example, CIG 010V016.

Figure 6-9. Criteria for Variable Ceiling

i.  Height of Sky Cover. If available, a ceilometer or ceiling light, or known heights of unobscured portions of abrupt, isolated objects within 1 1/2 miles of the point of observation shall be used to measure the height of layers aloft or the vertical visibility into obscuring phenomena. Otherwise, an alternative method shall be used to estimate the height. The height may be estimated by using a ceiling balloon, pilot report, or observer experience (visual estimate).

j.  Reportable Values for Sky Cover Height. Heights of layers shall be reported in hundreds of feet above the surface, rounded to the nearest reportable increment given in Figure 6-10, Increments of Reportable Values of Sky Cover Height. When a value falls halfway between two reportable increments, the lower value shall be reported. When a cloud is 50 feet or less above the surface, the height shall be reported as 000.

Figure 6-10. Increments of Reportable Values of Sky Cover Height

k.  Layer Amounts. The amount of sky cover for each layer is the eighths of sky cover attributable to the clouds in the layer being evaluated. The report shall be based on each layer in combination with any lower layers. The amount of sky cover reported for each layer shall be based on the summation amount for that layer and shall be reported using the reportable values given in Figure 6-11, Reportable Contractions for Sky Cover Amount. The summation amount of sky cover for any given layer is the sum of the sky cover of the layer being evaluated, plus the sky cover of all lower layers. Portions of layers aloft detected through lower layers aloft shall not increase the summation amount of the higher layer. No layer can have a summation amount greater than 1.0 (8/8ths).

Figure 6-11. Reportable Contractions for Sky Cover Amount

General procedures for the reporting of backup information for temperature and dew point are given in Figure 6-12, Backup Reporting of Temperature and Dew Point. If either the temperature module, dew point module, or both of the automated weather observing system are inoperative, both the temperature and dew point shall be reported from other equipment as specified in paragraph 6-4, Equipment Requirements.

a.  Units of Measure. The units of measure for temperature and dew point are degrees Celsius. Dew point shall be calculated with respect to water at all temperatures.

b.  Reporting Procedures for Temperature. The temperature shall be entered as two digits to the nearest whole degree Celsius. Sub-zero temperatures shall be prefixed with an M (minus). For example, a temperature of 4 degrees Celsius with a dew point of -2 degrees Celsius is coded as 04/M02. See paragraph 3-9, Rounding Off Numbers, for rounding off procedures. A temperature of -0.5^oC shall be reported as M00 to indicate that the actual temperature is below zero but rounded to zero.

c.  Reporting Procedures for Dew Point. The dew point temperature shall be entered as two digits to the nearest whole degree Celsius. Sub-zero dew point temperatures shall be prefixed with an M. When the dry-bulb temperature is -34.4°C or below, the dew point shall be reported as unavailable. For example, when the temperature is -36, it will be reported as M36/.

Figure 6-12. Backup Reporting of Temperature and Dew Point

General procedures for the reporting of backup information for altimeter setting are given in Figure 6-2, Backup Reporting of Wind or Altimeter Setting. The observer shall use any FAA installed and maintained altimeter setting indicator (ASI) or digital altimeter setting indicator (DASI), or any other altimeter setting source approved by the FAA that meets altimeter and comparison check requirements of the latest version of Order 7210.3, Facility Operation and Administration.

If the automated weather observing system is unable to document the observational data, the data shall be recorded on Meteorological Form 1M-10C (MF1M-10C).  This only applies to a complete failure of the system. See Chapter 16, Entries on Observational Forms, for details.

Each facility shall establish procedures for local distribution of backup weather data in the event that the automated weather observing system's local communications are out of service.

MF1M-10C forms shall be handled in accordance with procedures specified in paragraph 3-10, Record Keeping and Forms.

Examples of backup weather observations for a typical condition (i.e., ceilometer and anemometer not operational) are given for AWOS and ASOS in Figure 6-13, AWOS Backup Observation Examples, and Figure 6-14, ASOS Backup Observation Examples.

6-17.   MALFUNCTIONS/OUTAGES

Automated weather observing systems have a self-monitoring capability. The systems will discontinue reporting the affected weather element when a given weather sensor is out of tolerance or fails. FAA personnel and NF-OBS providers shall make appropriate maintenance notifications in the event of any equipment outages. Information on the issuance of NOTAMs is contained in Order 7930.2.