This chapter prescribes procedures and practices applicable to all facilities and to all types of observations.

a.  Aircraft Mishap. Aircraft mishap is an inclusive term to denote the occurrence of an aircraft accident or incident.

b.  Coordinated Universal Time (UTC). UTC is the time in the zero degree meridian time zone, also commonly known as Zulu (Z) time.

c.  Local Standard Time (LST). LST is a time based on the geographic location of the facility in one of the legally established time zones of the globe.

d.  Standard Time of Observation. The standard time of observation is the hour to which a METAR observation applies.

e.  Aviation Routine Weather Report (METAR). A METAR is a measurement or evaluation of meteorological elements that describe the state of the atmosphere at the surface location(s) where the observation is taken. METAR is a scheduled observation.

f.  Aviation Selected Special Weather Report (SPECI). A SPECI is a weather observation that is reported at other than a scheduled time. SPECI shall be taken when any of the criteria for a special observation is observed or detected.

Surface weather observation locations shall make routine reports at fixed intervals (METAR reports). Where the capability exists, the routine reports shall be supplemented by non-routine reports (SPECI). The observing location is defined as the point or points at which the various elements are observed. In cases where all the measurements are taken at the same point, an observation will be regarded as having a single location. In cases where the various sensors are located to obtain acceptable exposure, the observation location will be regarded as varying with the individual elements in an observation. Normally, multiple observing points are confined to an area within about 2 miles of the station. Weather reports from manual stations may also contain information on phenomena occurring at other than the location of the observation. For example, at a large airport the observation location may be defined as follows:

a.  For elements such as clouds, prevailing visibility, present weather, and obscurations, the observing location may be coincident with the observer's physical location or it may be the touchdown area of the primary runway.

b.  For temperature, dew point, and wind, the observing location may be the center of the runway complex.

c.  For cloud height and ceiling, the observing location may be a point near the approach end of a runway.

d.  For the location of lightning, the observing point may be the Airport Reference Point (ARP). The ARP is a permanent airport reference point defined by a latitude/longitude.

e.  For tower visibility, the observing location shall be the Airport Traffic Control Tower (ATCT). (NA LAWRS)

f.  Regardless of observing location or the locations of the sensors, there shall be only one observation disseminated long-line for an airport. If applicable, a report from a commissioned ASOS shall be designated as the weather observation for that airport. A report from a commissioned AWOS may also be designated as the weather observation for an airport. When the air traffic control facility is not in operation, these systems will be operated in the fully automated mode as the weather observation source.

The general observing practices specified in the following subsections apply to personnel taking either full manual, augmented, backup, or tower visibility observations. They do not necessarily apply to the automated portions of observations, which are controlled by system software.

a.  Order of Observing. Elements having the greatest rate of change shall be evaluated last. When conditions are relatively unchanging, the observer shall evaluate the elements outdoors first, and then evaluate the elements indoors, with pressure being the last element evaluated.

b.  Recency of Observed Elements. Individual elements entered in an observation shall, as closely as possible, reflect conditions existing at the actual time of observation. At manual locations, elements entered shall have been observed within 15 minutes of the actual time of observation. Gusts and squalls shall be reported if observed within 10 minutes of the actual time of observation. METAR observations shall be made as close to the scheduled time of the observation as possible to meet filing deadlines, but in no case shall these observations be started more than 15 minutes before the scheduled time.

c.  Dark Adaptation. When taking observations outdoors at night, sufficient time should be allowed for the observer's eyes to become adjusted to the darkness.

d.  Weather Not Observed. Observers are not required to report occurrences they have not observed. However, the observer may use information from reliable sources, for example, pilots, airline/airport personnel or other sources deemed acceptable by the observer.

e.  Time Disseminated in Reports. All times shall refer to the 24-hour clock, for example, 1:47 a.m. shall be referred to as 0147; 1:47 p.m. shall be referred to as 1347. The times 0000 and 2359 shall be used to indicate the beginning and ending of the day, respectively.

f.  Time Standards. Times used in weather observations shall be:

(1)  Local Standard Time (LST). (NA LAWRS). LST is used on MF1M-10Cs to record times of observation and time checks. LST shall be entered on all forms throughout the year with no consideration of daylight savings time.

(2)  Coordinated Universal Time (UTC). UTC is used on all transmitted data. It is also used on MF1M-10Cs to record times of observations and time checks at LAWRS sites.

g.  Accuracy of Time in Observations. The accuracy of the actual time of observation and time checks on recording charts is very important in aviation safety investigations. One clock shall be designated as the observing location standard, and a routine procedure set up to assure its accuracy once a day at a minimum. The clock used shall be within ± 1 minute of the U.S. Naval Observatory Time. If available, the FAA Coded Time Source (CTS) may be substituted for U.S. Naval Observatory Time.

For purposes of this order, dissemination is the act of delivering a completed report to users. There are two general types of dissemination.

a.  Local. Local transmission is the transmission or delivery of a weather report to individuals or groups of users in the service area of the observing location.

b.  Long-line. Long-line transmission is the transmission of a weather report beyond the service area of the observing location.

All reports shall be given local dissemination. At designated stations, reports shall be given long-line dissemination. When reports are corrected, the corrected report shall be given the same dissemination as the report being corrected. If reports cannot be disseminated simultaneously, local and long-line, they shall be disseminated first to the local airport traffic control users, then disseminated long-line. SPECI observations shall be completed and transmitted as soon as possible after conditions meeting SPECI criteria are observed or detected. A METAR shall be transmitted in accordance with agency guidelines. A METAR entered that also meets the criteria for a SPECI shall be disseminated as a METAR. WS Form B-11, METAR/SPECI Report for Transmission, is available from the NWS for those facilities that receive manual observations from observers over the phone. This form is an optional aid for transcribing the observation for transmission. (See Appendix F, METAR/SPECI Report for Transmission.)

Once an error has been detected in a transmitted report, a correction shall be transmitted as soon as possible. Do not transmit a correction if the original transmitted observation has been superseded by a later report. Transmit the entire corrected report with (COR) as the report designator. Use the original date and time of the report being corrected.

When transmission of a manual observation is delayed until time for the next regularly scheduled report, only the latest report shall be transmitted. In the record of observations, the remark Filed But Impractical to Transmit (FIBI) shall be appended in parentheses to the report that was not transmitted. The remark FIBI shall not be included in any local dissemination of the report. When a SPECI is not transmitted long-line, later SPECIs shall be transmitted long-line only when the overall change between the last transmitted report and the current report satisfies the criteria for a SPECI. If the SPECI is not transmitted long-line, the remark FIBI shall be appended to the report as described above. All SPECI reports shall be disseminated locally. Reports of volcanic eruption shall be disseminated, by any means possible, regardless of the delay.

Except where otherwise designated in this order, when computations require that a number be rounded, if the fractional part of a positive number to be dropped is equal to or greater than one-half, the preceding digit shall be increased by one. If the fractional part of a negative number to be dropped is greater than one-half, the preceding digit shall be decreased by one. In all other cases, the preceding digit shall remain unchanged. For example, 1.5 becomes 2, 1.3 becomes 1, -1.5 becomes -1, and -2.6 becomes -3. Refer to paragraph 14-21, Rounding Pressure Values, for rounding of pressure values.

a.  Manual Observations. All manual observations, whether complete or partial, shall be recorded on form MF1M-10C (does not include automated stations). After completing the form, it shall be archived at the facility completing the form. Facilities shall prepare an original and at least one good duplicate copy of each form. The copies shall be legible and suitable for retention and duplication. Corrected copies of all forms shall be retained locally for 90 days. Retention of copies beyond 90 days shall be as directed by the Washington Headquarters. All original forms and the charts from recording instruments shall be mailed to the National Climatic Data Center (NCDC) as follows:

(1)  By the second working day of each month, mail all MF1M-10Cs for the preceding month, together with all recording charts except those from the ceilometer and transmissometer.

(2)  To facilitate handling and verification by NCDC, each day's form and recorder charts shall be placed in chronological order and shall be free of all staples.

Mail the original forms and recorder charts to:

NCDC Services Center
Image Entry
465 Industrial Blvd.
London, KY 40741

b.  Automated Weather Observations. Automated weather observations and operator terminal entries are archived on site. No further action is required by FAA, FAA-contract or NF-OBS facilities. In the event of a complete failure of automated equipment, observers are expected to follow manual observation recording requirements.

a.  Sensor Evaluations. When the observer has reason to believe that the accuracy or validity of indications from meteorological sensors is questionable, the use of such equipment should be discontinued until necessary corrective maintenance has been accomplished. If the use of such equipment is discontinued, any required back-up procedures or practices shall be initiated. FAA personnel and NF-OBS providers shall make appropriate maintenance notifications in the event of any equipment outages. If the observer believes that the ASOS information is inaccurate, they should notify the ASOS Operations and Monitoring Center (AOMC).

b.  Notices to Airmen (NOTAMS). The FSS/AFSS shall accept, categorize, and distribute Notices to Airmen (NOTAMs) on all systems and system components in accordance with the instructions contained in Order 7930.2.

c.  Time Entries on Recorder Charts. Time entries (such as those for time checks) on recorder charts shall be made to the nearest minute LST, except at LAWRS sites, where UTC time is entered.

d.  Time Checks on Recorder Charts. Time checks on the recorder chart of recording-type instruments shall be made as follows:

(1)  At the beginning and end of each chart roll.

(2)  When notified of an aircraft mishap.

(3)  For each disruption or discontinuity in the trace; e.g., upon return of equipment to service following an outage or periodic maintenance.

(4)  At the time of the first observation at facilities not operating 24 hours per day.

e.  Time Adjustments on Recorder Charts. When a recorder is adjusted to the correct time, the observer shall indicate the adjustment on the chart by entering an arrow at the point of the adjustment and writing the time of the adjustment near the arrow.

f.  Power and Equipment Failures. The observer shall indicate power and equipment failures on recording-type instruments by entering on the recorder chart at the point of the failure the term POWER FAILURE or EQUIPMENT FAILURE and the time of the failure. When the equipment is returned to service, the observer shall, if necessary, adjust the chart to the correct time and enter a time check.

An accurate Station Information File shall be maintained at the FAA regional headquarters. This file shall document the equipment (including automated weather observing systems equipment), instrumentation, and the observing program at the facility. The file shall contain, as a minimum, the information specified in the FMH-1 (see Figure 3-1). It is each region’s responsibility to ensure that a copy of the Station Information File for each observing location is sent to the National Climatic Data Center (NCDC), Attn: Code EF1100, of the National Oceanic and Atmospheric Administration (NOAA). A copy of the file shall be sent when a station is established, when any data listed in the file changes or is corrected, and when a station closes. This file shall become a part of that station’s archived record.