AVIATION ROUTING WEATHER REPORT (METAR)

Observing Standards
Applicable to All
Stations.

a. Time used in Reports. With the exception of designated stations which transmit reports in accordance with agency instructions, METAR shall be transmitted at fixed intervals with SPECI transmitted when any of the criteria listed on page 4 (SPECI) occurs or is noted.

(1) Accuracy of Time in Reports. A procedure shall be established to assure that the accuracy of the timing device used to establish times in the observation program are within 1 minute of the Coordinated Universal Time as determined by the U.S. Naval Observatory.
(2) Scheduled Time of Report. The scheduled time of the METAR shall be the Coordinated Universal Time (UTC) a METAR is required to be available for transmission.
(3) Actual Date and Time of Observation. The actual date and time of METAR shall be the time the last element of the observation was observed. The actual time of a SPECI shall be the time the criteria for the SPECI was met or noted.
(4) Time Disseminated in Observations. All times disseminated in observations shall reference the 24-hour UTC clock; e.g., 1.47 A.M. shall be referred to as 0147 and 1:47 P.M. as 1347. The times 0000 and 2359 shall indicate the beginning and ending of the day, respectively.
(5) Date and Time entered in Observations. All dates and times entered in observations shall be with reference to the 24-hour clock. The times that are disseminated as part of the observation shall be entered in UTC. However, at the discretion of the responsible agency, those times used to otherwise document the observation or other related observational data may be either Local Standard Time (LST) or UTC. The time standard selected shall be clearly indicated on all records; if LST is used, the number of hours used to convert to UTC shall also be indicated.

4. Recency of Observed Elements at Automated Stations.

Individual elements entered in an observation shall, as closely as possible, reflect conditions existing at the actual time of observation. For those elements that the human observer evaluates using spatial averaging techniques (e.g., sky cover and visibility), the automated station substitutes time averaging of sensor data. Therefore, in an automated observation, sky condition shall be an evaluation of sensor data gathered during the 30-minute period ending at the actual time of the observation. All other elements shall be based on sensor data that is within 10 minutes or less of the actual time of the observation.

5. Recency of Observed Elements at Manual Stations.

Individual elements entered in an observation shall, as closely as possible, reflect conditions existing at the actual time of observation. Elements entered shall have been observed within 15 minutes of the actual time of the observation. Gusts and squalls shall be reported if observed within 10 minutes of the actual time of the observation. Observation of elements 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.

6. Corrections to Transmitted Data.

Corrections shall be disseminated, as soon as possible, whenever an error is detected in a transmitted report. However, if the erroneous data has been superseded by a later report (with the same or more complete dissemination), it shall not be necessary to transmit the corrected report. Corrections transmitted shall consist of the entire corrected report. The original date and time of the report.

7. Report Filing Time.

SPECIs shall be completed and transmitted as soon as possible. Agencies shall establish filing deadlines for all METARs. The filing deadlines shall be no sooner than necessary to assure the availability of the report at its scheduled time. METARs shall not be transmitted sooner than 10 minutes before their scheduled time.

8. Delayed Reports.

When transmission of an 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 FIBI (Filed But Impractical to Transmit) shall be appended in parentheses to the report that was not transmitted to indicate the report 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, the later SPECI 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 in the record of observations. The SPECI shall be disseminated locally.

Reports of Volcanic Eruption shall be disseminated, by any means possible, regardless of the delay.

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