Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.1.3.10 Temperature/Dew Point Group
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
Temperature is the degree of hotness or coldness of the ambient air seems as measured by a suitable instrument. Dew point is the temperature to which a given parcel of air must be cooled at constant pressure and constant water vapor content for the air to become fully saturated.
Temperature and dew point are coded as two digits rounded to the nearest whole degree Celsius. For example, a temperature of 0.3ºC would be coded at 00. Sub-zero temperatures and dew points are prefixed with an M. For example, a temperature of 4ºC with a dew point of – 2ºC would be coded as 04/M02; a temperature of –2ºC would be coded as M02.
If temperature is not available, the entire temperature/dew point group is not coded. If dew point is not available, temperature is coded followed by a solidus, /, and no entry made for dew point.
For example, a temperature of 1.5ºC and a missing dew point would be coded as 02/.
3.1.3.11 Altimeter
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
The altimeter setting group codes the current pressure at elevation. This setting is then used by aircraft altimeters to determine the true altitude above a fixed plane of mean sea level.
The altimeter group always starts with an A (the international indicator for altimeter in inches of mercury) and is followed by the four digit group representing the pressure in tens, units, tenths, and hundredths of inches of mercury. The decimal point is not coded. For example, an altimeter setting of 29.92 inches of Mercury would be coded as A2992.
3.1.3.12 Remarks (RMK)
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
Remarks are included in all METAR and SPECI, when appropriate.
Remarks are separated from the body of the report by the contraction RMK. When no remarks are necessary, the contraction RMK is not required.
METAR/SPECI remarks fall into two categories: (1) Automated, Manual, and Plain Language, and (2) Additive Maintenance Data.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Table 3-5. METAR/SPECI Order of Remarks Automated, Manual, and Plain Language Additive and Automated Maintenance Data
1. Volcanic Eruptions 14. Hailstone Size 27. Precipitation*
2. Funnel Cloud 15. Virga 28. Cloud Types*
3. Type of Automated Station 16. Variable Ceiling Height 29. Duration of Sunshine*
4. Peak Wind 17. Obscurations 30. Hourly Temperature and Dew Point
5. Wind Shift 18. Variable Sky Condition 31. 6-Hourly Maximum Temperature*
6. Tower or Surface Visibility 19. Significant Cloud Types 32. 6-Hourly Minimum Temperature*
7. Variable Prevailing Visibility 20. Ceiling Height at Second Location 33. 24-Hour Maximum and Minimum Temperature*
8. Sector Visibility 21. Pressure Rising or Falling Rapidly 34. 3-Hourly Pressure Tendency*
9. Visibility at Second Location 22. Sea-Level Pressure 35. Sensor Status Indicators
10. Lightning 23. Aircraft Mishap 36. Maintenance Indicator
11.
Beginning and Ending of Precipitation
24. No SPECI Reports Taken Note: Additive data is primarily used by the National Weather Service for climatological purposes.
* These groups should have no direct impact on the aviation community and will not be discussed in this document.
12.
Beginning and Ending of Thunderstorms
25. Snow Increasing Rapidly
13. Thunderstorm Location 26. Other Significant Information
Remarks are made in accordance with the following:
• Time entries are made in minutes past the hour if the time reported occurs during the same hour the observation is taken. Hours and minutes are used if the hour is different;
• Present weather coded in the body of the report as VC may be further described, i.e., direction from the station, if known. Weather phenomena beyond 10 statute miles of the point(s) of observation are coded as distant (DSNT) followed by the direction from the station. For example, precipitation of unknown intensity within 10 statute miles east of the station would be coded as VCSH E; lightning 25 statute miles west of the station would be coded as LTG DSNT W;
• Distance remarks are in statute miles except for automated lightning remarks which are in nautical miles;
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
• Movement of clouds or weather, when known, is coded with respect to the direction toward which the phenomena are moving. For example, a thunderstorm moving toward the northeast would be coded as TS MOV NE;
• Directions use the eight points of the compass coded in a clockwise order; and
• Insofar as possible, remarks are entered in the order they are presented in the following paragraphs (and Table 3-5).
3.1.3.13 Automated, Manual, and Plain Language Remarks These remarks generally elaborate on parameters reported in the body of the report.
Automated and manual remarks may be generated either by an automated station or observer.
Plain language remarks are only provided from an observer.
3.1.3.13.1 Volcanic Eruptions (Plain Language) Volcanic eruptions are coded in plain language and contain the following, when known:
• Name of volcano
• Latitude and longitude or the direction and approximate distance from the station
• Date/Time (UTC) of the eruption
• Size description, approximate height, and direction of movement of the ash cloud
• Any other pertinent data about the eruption
For example, a remark on a volcanic eruption would look like the following:
MT. AUGUSTINE VOLCANO 70 MILES SW ERUPTED AT 231505 LARGE ASH CLOUD EXTENDING TO APRX 30000 FEET MOVING NE.
Pre-eruption volcanic activity is not coded. Pre-eruption refers to unusual and/or increasing volcanic activity which could presage a volcanic eruption.
3.1.3.13.2 Funnel Cloud At manual stations, tornadoes, funnel clouds, and waterspouts are coded in the following format: Tornadic activity, TORNADO, FUNNEL CLOUD, or WATERSPOUT, followed by the beginning and/or ending time, followed by the location and/or direction of the phenomena from the station, and/or movement, when known. For example, TORNADO B13 6 NE would indicate that a tornado began at 13 minutes past the hour and was 6 statute miles northeast of the station.
3.1.3.13.3 Type of Automated Station AO1 or AO2 are coded in all METAR/SPECI from automated stations. Automated stations without a precipitation discriminator are identified as AO1; automated stations with a precipitation discriminator are identified as AO2.
3.1.3.13.4 Peak Wind Peak wind is coded in the following format: the remark identifier PK WND, followed by the direction of the wind (first three digits), peak wind speed (next two or three digits) since the last METAR, and the time of occurrence. A space is between the two elements of the remark identifier and the wind direction/speed group; a solidus, /, (without spaces) separates the wind AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-17
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) direction/speed group and the time. For example, a peak wind of 45 knots from 280 degrees which occurred at 15 minutes past the hour is coded PK WND 28045/15.
3.1.3.13.5 Wind Shift Wind shift is coded in the format: the remark identifier WSHFT, followed by the time the wind shift began. The contraction FROPA is entered following the time if there is reasonable data to consider the wind shift was the result of a frontal passage. A space is between the remark identifier and the time and, if applicable, between the time and the frontal passage contraction.
For example, a remark reporting a wind shift accompanied by a frontal passage that began at 30 minutes after the hour would be coded as WSHFT 30 FROPA.
3.1.3.13.6 Tower or Surface Visibility Tower or surface visibility is coded in the following format: tower TWR VIS or surface SFC, followed by the observed tower/surface visibility value. A space is coded between each of the remark elements. For example, the control tower visibility of 1 ½ statute miles would be coded TWR VIS 1 1/2.
3.1.3.13.7 Variable Prevailing Visibility Variable prevailing visibility is coded in the following format: the remark identifier VIS, followed the lowest and highest visibilities evaluated separated by the letter V. A space follows the remark identifier and no spaces are between the letter V and the lowest/highest values. For example, a visibility that was varying between 1/2 and 2 statute miles would be coded VIS 1/2V2.
3.1.3.13.8 Sector Visibility (Plain Language) Sector visibility is coded in the following format: the remark identifier VIS, followed by the sector referenced to 8 points of the compass, and the sector visibility in statute miles. For example, a visibility of 2 1/2 statute miles in the northeastern octant is coded VIS NE 2 1/2.
3.1.3.13.9 Visibility at Second Location At designated automated stations, the visibility at a second location is coded in the following format: the remark identifier VIS, followed by the measured visibility value and the specific location of the visibility sensor(s) at the station. This remark will only be generated when the condition is lower than that contained in the body of the report. For example, a visibility of 2 1/2 statute miles measured by a second sensor located at runway 11 is coded VIS 2 1/2 RWY11.
3.1.3.13.10 Lightning When lightning is observed at a manual station, the frequency, type of lightning and location is reported. The contractions for the type and frequency of lightning are based on Table 3-6, for example, OCNL LTGICCG NW, FRQ LTG VC, or LTG DSNT W.
When lightning is detected by an automated system:
• Within 5 nautical miles of the Airport Location Point (ALP), it is reported as TS in the body of the report with no remark;
• Between 5 and 10 nautical miles of the ALP, it is reported as VCTS in the body of the report with no remark; and
• Beyond 10 but less than 30 nautical miles of the ALP, it is reported in remarks only as LTG DSNT followed by the direction from the ALP.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Table 3-6. METAR/SPECI Type and Frequency of Lightning Type of Lightning Type Contraction Definition Cloud-ground CG Lightning occurring between cloud and ground.
In-cloud IC Lightning which takes place within the cloud.
Cloud-cloud CC Streaks of lightning reaching from one cloud to another.
Cloud-air CA Streaks of lightning which pass from a cloud to the air, but do not strike the ground.
Frequency of Lightning Frequency Contraction Definition Occasional OCNL Less than 1 flash/minute.
Frequent FRQ About 1 to 6 flashes/minute.
Continuous CONS More than 6 flashes/minute.
3.1.3.13.11 Beginning and Ending of Precipitation At designated stations, the beginning and ending time of precipitation is coded in the following format: the type of precipitation, followed by either a B for beginning or an E for ending, and the time of occurrence. No spaces are coded between the elements. The coded times of the precipitation start and stop times are found in the remarks section of the next METAR. The times are not required to be in the SPECI. The intensity qualifiers are coded. For example, if rain began at 0005 and ended at 0030 and then snow began at 0020 and ended at 0055, the remarks would be coded as RAB05E30SNB20E55. If the precipitation were showery, the remark is coded SHRAB05E30SHSNB20E55. If rain ended and snow began at 0042, the remark would be coded as RAESNB42.
3.1.3.13.12 Beginning and Ending of Thunderstorms The beginning and ending of thunderstorms are coded in the following format: TS for thunderstorms, followed by either a B for beginning or an E for ending and the time of occurrence. No spaces are between the elements. For example, if a thunderstorm began at 0159 and ended at 0230, the remark is coded TSB0159E30.
3.1.3.13.13 Thunderstorm Location (Plain Language) Thunderstorm locations are coded in the following format: the thunderstorm identifier, TS, followed by location of the thunderstorm(s) from the station and the direction of movement when known. For example, a thunderstorm southeast of the station and moving toward the northeast is coded TS SE MOV NE.
3.1.3.13.14 Hailstone Size (Plain Language) At designated stations the hailstone size is coded in the following format: the hail identifier GR, followed by the size of the largest hailstone. The hailstone size is coded in ¼ inch increments.
For example, GR 1 3/4 would indicate that the largest hailstone were 1 ¾ inches in diameter. If small hail or snow pellets, GS, is coded in the body of the report, no hailstone size remark is required.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.1.3.13.15 Virga (Plain Language) Virga is coded in the following format: the identifier VIRGA, followed by the direction from the station. The direction of the phenomena from the station is optional, e.g., VIRGA or VIRGA SW.
3.1.3.13.16 Variable Ceiling Height The variable ceiling height is coded in the following format: the identifier CIG, followed by the lowest ceiling height recorded, V denoting variability between two values, and ending with the highest ceiling height. A single space follows the identifier with no other spaces between the letter V and the lowest/highest ceiling values. For example, CIG 005V010 would indicate a ceiling is variable between 500 and 1,000 feet.
3.1.3.13.17 Obscurations (Plain Language) Obscurations, surface-based or aloft, are coded in the following format: the weather identifier causing the obscuration at the surface or aloft followed by the sky cover of the obscuration aloft (FEW, SCT, BKN, OVC) or at the surface (FEW, SCT, BKN), and the height. Surface-based obscurations have a height of 000. A space separates the weather causing the obscuration and the sky cover; no space is between the sky cover and the height. For example, fog hiding 3/8 to 4/8 of the sky is coded FG SCT000; a broken layer at 2,000 feet composed of smoke is coded FU BKN020.
3.1.3.13.18 Variable Sky Condition (Plain Language) Variable sky condition remarks are coded in the following format: the two operationally significant sky conditions (FEW, SCT, BKN, and OVC) separated by spaces and V denoting the variability between the two ranges. If several layers have the same condition amount, the layer height of the variable layer is coded. For example, a cloud layer at 1,400 feet varying between broken and overcast is coded BKN014 V OVC.
3.1.3.13.19 Significant Cloud Types (Plain Language) Significant cloud type remarks are coded in all reports.
3.1.3.13.19.1 Cumulonimbus or Cumulonimbus Mammatus Cumulonimbus or Cumulonimbus Mammatus not associated with thunderstorms are coded in the following format: the cloud type (CB or CBMAM) followed by the direction from the station and the direction of movement when known. The cloud type, location, direction, and direction of movement entries are separated from each other by a space. For example, a CB up to 10 statute miles west of the station moving toward the east would be coded CB W MOV E. If the CB was more than 10 statute miles to the west, the remark is coded CB DSNT W.
Cumulonimbus (CB) always evolves from the further development of towering cumulus (TCU).
The unusual occurrence of lightning and thunder within or from a CB leads to its popular title, thunderstorm. A thunderstorm usually contains severe or greater turbulence, severe icing, low level wind shear (LLWS), and instrument flight rules (IFR) conditions.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 3-5. Cumulonimbus (CB) Example CB always evolves from the further development of towering cumulus (TCU). The usual occurrence of lightning and thunder within or from a CB leads to its popular title, thunderstorm. A thunderstorm usually contains severe or greater turbulence, severe icing, low level wind shear (LLWS), and instrument flight rules (IFR) conditions. (Copyright Robert A. Prentice, 1990)
Figure 3-6. Cumulonimbus Mammatus (CBMAM) Example Cumulonimbus Mammatus (CBMAM) (also called mammatus) appears as hanging protuberances, like pouches, on the undersurface of a cloud. (Copyright Robert A. Prentice, 1993) AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-21
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.1.3.13.19.2 Towering Cumulus Towering cumulus clouds are coded in the following format: the identifier TCU followed by the direction from the station. The cloud type and direction entries are separated by a space. For example, a towering cumulus cloud up to 10 statute miles west of the station is coded as TCU W.
Figure 3-7. Towering Cumulus (TCU) Example Towering Cumulus (TCU). TCU is produced by strong convective updrafts and, thus, indicates turbulence.
Icing is typically found above the freezing level. TCU often transforms into cumulonimbus (CB). (Copyright Charles A. Doswell, III, 1977)
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.1.3.13.19.3 Altocumulus Castellanus Altocumulus Castellanus is coded in the following format: the identifier ACC followed by direction from the station. The cloud type and direction entries are separated by a space. For example, an altocumulus cloud 5 to 10 statute miles northwest of the station is coded ACC NW.
Figure 3-8. Altocumulus Castellanus (ACC) Example Altocumulus Castellanus (ACC). ACC indicates convective turbulence aloft from the top of the cloud to its base and usually an undetermined height below cloud base as well. (Photo courtesy of National Severe Storms Laboratory/University of Oklahoma)
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.1.3.13.19.4 Standing Lenticular or Rotor Clouds Stratocumulus (SCSL), altocumulus (ACSL), or cirrocumulus (CCSL), or rotor clouds are coded in the following format: the cloud type followed by the direction from the station. The cloud type and direction entries are separated by a space. For example, altocumulus standing lenticular clouds observed southwest through west of the station are coded ACSL SW-W; an apparent rotor cloud 5 to 10 statute miles northeast of the station is coded APRNT ROTOR CLD NE; and cirrocumulus clouds south of the station are coded CCSL S.
Figure 3-9. Standing Lenticular and Rotor Clouds Example From top to bottom: Cirrocumulus standing lenticular (CCSL), altocumulus standing lenticular (ACSL), and rotor cloud. These clouds are characteristic of mountain waves. Mountain waves can occasionally produce violent downslope windstorms. Intense mountain waves can present a significant hazard to aviation by producing severe or even extreme turbulence that extends upward into the lower stratosphere.
3.1.3.13.20 Ceiling Height at Second Location At designated stations, the ceiling height at a second location is coded in the following format:
the identifier CIG followed by the measured height of the ceiling and the specific location of the ceilometer(s) at the station. This remark is only generated when the ceiling is lower than that contained in the body of the report. For example, if the ceiling measured by a second sensor located at runway 11 is broken at 200 feet, the remark would be CIG 002 RWY11.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.1.3.13.21 Pressure Rising or Falling Rapidly At designated stations, the reported pressure is evaluated to determine if a pressure change is occurring. If the pressure is rising or falling at a rate of at least 0.06 inch per hour and the pressure change totals 0.02 inch or more at the time of the observation, a pressure change remark is reported. When the pressure is rising or falling rapidly at the time of observation, the remark PRESRR (pressure rising rapidly) or PRESFR (pressure falling rapidly) is included in the remarks.
3.1.3.13.22 Sea-Level Pressure At designated stations, the sea-level pressure is coded in the following format: the identifier SLP immediately followed by the sea level pressure in hectopascals. The hundreds and thousands units are not coded and must be inferred. For example, a sea-level pressure of
998.2 hectopascals is coded as SLP982. A sea-level pressure of 1013.2 hectopascals would be coded as SLP132. For a METAR, if sea-level pressure is not available, it is coded as SLPNO.
3.1.3.13.23 Aircraft Mishap (Plain Language) If a SPECI report is taken to document weather conditions when notified of an aircraft mishap, the remark ACFT MSHP is coded in the report but the SPECI not transmitted.
3.1.3.13.24 No SPECI Reports Taken (Plain Language) At manual stations where SPECIs are not taken, the remark NOSPECI is coded to indicate no changes in weather conditions will be reported until the next METAR.
3.1.3.13.25 Snow Increasing Rapidly At designated stations, the snow increasing rapidly remark is reported, in the NEXT METAR, whenever the snow depth increases by 1 inch or more in the past hour. The remark is coded in the following format: the remark indicator SNINCR, the depth increase in the past hour, and the total depth of snow on the ground at the time of the report. The depth of snow increase in the past hour and the total depth on the ground are separated from each other by a solidus, /. For example, a snow depth increase of 2 inches in the past hour with a total depth on the ground of 10 inches is coded SNINCR 2/10.
3.1.3.13.26 Other Significant Information (Plain Language) Agencies may add to a report other information significant to their operations, such as information on fog dispersal operations, runway conditions, FIRST or LAST reports from station, etc.
3.1.3.14 Additive and Automated Maintenance Data Additive data groups (Table 3-5) are only reported at designated stations and are primarily used by the NWS for climatological purposes. Most have no direct impact on the aviation community but a few are discussed below.
3.1.3.14.1 Hourly Temperature and Dew Point At designated stations, the hourly temperature and dew point group are further coded to the tenth of a degree Celsius. For example, a recorded temperature of +2.6ºC and dew point of -1.5ºC would be coded as T00261015.
The format for the coding is as follows:
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) T Group indicator 0 Indicates the following number is positive; a 1 would be used if the temperature was reported as negative at the time of observation 026 Temperature disseminated to the nearest 10 th and read as 02.6 1 Indicates the following number is negative; a 0 would be used if the number was reported as positive at the time of observation 015 Dew Point disseminated to the nearest 10th and read as 01.5
No spaces are between the entries. For example, a temperature of 2.6ºC and dew point of –
1.5ºC is reported in the body of the report as 03/M01 and the hourly temperature and dew point group as T00261015. If the dew point is missing only the temperature is reported; if the temperature is missing the hourly temperature and dew point group is not reported.
3.1.3.14.2 Maintenance Data Groups The following maintenance data groups, Sensor Status Indicators and the Maintenance Indicator, are only reported from automated stations.
3.1.3.14.2.1 Sensor Status Indicators Sensor status indicators are reported as indicated below:
• If the Runway Visual Range is missing and would normally be reported, RVRNO is coded
• When automated stations are equipped with a present weather identifier and the sensor is not operating, the remark PWINO is coded
• When automated stations are equipped with a tipping bucket rain gauge and the sensor is not operating, PNO is coded
• When automated stations are equipped with a freezing rain sensor and the sensor is not operating, the remark FZRANO is coded
• When automated stations are equipped with a lightning detection system and the sensor is not operating, the remark TSNO is coded
• When automated stations are equipped with a secondary visibility sensor and the sensor is not operating, the remark VISNO LOC is coded
• When automated stations are equipped with a secondary ceiling height indicator and the sensor is not operating, the remark CHINO LOC is coded
3.1.3.14.2.2 Maintenance Indicator A maintenance indicator, $, is coded when an automated system detects maintenance is needed on the system.
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