Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Table 3-2. METAR/SPECI Notations for Reporting Present Weather1
QUALIFIER WEATHER PHENOMENA
INTENSITY OR
PROXIMITY
DESCRIPTOR PRECIPITATION OBSCURATION OTHER 1 2 3 4 5
- Light MI Shallow DZ Drizzle BR Mist PO Dust/Sand whirls
Moderate2 PR Partial RA Rain FG Fog SQ Squalls
+ Heavy BC Patches SN Snow FU Smoke FC Funnel Cloud, Tornado, or Waterspout4
VC In the Vicinity3 DR Low Drifting SG Snow Grains VA Volcanic Ash SS Sandstorm BL Blowing IC Ice Crystals (Diamond Dust)
DU Widespread Dust DS Duststorm SH Shower(s) PL Ice Pellets SA Sand
TS Thunderstorms GR Hail HZ Haze
FZ Freezing GS Small Hail and/or Snow Pellets
PY Spray UP Unknown Precipitation
1. The weather groups are construct ed by considering columns 1 to 5 in the table above in sequence,
i.e., intensity followed by description, followed by weather phenomena, e.g., heavy rain shower(s) is coded as +SHRA.
2. To denote moderate intensity no entry or symbol is used.
3. See text for vicinity definitions.
4. Tornadoes and waterspouts are coded as +FC.
Separate groups are used for each type of present weather. Each group is separated from the other by a space. METAR/SPECI reports contain no more than three present weather groups.
When more than one type of present weather is reported at the same time, present weather is reported in the following order:
• Tornadic activity – Tornado, Funnel Cloud, or Waterspout.
• Thunderstorm(s) with and without associated precipitation.
• Present weather in order of decreasing dominance, i.e., the most dominant type is reported first.
• Left-to-right in Table 3-2 (Columns 1 through 5).
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Qualifiers may be used in various combinations to describe weather phenomena. Present weather qualifiers fall into two categories: intensity (Section 3.1.3.8.1) or proximity (Section
3.1.3.8.2) and descriptors (Section 3.1.3.8.3).
3.1.3.8.1 Intensity Qualifier The intensity qualifiers are light, moderate, and heavy. They are coded with precipitation types except ice crystals (IC) and hail (GR or GS) including those associated with a thunderstorm (TS) and those of a showery nature (SH). Tornadoes and waterspouts are coded as heavy (+FC).
No intensity is ascribed to the obscurations of blowing dust (BLDU), blowing sand (BLSA), and blowing snow (BLSN). Only moderate or heavy intensity is ascribed to sandstorm (SS) and duststorm (DS).
When more than one form of precipitation is occurring at a time or precipitation is occurring with an obscuration, the reported intensities are not cumulative. The reported intensity will not be greater than the intensity for each form of precipitation.
3.1.3.8.2 Proximity Qualifier Weather phenomena occurring beyond the point of observation (between 5 and 10 statute miles) are coded as in the vicinity (VC). VC can be coded in combination with thunderstorm (TS), fog (FG), shower(s) (SH), well-developed dust/sand whirls (PO), blowing dust (BLDU), blowing sand (BLSA), blowing snow (BLSN), sandstorm (SS), and duststorm (DS). Intensity qualifiers are not coded in conjunction with VC.
For example, VCFG can be decoded as meaning some form of fog is between 5 and 10 statute miles of the point of observation. If VCSH is coded, showers are occurring between 5 and 10 statute miles of the point of observation.
Weather phenomena occurring at the point of observation (at the station) or in the vicinity of the point of observation are coded in the body of the report. Weather phenomena observed beyond 10SM from the point of observation (at the station) is not coded in the body but may be coded in the remarks section (Section 3.1.3.12).
3.1.3.8.3 Descriptor Qualifier Descriptors are qualifiers which further amplify weather phenomena and are used in conjunction with some types of precipitation and obscurations. The descriptor qualifiers are: shallow (MI), partial (PR), patches (BC), low drifting (DR), blowing (BL), shower(s) (SH), thunderstorm (TS), and freezing (FZ).
Only one descriptor is coded for each weather phenomena group, e.g., FZDZ.
The descriptors shallow (MI), partial (PR), and patches (BC) are only coded with FG, e.g., MIFG. Mist (BR) is not coded with any descriptor.
The descriptors low drifting (DR) and blowing (BL) will only be coded with dust (DU), sand (SA), and snow (SN), e.g., BLSN or DRSN. DR is coded with DU, SA, or SN for raised particles drifting less than six feet above the ground.
When blowing snow is observed with snow falling from clouds, both phenomena are reported,
e.g., SN BLSN. If blowing snow is occurring and the observer cannot determine whether or not snow is also falling, then BLSN is reported. Spray (PY) is coded only with blowing (BL).
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) The descriptor for showery-type precipitation (SH) is coded only with one or more of the precipitation qualifiers for rain (RA), snow (SN), ice pellets (PL), small hail (GS), or large hail (GR). The SH descriptor indicates showery-type precipitation. When any type of precipitation is coded with VC, the intensity and type of precipitation is not coded.
The descriptor for thunderstorm (TS) may be coded by itself when the thunderstorm is without associated precipitation. A thunderstorm may also be coded with the precipitation types of rain (RA), snow (SN), ice pellets (PL), small hail and/or snow pellets (GS), or hail (GR). For example, a thunderstorm with snow and small hail and/or snow pellets would be coded as TSSNGS. TS are not coded with SH.
The descriptor freezing (FZ) is only coded in combination with fog (FG), drizzle (DZ), or rain (RA), e.g., FZRA. FZ is not coded with SH.
3.1.3.8.4 Precipitation Precipitation is any of the forms of water particles, whether liquid or solid, that falls from the atmosphere and reaches the ground. The precipitation types are: drizzle (DZ), rain (RA), snow (SN), snow grains (SG), ice crystals (IC), ice pellets (IP), hail (GR), small hail and/or snow pellets (GS), and unknown precipitation (UP). UP is reported if an automated station detects the occurrence of precipitation but the precipitation sensor cannot recognize the type.
Up to three types of precipitation may be coded in a single present weather group. They are coded in order of decreasing dominance based on intensity.
3.1.3.8.5 Obscuration Obscurations are any phenomenon in the atmosphere, other than precipitation, reducing the horizontal visibility. The obscuration types are: mist (BR), fog (FG), smoke (FU), volcanic ash (VC), widespread dust (DU), sand (SA), haze (HZ), and spray (PY). Spray (PY) is coded only as BLPY.
With the exception of volcanic ash, low drifting dust, low drifting sand, low drifting snow, shallow fog, partial fog, and patches (of) fog, an obscuration is coded in the body of the report if the surface visibility is less than 7 miles or considered operationally significant. Volcanic ash is always reported when observed.
3.1.3.8.6 Other Weather Phenomena Other weather phenomena types include: well-developed dust/sand whirls (PO), sand storms (SS), dust storms (DS), squalls (SQ), funnel clouds (FC), and tornados and waterspouts (+FC).
Examples:
-DZ L i g h t drizzle -RASN Light rain and snow SN BR (Moderate) snow, mist
-FZRA FG Light freezing rain, fog SHRA (Moderate) rain shower VCBLSA Blowing sand in the vicinity -RASN FG HZ Light rain and snow, fog, haze TS Thunderstorm (without precipitation) AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-11
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) +TSRA Thunderstorm, heavy rain +FC TSRAGR BR Tornado, thunderstorm, (moderate) rain, hail, mist
3.1.3.9 Sky Condition 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
Sky condition is a description of the appearance of the sky. It is coded as: sky condition, vertical visibility, or clear skies.
The sky condition group is based on the amount of sky cover (the first three letters) followed by the height of the base of the sky cover (final three digits). No space is between the amount of sky cover and the height of the layer. The height of the layer is recorded in feet Above Ground Level (AGL).
Sky condition is coded in ascending order and ends at the first overcast layer. At mountain stations, if the layer is below station level, the height of the layer will be coded as ///.
Vertical visibility is coded as VV followed by the vertical visibility into the indefinite ceiling. No space is between the group identifier and the vertical visibility. Figure 3-3 illustrates the effect of an obscuration on the vision from a descending aircraft.
Figure 3-3. Obscuration Effects on Slant Range Visibility The ceiling is 500 feet in both examples, but the indefinite ceiling example (bottom) produces a more adverse impact to landing aircraft. This is because an obscuration (e.g., fog, blowing dust, snow, etc.) limits runway AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-12
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) acquisition due to reduced slant range visibility. This pilot would be able to see the ground but not the runway. If the pilot was at approach minimums, the approach could not be continued and a missed approach must be executed.
Clear skies are coded in the format, SKC or CLR. When SKC is used, an observer indicates no layers are present; and CLR is used by automated stations to indicate no layers are detected at or below 12,000 feet.
Each coded layer is separated from the others by a space. Each layer reported is coded by using the appropriate reportable contraction seen in Table 3-3. A report of clear skies (SKC or CLR) is a complete layer report within itself. The abbreviations FEW, SCT, BKN, and OVC will be followed, without a space, by the height of the layer.
Table 3-3. METAR/SPECI Contractions for Sky Cover Reportable Contraction Meaning Summation Amount of Layer VV Vertical Visibility 8/8 SKC or CLR1 Clear 0 FEW2 Few 1/8 – 2/8 SCT Scattered 3/8 – 4/8 BKN Broken 5/8 – 7/8 OVC Overcast 8/8
1. The abbreviation CLR will be used at automated stations when no layers at or below 12,000 feet are reported; the abbreviation SKC will be used at manual stations when no layers are reported.
2. Any layer amount less than 1/8 is reported as FEW.
The height is coded in hundreds of feet above the surface using three digits in accordance with Table 3-4.
Table 3-4. METAR/SPECI Increments of Reportable Values of Sky Cover Height Range of Height Values (feet) Reportable Increment (feet) Less than or equal to 5,000 To nearest 100 5,001 to 10,000 To nearest 500 Greater than 10,000 To nearest 1,000
The ceiling is the lowest layer aloft reported as broken or overcast. If the sky is totally obscured with ground based clouds, the vertical visibility is the ceiling.
AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-13
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 3-4. METAR/SPECI Sky Condition Coding Clouds at 1,200 feet obscure 2/8ths of the sky (FEW). Higher clouds at 3,000 feet obscure an additional 1/8th of the sky, and because the observer cannot see above the 1,200-foot layer, he is to assume that the higher 3,000-foot layer also exists above the lower layer (SCT). The highest clouds at 5,000 feet obscure 2/8ths of the sky, and again since the observer cannot see past the 1,200 and 3,000-foot layers, he is to assume the higher 5,000-foot layer also exists above the lower layers (BKN). The sky condition group would be coded as: FEW012 SCT030 BKN050.
At manual stations, cumulonimbus (CB) or towering cumulus (TCU) is appended to the associated layer. For example, a scattered layer of towering cumulus at 1,500 feet would be coded SCT015TCU and would be followed by a space if there were additional higher layers to code.
Examples:
SKC No layers are present CLR No layers are detected at or below 12,000 feet AGL FEW004 Few at 400 feet AGL SCT023TCU Scattered layer of towering cumulus at 2,300 feet BKN105 Broken layer ( ceiling) at 10,500 feet OVC250 Overcast layer ( ceiling) at 25,000 feet VV001 Indefinite ceiling with a vertical visibility of 100 feet FEW012 SCT046 Few clouds at 1,200 feet, scattered layer at 4,600 feet SCT033 BKN085 Scattered layer at 3,300 feet, broken layer ( ceiling) at 8,500 feet SCT018 OVC032CB Scattered layer at 1,800 feet, overcast layer ( ceiling) of cumulonimbus at 7,500 feet SCT009 SCT024 BKN048 Scattered layer at 900 feet, scattered layer at 2,400 feet, broken layer (ceiling) at 4,800 feet
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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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