7–1–29 International Civil Aviation Organization (ICAO) Weather Formats
The U.S. uses the ICAO world standard for aviation weather reporting and forecasting. The World Meteorological Organization’s (WMO) publication No. 782 “Aerodrome Reports and Forecasts” contains the base METAR and TAF code as adopted by the WMO member countries.
a. Although the METAR code is adopted worldwide, each country is allowed to make modifications or exceptions to the code for use in their particular country, e.g., the U.S. will continue to use statute miles for visibility, feet for RVR values, knots for wind speed, and inches of mercury for altimetry. However, temperature and dew point will be reported in degrees Celsius. The U.S. reports prevailing visibility rather than lowest sector visibility. The elements in the body of a METAR report are separated with a space. The only exceptions are RVR, temperature and dew point, which are separated with a solidus ( / ). When an element does not occur, or cannot be observed, the preceding space and that element are omitted from that particular report. A METAR report contains the following sequence of elements in the following order:
1. Type of report.
2. ICAO Station Identifier.
3. Date and time of report.
4. Modifier (as required).
5. Wind.
6. Visibility.
7. Runway Visual Range (RVR).
8. Weather phenomena.
9. Sky conditions.
10. Temperature/dew point group.
11. Altimeter.
12. Remarks (RMK).
b. The following paragraphs describe the elements in a METAR report.
1. Type of report. There are two types of report:
(a) Aviation Routine Weather Report (METAR); and
(b) Nonroutine (Special) Aviation Weather Report (SPECI).
The type of report (METAR or SPECI) will always appear as the lead element of the report.
2. ICAO Station Identifier. The METAR code uses ICAO 4-letter station identifiers. In the contiguous 48 States, the 3-letter domestic station identifier is prefixed with a “K;” i.e., the domestic identifier for Seattle is SEA while the ICAO identifier is KSEA. Elsewhere, the first two letters of the ICAO identifier indicate what region of the world and country (or state) the station is in. For Alaska, all station identifiers start with “PA;” for Hawaii, all station identifiers start with “PH.” Canadian station identifiers start with “CU,” “CW,” “CY,” and “CZ.” Mexican station identifiers start with “MM.” The identifier for the western Caribbean is “M” followed by the individual country’s letter; i.e., Cuba is “MU;” Dominican Republic “MD;” the Bahamas “MY.” The identifier for the eastern Caribbean is “T” followed by the individual country’s letter; i.e., Puerto Rico is “TJ.” For a complete worldwide listing see ICAO Document 7910, Location Indicators.
3. Date and Time of Report. The date and time the observation is taken are transmitted as a six-digit date/time group appended with Z to denote Coordinated Universal Time (UTC). The first two digits are the date followed with two digits for hour and two digits for minutes.
Example: 172345Z (the 17th day of the month at 2345Z)
4. Modifier (As Required). “AUTO” identifies a METAR/SPECI report as an automated weather report with no human intervention. If “AUTO” is shown in the body of the report, the type of sensor equipment used at the station will be encoded in the remarks section of the report. The absence of “AUTO” indicates that a report was made manually by an observer or that an automated report had human augmentation/backup. The modifier “COR” indicates a corrected report that is sent out to replace an earlier report with an error.
Note: There are two types of automated stations, AO1 for automated weather reporting stations without a precipitation discriminator, and AO2 for automated stations with a precipitation discriminator. (A precipitation discriminator can determine the difference between liquid and frozen/freezing precipitation). This information appears in the remarks section of an automated report.
5. Wind. The wind is reported as a five digit group (six digits if speed is over 99 knots). The first three digits are the direction the wind is blowing from, in tens of degrees referenced to true north, or “VRB” if the direction is variable. The next two digits is the wind speed in knots, or if over 99 knots, the next three digits. If the wind is gusty, it is reported as a “G” after the speed followed by the highest gust reported. The abbreviation “KT” is appended to denote the use of knots for wind speed.
Example:
13008KT—wind from 130 degrees at 8 knots
08032G45KT—wind from 080 degrees at 32 knots with gusts to 45 knots
VRB04KT—wind variable in direction at 4 knots
00000KT—wind calm
210103G130KT—wind from 210 degrees at 103 knots with gusts to 130 knots
If the wind direction is variable by 60 degrees or more and the speed is greater than 6 knots, a variable group consisting of the extremes of the wind direction separated by a “v” will follow the prevailing wind group.
32012G22KT 280V350
(a) Peak Wind. Whenever the peak wind exceeds 25 knots “PK WND” will be included in Remarks, e.g., PK WND 28045/1955 “Peak wind two eight zero at four five occurred at one niner five five.” If the hour can be inferred from the report time, only the minutes will be appended, e.g., PK WND 34050/38 “Peak wind three four zero at five zero occurred at three eight past the hour.”
(b) Wind shift. Whenever a wind shift occurs, “WSHFT” will be included in remarks followed by the time the wind shift began, e.g., WSHFT 30 FROPA “Wind shift at three zero due to frontal passage.”
6. Visibility. Prevailing visibility is reported in statute miles with “SM” appended to it.
Example:
7SM—seven statute miles
15SM—fifteen statute miles
1/2SM—one-half statute mile
(a) Tower/surface visibility. If either visibility (tower or surface) is below four statute miles, the lesser of the two will be reported in the body of the report; the greater will be reported in remarks.
(b) Automated visibility. ASOS/AWOS visibility stations will show visibility 10 or greater than 10 miles as “10SM.” AWOS visibility stations will show visibility less than 1/4 statute mile as “M1/4SM” and visibility 10 or greater than 10 miles as “10SM.”
Note: Automated sites that are augmented by human observer to meet service level requirements can report 0, 1/16 SM, and 1/8 SM visibility increments.
(c) Variable visibility. Variable visibility is shown in remarks (when rapid increase or decrease by 1/2 statute mile or more and the average prevailing visibility is less than three miles) e.g., VIS 1V2 “visibility variable between one and two.”
(d) Sector visibility. Sector visibility is shown in remarks when it differs from the prevailing visibility, and either the prevailing or sector visibility is less than three miles.
Example: VIS N2—visibility north two
7. Runway Visual Range (When Reported). “R” identifies the group followed by the runway heading (and parallel runway designator, if needed) “/” and the visual range in feet (meters in other countries) followed with “FT” (feet is not spoken).
(a) Variability Values. When RVR varies (by more than on reportable value), the lowest and highest values are shown with “V” between them.
(b) Maximum/Minimum Range. “P” indicates an observed RVR is above the maximum value for this system (spoken as “more than”). “M” indicates an observed RVR is below the minimum value which can be determined by the system (spoken as “less than”).
Example:
R32L/1200FT—runway three two left R-V-R one thousand two hundred.
R27R/M1000V4000FT—runway two seven right R-V-R variable from less than one thousand to four thousand.
8. Weather Phenomena. The weather as reported in the METAR code represents a significant change in the way weather is currently reported. In METAR, weather is reported in the format:
Intensity/Proximity/Descriptor/Precipitation/Obstruction to visibility/Other
Note: The “/ ” above and in the following descriptions (except as the separator between the temperature and dew point) are for separation purposes in this publication and do not appear in the actual METARs.
(a) Intensity applies only to the first type of precipitation reported. A “–” denotes light, no symbol denotes moderate, and a “+” denotes heavy.
(b) Proximity applies to and reported only for weather occurring in the vicinity of the airport (between 5 and 10 miles of the point(s) of observation). It is denoted by the letters “VC.” (Intensity and “VC” will not appear together in the weather group).
(c) Descriptor. These eight descriptors apply to the precipitation or obstructions to visibility:
TS: thunderstorm
DR: low drifting
SH: showers
MI: shallow
FZ: freezing
BC: patches
BL: blowing
PR: partial
Note: Although “TS” and “SH” are used with precipitation and may be preceded with an intensity symbol, the intensity still applies to the precipitation, not the descriptor.
(d) Precipitation. There are nine types of precipitation in the METAR code:
RA: rain
DZ: drizzle
SN: snow
GR: hail (1/4" or greater)
GS: small hail/snow pellets
PL: ice pellets
SG: snow grains
IC: ice crystals (diamond dust)
UP: unknown precipitation (automated stations only)
(e) Obstructions to visibility. There are eight types of obscuration phenomena in the METAR code (obscurations are any phenomena in the atmosphere, other than precipitation, that reduce horizontal visibility):
FG: fog (vsby less than 5/8 mile)
HZ: haze
FU: smoke
PY: spray
BR: mist (vsby 5/8–6 miles)
SA: sand
DU: dust
VA: volcanic ash
Note: Fog (FG) is observed or forecast only when the visibility is less than five-eighths of mile, otherwise mist (BR) is observed or forecast.
(f) Other. There are five categories of other weather phenomena which are reported when they occur:
SQ: squall
SS: sandstorm
DS: duststorm
PO: dust/sand whirls
FC: funnel cloud
+FC: tornado/waterspout
Examples:
TSRA: thunderstorm with moderate rain
+SN: heavy snow
-RA FG: light rain and fog
BRHZ: mist and haze (visibility 5⁄8 mile or greater)
FZDZ: freezing drizzle
VCSH: rain shower in the vicinity
+SHRASNPL: heavy rain showers, snow, ice pellets
(intensity indicator refers to the predominant rain)
9. Sky Condition. The sky condition as reported in METAR represents a significant change from the way sky condition is currently reported. In METAR, sky condition is reported in the format:
Amount/Height/(Type) or Indefinite Ceiling/Height
(a) Amount. The amount of sky cover is reported in eighths of sky cover, using the contractions:
SKC: clear (no clouds)
FEW: >0 to 2/8
SCT: scattered (3/8s to 4/8s of clouds)
BKN: broken (5/8s to 7/8s of clouds)
OVC: overcast (8/8s clouds)
CB: Cumulonimbus when present
TCU: Towering cumulus when present
Note 1: “SKC” will be reported at manual stations. “CLR” will be used at automated stations when no clouds below 12,000 feet are reported.
Note 2: A ceiling layer is not designated in the METAR code. For aviation purposes, the ceiling is the lowest broken or overcast layer, or vertical visibility into an obscuration. Also there is no provision for reporting thin layers in the METAR code. When clouds are thin, that layer must be reported as if it were opaque.
(b) Height. Cloud bases are reported with three digits in hundreds of feet above ground level (AGL). (Clouds above 12,000 feet cannot be reported by an automated station).
(c) (Type). If Towering Cumulus Clouds (TCU) or Cumulonimbus Clouds (CB) are present, they are reported after the height which represents their base.
Example:
(Reported as) SCT025TCU BKN080 BKN250 (spoken as) “TWO THOUSAND FIVE HUNDRED SCATTERED TOWERING CUMULUS, CEILING EIGHT THOUSAND BROKEN, TWO FIVE THOUSAND BROKEN.”
(Reported as) SCT008 OVC012CB (spoken as) “EIGHT HUNDRED SCATTERED CEILING ONE THOUSAND TWO HUNDRED OVERCAST CUMULONIMBUS CLOUDS.”
(d) Vertical Visibility (indefinite ceiling height). The height into an indefinite ceiling is preceded by “VV” and followed by three digits indicating the vertical visibility in hundreds of feet. This layer indicates total obscuration.
Example:
1/8SM FG VV006—visibility one eighth, fog, indefinite ceiling six hundred.
(e) Obscurations are reported when the sky is partially obscured by a ground-based phenomena by indicating the amount of obscuration as FEW, SCT, BKN followed by three zeros (000). In remarks, the obscuring phenomenon precedes the amount of obscuration and three zeros.
Example:
BKN000 (in body): “sky partially obscured”
FU BKN000 (in remarks): “smoke obscuring five- to seven-eighths of the sky”
(f) When sky conditions include a layer aloft, other than clouds, such as smoke or haze the type of phenomena, sky cover and height are shown in remarks.
Example:
BKN020 (in body): “ceiling two thousand broken”
RMK FU BKN020: “broken layer of smoke aloft, based at two thousand”
(g) Variable ceiling. When a ceiling is below three thousand and is variable, the remark “CIG” will be shown followed with the lowest and highest ceiling heights separated by a “V.”
Example:
CIG 005V010: “ceiling variable between five hundred and one thousand”
(h) Second site sensor. When an automated station uses meteorological discontinuity sensors, remarks will be shown to identify site specific sky conditions which differ and are lower than conditions reported in the body.
Example:
CIG 020 RY11: “ceiling two thousand at runway one one”
(i) Variable cloud layer. When a layer is varying in sky cover, remarks will show the variability range. If there is more than one cloud layer, the variable layer will be identified by including the layer height.
Example:
SCT V BKN: “scattered layer variable to broken”
BKN025 V OVC: “broken layer at two thousand five hundred variable to overcast”
(j) Significant clouds. When significant clouds are observed, they are shown in remarks, along with the specified information as shown below:
(1) Cumulonimbus (CB), or Cumulonimbus Mammatus (CBMAM), distance (if known), direction from the station, and direction of movement, if known. If the clouds are beyond 10 miles from the airport, DSNT will indicate distance.
Example:
CB W MOV E: “cumulonimbus west moving east”
CBMAM DSNT S: “cumulonimbus mammatus distant south”
(2) Towering Cumulus (TCU), location, (if known), or direction from the station.
Example:
TCU OHD: “towering cumulus overhead”
TCU W: “towering cumulus west”
(3) Altocumulus Castellanus (ACC), Stratocumulus Standing Lenticular (SCSL), Altocumulus Standing Lenticular (ACSL), Cirrocumulus Standing Lenticular (CCSL) or rotor clouds, describing the clouds (if needed) and the direction from the station.
Example:
ACC W: “altocumulus castellanus west”
ACSL SW-S: “standing lenticular altocumulus southwest through south”
APRNT ROTOR CLD S: “apparent rotor cloud south”
CCSL OVR MT E: “standing lenticular cirrocumulus over the mountains east”
10. Temperature/Dew Point. Temperature and dew point are reported in two, two-digit groups in degrees Celsius, separated by a solidus (“/”). Temperatures below zero are prefixed with an “M.” If the temperature is available but the dew point is missing, the temperature is shown followed by a solidus. If the temperature is missing, the group is omitted from the report.
Example:
15/08: “temperature one five, dew point 8”
00/M02: “temperature zero, dew point minus 2”
M05/: “temperature minus five, dew point missing”
11. Altimeter. Altimeter settings are reported in a four-digit format in inches of mercury prefixed with an “A” to denote the units of pressure.
Example:
A2995: “Altimeter two niner niner five”
12. Remarks. Remarks will be included in all observations, when appropriate. The contraction “RMK” denotes the start of the remarks section of a METAR report.
Except for precipitation, phenomena located within 5 statute miles of the point of observation will be reported as at the station. Phenomena between 5 and 10 statute miles will be reported in the vicinity, “VC.” Precipitation not occurring at the point of observation but within 10 statute miles is also reported as in the vicinity, “VC.” Phenomena beyond 10 statute miles will be shown as distant, “DSNT.” Distances are in statute miles except for automated lightning remarks which are in nautical miles. Movement of clouds or weather will be indicated by the direction toward which the phenomena is moving.
(a) There are two categories of remarks:
(1) Automated, manual, and plain language.
(2) Additive and automated maintenance data.
(b) Automated, Manual, and Plain Language.
This group of remarks may be generated from either manual or automated weather reporting stations and generally elaborate on parameters reported in the body of the report. (Plain language remarks are only provided by manual stations).
(1) Volcanic eruptions.
(2) Tornado, Funnel Cloud, Waterspout.
(3) Station Type (AO1 or AO2).
(4) PK WND.
(5) WSHFT (FROPA).
(6) TWR VIS or SFC VIS.
(7) VRB VIS.
(8) Sector VIS.
(9) VIS @ 2nd Site.
(10) Lightning. When lightning is observed at a manual location, the frequency and location is reported.
When cloud-to-ground lightning is detected by an automated lightning detection system, such as ALDARS:
[a] Within 5 nautical miles (NM) of the Airport Reference Point (ARP), it will be reported as “TS” in the body of the report with no remark;
[b] Between 5 and 10 NM of the ARP, it will be reported as “VCTS” in the body of the report with no remark;
[c] Beyond 10 but less than 30 NM of the ARP, it will be reported in remarks as “DSNT” followed by the direction from the ARP.
Example: LTG DSNT W or LTG DSNT ALQDS
(11) Beginning/Ending of Precipitation/TSTMS.
(12) TSTM Location MVMT.
(13) Hailstone Size (GR).
(14) Virga.
(15) VRB CIG (height).
(16) Obscuration.
(17) VRB Sky Condition.
(18) Significant Cloud Types.
(19) Ceiling Height 2nd Location.
(20) PRESFR PRESRR.
(21) Sea-Level Pressure.
(22) ACFT Mishap (not transmitted).
(23) NOSPECI.
(24) SNINCR.
(25) Other SIG Info.
(c) Additive and Automated Maintenance Data.
(1) Hourly Precipitation.
(2) 3- and 6-Hour Precipitation Amount.
(3) 24-Hour Precipitation.
(4) Snow Depth on Ground.
(5) Water Equivalent of Snow.
(6) Cloud Type.
(7) Duration of Sunshine.
(8) Hourly Temperature/Dew Point (Tenths).
(9) 6-Hour Maximum Temperature.
(10) 6-Hour Minimum Temperature.
(11) 24-Hour Maximum/Minimum Temperature.
(12) Pressure Tendency.
(13) Sensor Status.
PWINO
FZRANO
TSNO
RVRNO
PNO
VISNO
Examples of METAR reports and explanation:
METAR: aviation routine weather report
KBNA: Nashville, TN
281250Z: date 28th, time 1250 UTC
(no modifier): This is a manually generated report, due to the absence of “AUTO” and “AO1 or AO2” in remarks
33018KT: wind three three zero at one eight
290V360: wind variable between two nine zero and three six zero
1/2SM: visibility one half
R31/2700FT: Runway three one RVR two thousand seven hundred
SN: moderate snow
BLSN FG: visibility obscured by blowing snow and fog
VV008: indefinite ceiling eight hundred
00/M03: temperature zero, dew point minus three
A2991: altimeter two niner niner one
RMK: remarks
RAE42: rain ended at four two
SNB42: snow began at four two
METAR: aviation routine weather report
KSFO: San Francisco, CA
041453Z: date 4th, time 1453 UTC
AUTO: fully automated; no human intervention
VRB02KT: wind variable at two
3SM: visibility three
BR: visibility obscured by mist
CLR: no clouds below one two thousand
15/12: temperature one five, dew point one two
A3012: altimeter three zero one two
RMK: remarks
AO2: this automated station has a weather discriminator (for precipitation)
SPECI: (nonroutine) aviation special weather report
KCVG: Cincinnati, OH
152228Z: date 15th, time 2228 UTC
(no modifier): This is a manually generated report due to the absence of “AUTO” and “AO1 or AO2” in remarks
28024G36KT: wind two eight zero at two four gusts three six
3/4SM: visibility three fourths
+TSRA: thunderstorms, heavy rain
BKN008: ceiling eight hundred broken
OVC020CB: two thousand overcast cumulonimbus clouds
28/23: temperature two eight, dew point two three
A3000: altimeter three zero zero zero
RMK: remarks
TSRAB24: thunderstorm and rain began at two four
TS W MOV E: thunderstorm west moving east
c. Aerodrome Forecast (TAF). A concise statement of the expected meteorological conditions at an airport during a specified period. At most locations, TAFs have a 24 hour forecast period. However, TAFs for some locations have a 30 hour forecast period. These forecast periods may be shorter in the case of an amended TAF. TAFs use the same codes as METAR weather reports. They are scheduled four times daily for 24-hour periods beginning at 0000Z, 0600Z, 1200Z, and 1800Z.
Forecast times in the TAF are depicted in two ways. The first is a 6-digit number to indicate a specific point in time, consisting of a two-digit date, two-digit hour, and two-digit minute (such as issuance time or FM). The second is a pair of four-digit numbers separated by a “/” to indicate a beginning and end for a period of time. In this case, each four-digit pair consists of a two-digit date and a two-digit hour.
TAFs are issued in the following format:
Note: The “ / ” above and in the following descriptions are for separation purposes in this publication and do not appear in the actual TAFs.
TAF KORD 051130Z 0512/0618 14008KT 5SM BR BKN030
TEMPO 0513/0516 1 1/2SM BR
FM051600 16010KT P6SM SKC
FM052300 20013G20KT 4SM SHRA OVC020
PROB40 0600/0606 2SM TSRA OVC008CB
BECMG 0606/0608 21015KT P6SM NSW SCT040
TAF format observed in the above example:
TAF = type of report
KORD = ICAO station identifier
051130Z = date and time of origin (issuance time)
0512/0618 = valid period date and times
14008KT 5SM BR BKN030 = forecast meteorological conditions
Explanation of TAF elements
1. Type of Report. There are two types of TAF issuances, a routine forecast issuance (TAF) and an amended forecast (TAF AMD). An amended TAF is issued when the current TAF no longer adequately describes the on-going weather or the forecaster feels the TAF is not representative of the current or expected weather. Corrected (COR) or delayed (RTD) TAFs are identified only in the communications header which precedes the actual forecasts.
2. ICAO Station Identifier. The TAF code uses ICAO 4-letter location identifiers as described in the METAR section.
3. Date and Time of Origin. This element is the date and time the forecast is actually prepared. The format is a two-digit date and four-digit time followed, without a space, by the letter “Z.”
4. Valid Period Date and Time. The UTC valid period of the forecast consists of two four-digit sets, separated by a “/”. The first four-digit set is a two-digit date followed by the two-digit beginning hour, and the second four-digit set is a two-digit date followed by the two-digit ending hour. Although most airports have a 24-hour TAF, a select number of airports have a 30-hour TAF. In the case of an amended forecast, or a forecast which is corrected or delayed, the valid period may be for less than 24 hours. Where an airport or terminal operates on a part-time basis (less than 24 hours/day), the TAFs issued for those locations will have the abbreviated statement “AMD NOT SKED” added to the end of the forecasts. The time observations are scheduled to end and/or resume will be indicated by expanding the AMD NOT SKED statement. Expanded statements will include:
(a) Observation ending time (AFT DDHHmm; for example, AFT 120200)
(b) Scheduled observations resumption time (TIL DDHHmm; for example, TIL 171200Z) or
(c) Period of observation unavailability (DDHH/DDHH); for example, 2502/2512).
5. Forecast Meteorological Conditions. This is the body of the TAF. The basic format is:
The wind, visibility, and sky condition elements are always included in the initial time group of the forecast. Weather is included only if significant to aviation. If a significant, lasting change in any of the elements is expected during the valid period, a new time period with the changes is included. It should be noted that with the exception of a “FM” group the new time period will include only those elements which are expected to change, i.e., if a lowering of the visibility is expected but the wind is expected to remain the same, the new time period reflecting the lower visibility would not include a forecast wind. The forecast wind would remain the same as in the previous time period.
Any temporary conditions expected during a specific time period are included with that time period. The following describes the elements in the above format.
(a) Wind. This five (or six) digit group includes the expected wind direction (first 3 digits) and speed (last 2 digits or 3 digits if 100 knots or greater). The contraction “KT” follows to denote the units of wind speed. Wind gusts are noted by the letter “G” appended to the wind speed followed by the highest expected gust.
A variable wind direction is noted by “VRB” where the three digit direction usually appears. A calm wind (3 knots or less) is forecast as “00000KT.”
Example:
18010KT: wind one eight zero at one zero (wind is blowing from 180)
35012G20KT: wind three five zero at one two gust two zero
(b) Visibility. The expected prevailing visibility up to and including 6 miles is forecast in statute miles, including fractions of miles, followed by “SM” to note the units of measure. Expected visibilities greater than 6 miles are forecast as P6SM (plus six statute miles).
Example:
1/2SM—visibility one-half
4SM—visibility four
P6SM—visibility more than six
(c) Weather Phenomena. The expected weather phenomena is coded in TAF reports using the same format, qualifiers, and phenomena contractions as METAR reports (except UP).
Obscurations to vision will be forecast whenever the prevailing visibility is forecast to be 6 statute miles or less.
If no significant weather is expected to occur during a specific time period in the forecast, the weather phenomena group is omitted for that time period. If, after a time period in which significant weather phenomena has been forecast, a change to a forecast of no significant weather phenomena occurs, the contraction NSW (No Significant Weather) will appear as the weather group in the new time period. (NSW is included only in TEMPO groups).
Note: It is very important that pilots understand that NSW only refers to weather phenomena, i.e., rain, snow, drizzle, etc. Omitted conditions, such as sky conditions, visibility, winds, etc., are carried over from the previous time group.
(d) Sky Condition. TAF sky condition forecasts use the METAR format described in the METAR section. Cumulonimbus clouds (CB) are the only cloud type forecast in TAFs.
When clear skies are forecast, the contraction “SKC” will always be used. The contraction “CLR” is never used in the TAF.
When the sky is obscured due to a surface-based phenomenon, vertical visibility (VV) into the obscuration is forecast. The format for vertical visibility is “VV” followed by a three-digit height in hundreds of feet.
Note: As in METAR, ceiling layers are not designated in the TAF code. For aviation purposes, the ceiling is the lowest broken or overcast layer or vertical visibility into a complete obscuration.
SKC: “sky clear”
SCT005 BKN025CB: “five hundred scattered, ceiling two thousand five hundred broken cumulonimbus clouds”
VV008: “indefinite ceiling eight hundred”
(e) Optional Data (Wind Shear). Wind shear is the forecast of nonconvective low level winds (up to 2,000 feet). The forecast includes the letters “WS” followed by the height of the wind shear, the wind direction and wind speed at the indicated height and the ending letters “KT” (knots). Height is given in hundreds of feet (AGL) up to and including 2,000 feet. Wind shear is encoded with the contraction “WS,” followed by a three-digit height, slant character “/,” and winds at the height indicated in the same format as surface winds. The wind shear element is omitted if not expected to occur.
d. Probability Forecast. The probability or chance of thunderstorms or other precipitation events occurring, along with associated weather conditions (wind, visibility, and sky conditions). The PROB30 group is used when the occurrence of thunderstorms or precipitation is 30–39% and the PROB40 group is used when the occurrence of thunderstorms or precipitation is 40–49%. This is followed by two four-digit groups separated by a “/”, giving the beginning date and hour, and the ending date and hour of the time period during which the thunderstorms or precipitation are expected.
Note: NWS does not use PROB 40 in the TAF. However U.S. Military generated TAFS may include PROB40. PROB30 will not be shown during the first nine hours of a NWS forecast.
Example:
PROB40 2221/2302 1/2SM +TSRA: “chance between 2100Z and 0200Z of visibility one-half statute mile in thunderstorms and heavy rain.”
PROB30 3010/3014 1SM RASN: “chance between 1000Z and 1400Z of visibility one statute mile in mixed rain and snow.”
e. Forecast Change Indicators. The following change indicators are used when either a rapid, gradual, or temporary change is expected in some or all of the forecast meteorological conditions. Each change indicator marks a time group within the TAF report.
1. From (FM) group. The FM group is used when a rapid change, usually occurring in less than one hour, in prevailing conditions is expected. Typically, a rapid change of prevailing conditions to more or less a completely new set of prevailing conditions is associated with a synoptic feature passing through the terminal area (cold or warm frontal passage). Appended to the “FM” indicator is the six-digit date, hour, and minute the change is expected to begin and continues until the next change group or until the end of the current forecast. A “FM” group will mark the beginning of a new line in a TAF report (indented 5 spaces). Each “FM” group contains all the required elements—wind, visibility, weather, and sky condition. Weather will be omitted in “FM” groups when it is not significant to aviation. FM groups will not include the contraction NSW.
Example:
FM210100 14010KT P6SM SKC—“after 0100Z on the 21st, wind one four zero at one zero, visibility more than six, sky clear.”
2. Becoming (BECMG) group. The BECMG group is used when a gradual change in conditions is expected over a longer time period, usually two hours. The time period when the change is expected is two four-digit groups separated by a “/”, with the beginning date and hour, and ending date and hour of the change period which follows the BECMG indicator. The gradual change will occur at an unspecified time within this time period. Only the changing forecast meteorological conditions are included in BECMG groups. The omitted conditions are carried over from the previous time group.
Note: The NWS does not use BECMG in the TAF.
Example:
OVC012 BECMG 0114/0116 BKN020—“ceiling one thousand two hundred overcast. Then a gradual change to ceiling two thousand broken between 1400Z on the 1st and 1600Z on the 1st.”
3. Temporary (TEMPO) group. The TEMPO group is used for any conditions in wind, visibility, weather, or sky condition which are expected to last for generally less than an hour at a time (occasional), and are expected to occur during less than half the time period. The TEMPO indicator is followed by two four-digit groups separated by a “/”. The first four digit group gives the beginning date and hour, and the second four digit group gives the ending date and hour of the time period during which the temporary conditions are expected. Only the changing forecast meteorological conditions are included in TEMPO groups. The omitted conditions are carried over from the previous time group.
Example 1:
SCT030 TEMPO 0519/0523 BKN030—“three thousand scattered with occasional ceilings three thousand broken between 1900Z on the 5th and 2300Z on the 5th.”
Example 2:
4SM HZ TEMPO 1900/1906 2SM BR HZ—“visibility four in haze with occasional visibility two in mist and haze between 0000Z on the 19th and 0600Z on the 19th.”