Terminal Aerodrome Forecast

Terminal Aerodrome Forecast

Introduction:

  • Terminal Aerodrome Forecasts (TAFs) are concise statements of the expected meteorological conditions within a 5 SM radius from the center of an airport’s runway complex
  • TAFs can be found on the National Oceanic and Atmospheric Administration’s website athttp://www.aviationweather.gov/adds/tafs or through use of the java tool here
    • Can be retrieved in the raw coded format or a translated format as shown in the picture below
  • TAFs and Routine Aviation Weather Reports (METARs) are very similar but deviate wind shear, temperature, icing, and turbulence groups being added to the TAF, when applicable
  • 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

 

Figure 1: AviationWeather.gov Raw or Translated TAF Query
AviationWeather.gov Raw or Translated TAF Query

Issuance & Validity:

  • 4 times daily (0000Z, 06000Z, 1200Z, 1800Z)
  • Valid for 24 hours
  • Data is forecasted

GROUP 1: Message Heading:

  • Begins with the four-letter ICAO location identifier
  • Next comes TAF and any modifiers
  • AMD for AMenDed

GROUP 2: Forecast Times:

  • Laid out in the DTG group (dd/hh/mm)
  • Two-digit date with a four-digit time group appended with Z to denote the time (UTC)
    • Example: 091730Z
      • TAF posted on the 9th day of the month at 1730 Zulu
  • Valid times may not be for 24 hours if previously amended, corrected, or delayed
  • Military TAFs will report the forecast period prior to the date and time
  • USN/USMC will append a remark as appropriate as well
    • Example: AMD2218
      • The TAF was amended at 2218Z

GROUP 3: Wind:

    • Direction in tens of degrees from true north (first 3 digits)
    • Velocity in whole knots (next 2 digits)
    • Six-digits if wind speed is 3 digits
    • Gusts included at the end with the letter G
    • Wind speed for the most recent 10 minutes is used to determine gusts and maximum peak is reported using two or three digits
    • Velocity appended with KT to indicate knots
    • Other countries may use KM / MPH / MPS
    • 00000KT for calm
    • If wind varies by 60° or more and speed greater than 6 knots, a variable wind direction is reported as a remark
    • If wind direction is variable and speed 6 knots or less, replace wind direction with VRB, followed by wind speed in knots; or in more rare cases when it is impossible to forecast a single wind direction such as thunderstorms
  • Example: 27010KT
    • Wind from 270 at 10 knots
  • Example: WND 270V350
    • Wind variable 270 to 350
  • Example: 14020KTG30
    • Wind from 140 at 20 knots, gusting to 30 knots
Figure 2: Weather Descriptors
Weather Descriptors

GROUP 4: Visibility, Weather, and Obstructions to Vision:

Meters SM
1,600 1
3,200 2
4,800 3
6,400 4
8,000 5
9,600 6
11,200 7
12,800 8
14,400 9
16,000 10
  • Civilian: forecasted prevailing visibility is reported in statute miles (SM)
  • Military: Forecasted prevailing visibility is reported in meters and rounded down to the nearest reportable value
  • Whenever the prevailing visibility is forecasted to be 9,000 meters or less (6 miles or less), the weather or obstructions to vision causing the reduced visibility will be included using the same notation as the METAR
  • 9999 indicates 7 miles visibility or greater is forecasted (unlimited visibility)
  • When appropriate, RVRs will follow immediately after the prevailing visibility
  • If any significant weather or obstruction to vision is forecasted it will be included after visibility using standard codes
  • Omitted if no weather is present

GROUP 5: Sky Condition Group:

  • Gives a description of the appearance of the sky, including cloud types/layers and sky coverage
  • Layers will be reported in ascending order up to the first overcast
  • Remember: a ceiling is defined as the first layer of broken or overcast
  • Clouds are reported by their base
  • All sky cover heights are reported in hundreds of feet above the ground level (AGL)
  • Reported in a 6-character group
  • For obscured sky:
    • VV = vertical visibility
    • VV is in hundreds of feet as well
    • More than 1 layer may be reported
  • Clouds may be followed by another modifier:
    • T = towering
    • CU = cumulus
    • CB = cumulonimbus
  • Example: SCT 030
    • For 3,000′ AGL scattered
  • Example: OVC 001
    • For 100′ AGL overcast
  • Example: VV008
    • For sky obscured, vertical visibility is 800′ AGL
Figure 2: Aviation Services Sky Cover Contractions
Aviation Services Sky Cover Contractions

GROUP 6: Special Wind Shear:

  • The three digits before the slash indicate the altitude (AGL)
  • The characters followed the slash indicate wind direction and speed
  • Some stations will insert this group immediately after the cloud group when it is forecasted for altitude 2000′ AGL and below
  • If wind cannot be forecast with accuracy, WSCONDS will be used with no numeric data
  • Group is omitted when no wind shear to be reported
    • Example: WS020/22030KT
      • Wind shear at 2000′ with wind from 220 at 30 knots
    • Example: WSOCNDS
      • Wind shear present

GROUP 7: Icing:

  • Consists of a six number group beginning with a 6
  • Forecasts non-thunderstorm icing
  • Omitted for no icing and repeated for multiple layers
  • 6 indicates that icing is forecasted
  • The next digit indicates the type of icing
  • The next three digits indicate the height of the base of the icing stratum in thousands of feet AGL
  • If the layer is thicker than 9,000′, the icing group is repeated so that the base of the repeated group coincides with the top of the first
    • Example: 640003
      • Moderate icing at or below 100′ AGL in a 3000′ layer

IC Type of Icing B Type of Turbulence
Code Description Code Description
0 No icing 0 Light turbulence
1 Light icing 1 Light turbulence
2 Light icing in cloud 2 Moderate turbulence in clear air, occasional
3 Light icing in precipitation 3 Moderate turbulence in clear air, frequent
4 Moderate icing 4 Moderate turbulence in cloud, occasional
5 Moderate icing in cloud 5 Moderate turbulence in cloud, frequent
6 Moderate icing in precipitation 6 Severe turbulence in clear air, occasional
7 Severe icing 7 Severe turbulence in clear air, frequent
8 Severe icing in cloud 8 Severe turbulence in cloud, occasional
9 Severe icing in precipitation 9 Severe turbulence in cloud, frequent
X Extreme turbulence

GROUP 8: Turbulence:

  • Similar to the icing group
  • Consists of six characters following the same format, however, beginning with a 5
  • Turbulence group forecasts non-thunderstorm turbulence
  • It is implied thunderstorms will be turbulent
    • Example: 510302
      • Light turbulence from 3000′ AGL in a 2000′ layer

GROUP 9: Altimeter:

  • Forecasts the lowest expected altimeter setting in inches of Hg
  • Forecasted during the initial forecast and each subsequent BECMG and FM group
  • TEMPO groups do not forecast the altimeter
  • This group is useful for lost comm. in IMC
  • QNH indicates sea level pressure is being given
  • INS indicates inches
  • QNE is the standard datum plane, 29.92 in-Hg
  • QFE is the actual station pressure not corrected to sea level
  • International stations report in millibars (a.k.a. hectopascals, hPa)
  • Q indicates millibars
    • Example: QNH2981INS
      • 29.81 in-Hg
    • Example: Q1013
      • 1013 millibars

GROUP 10: Remarks:

  • Noted with an RMK
  • Includes clarifying or augmented data
  • VC is used to indicate any condition within the forecasted area, 5 to 10 SM
  • A temperature group may be forecasted to facilitate VSTOL aircraft
  • Uses the same format as a METAR temperature remark

Change Group Terminology:

    • A new line of forecasted text is started for each change group
    • More than one change group may be reported
    • From (FM) indicates a quick change
    • Becoming (BECMG) indicates a change over time
    • Temporary (TEMPO) indicates a temporary or non-permanent change to the overall weather pattern, usually no longer than 3 hours
    • The TAF is valid from the time mentioned up to, but not including, the “to” time
    • FM Group:
      • The heading FM is followed by a time (hours and minutes) indicating the forecast time
      • All previously forecasted conditions are superseded by the conditions forecasted on this line
      • FM includes all normal forecasted items as required
        • Example: FM1200
          • From 1200Z to end at 00Z
      Figure 3: Airport Facility Directory (A/FD) TAF Decoder
      Airport Facility Directory (A/FD) TAF Decoder
    • BECMG Group:
      • A four-digit time code will be used, the first two indicate the beginning hour and the next two indicate the ending hour
      • The duration of this change is normally about 2 hours, 4 at the most
      • A group not edited from a previous line will be the same
        • Example: BECMG 1718
          • From 1700Z to 1800Z
    • TEMPO Group:
      • Followed by a four-digit time group to indicate conditions that will occur briefly and will not represent a permanent change to the overall forecast weather pattern
      • Tempo is used when the condition will be in the area less than half of the time
        • Example: TEMPO 1902
          • Temporarily between 1900 up to, but not including, 0200Z
  • PROB Group:
    • Probability of occurrence of thunderstorms or other events
    • Begins with PROB and a two-digit percentage
      • Example: PROB30 TS
        • 30% probability of thunderstorms

References: