Air Force TAF Code: AFMAN15-124

AFMAN15-124: Air Force Terminal Aerodrome Forecast (TAF) Code

• This manual outlines procedures for all AF Weather organizations/contractors involved in weather and solar forecasting for AF, Army, and DoD operations
• Compliance ensures aviation safety via international policy
• The chapter gives direction for encoding Terminal Aerodrome Forecasts (TAFs)
• Air Force weather organizations handle TAF specification, amendments, and dissemination, following AFI 15-128 guidelines

Code Formation

• Air Force weather forecast coding uses international standards from the World Meteorological Organization (WMO)
• The standards can be found in WMO No. 306, Manual on Codes, Volume I.1, Part A, Section FM 51, Aerodrome Forecast
• Practices align with Aviation Routine Weather Report (METAR) code
• METAR code can be found in AFMAN 15-111, Surface Weather Observations

Forecast Area Specifics

• Unless stated otherwise, forecast elements (clouds, weather, wind, etc.) cover an area within a 5 statute mile radius of the aerodrome center
• Weather beyond the 5-mile radius, extending to 10 statute miles, is encoded as VC (in the vicinity)
• The "vicinity" should be the limit for specifying elements in forecasts
• Forecast elements represent expected conditions during the forecast period and within the forecast area

TAF Encoding and Code Format

• Figure 1.1 displays the TAF Code Format
• MESSAGE HEADING is as follows: TAF (AMD or COR) CCCC YYGGggZ YYG1G1/YYG2G2 dddffGfmfmKT VVVV w’w’ NsNsNshshshsCC or VVhshshs or SKC (VAbbbttt) (WShxhxhx/dddfffKT) (6IchihihitL) (5BhBhBhBtL) QNHP1P1P1P1INS (Remarks) TTTTT YYGGGeGe or YYGG/YYGeGe ddffGfmfmKT…same as above… (Remarks) TX(M)TFTF/YYGFGFZ TN(M)TFTF/YYGFGFZ
• All TAFs are valid for a 30-hour forecast period
• Groups in parentheses are only used when the condition exists or is required

Symbolic Letters

• Message Heading includes the following: TAF [AMD or COR] CCCC YYGGggZ YYG1G1/YYG2G2
• The message heading contains a message identifier of TAF
• A forecast modifier indicates an amendment or correction (AMD or COR)
• Only one modifier can be used at a time
• For an amendment (AMD), the remaining valid forecast groups after the amendment time are included
• Groups no longer valid are removed
• For a correction (COR), the entire original text of the TAF, with the TAF header and any incorrect elements changed are issued
• Four Letter Location is identified by CCCC
• Issue Date and Time (YYGGggZ) includes the current date (YY), Coordinated Universal Time (UTC) in hours (GG) and minutes (gg), plus the letter Z
• This is updated with each change to a TAF
• Valid Period (YYG1G1/YYG2G2) notes the current date (YY) with a 30-hour forecast period, showing beginning (G1G1) and ending time (G2G2) in whole hours (except amended TAFs)
• All times are in UTC
• Midnight UTC is shown as 00 and 24
• Amended TAFs are valid from the current hour to when the original TAF ends

Change groups (TTTTT)

• One can use BECMG YYGG/YYGeGe, TEMPO YYGG/YYGeGe, and FM YYGGgg
• These indicate changes from predominant conditions at an intermediate date and hour (YYGGgg), or during a period between hours (YYGG to YYGeGe)
• TEMPO groups can forecast a change in any/all forecast groups and include a description of all elements in which a change is predicted
• EXCEPTION: Non-convective low-level wind shear and QNH groups are not included
• FM change groups must include all encoded elements, and forecasts will start on a new line
• Midnight UTC is indicated as 00 and 24 respectively
• Limit the number of change groups to those significant to airfield operations to avoid confusion
• Avoid overlapping forecast periods in order to keep the intent of the forecast simple

Becoming Change Indicator

• TTTTT YYGG/YYGeGe in BECMG YYGG/YYGeGe indicates a change to forecast prevailing conditions expected to occur at either a regular or irregular rate at an unspecified time within the period
• This is defined by a two-digit date (YY), two-digit change beginning time (GG) with a slash separating a two-digit date (YY), and a two-digit ending time (GeGe) in whole hours
• The time-period described by a BECMG group is usually for one hour, but never exceeds two hours
• Changes to predominant conditions are succeeded by a description of all elements for which the change is forecast
• Forecast conditions encoded after the BECMG YYGG/YYGeGe group are those elements expected to prevail from the ending time of this change group (GeGe) to the ending time of the forecast period (YYG2G2)
• Forecasted conditions must occur less than 30 minutes after the YYGeGe group start time
• When a BECMG group is employed to a change in one or more elements, repeat the entire element(s).
• EX: If the BECMG group was used to forecast a decrease in the ceiling and all other forecast layers were expected to remain the same, the entire cloud code group is repeated

Temporary Change Indicator

• TTTTT YYGG/YYGeGe in the form of TEMPO YYGG/YYGeGe group is used to indicate temporary fluctuations to the forecast meteorological conditions
• Conditions described by the TEMPO group must occur once during the specified time-period indicated by the date YY and time GG to the date YY and time GeGe, for less than 30 consecutive minutes
• Can also occur for an aggregate total of less than 30 minutes of every cardinal hour and cover less than half of the period indicated by the date YY and time GG to the date YY and time GeGe
• EXCEPTION: Organizations will allow 45 minutes for thunderstorms
• The extra 15 minutes provide for the 15-minute period between the time thunder is last heard and the time the thunderstorm is officially ended
• If forecast conditions in the TEMPO group last more than 30 consecutive minutes or are expected to last more than half of the period indicated by the time YYGG to YYGeGe, then it will be considered predominant
• It should be entered in the initial forecast period or following a FMYYGGgg or BECMG group

From Time Indicator

• YYGGgg in the form of FMYYGGgg indicates the beginning of a self-contained part of the forecast indicated by the two-digit date YY and four-digit time GGgg
• When FMYYGGgg is used, all forecast conditions preceding this group are superseded by the conditions forecasted in this group
• Ex: If the TAF period is 1909/2015 and a change is forecast at 1420 UTC, the entry FM191420 should be encoded
• Elements entered on this line are in effect from 191420 UTC to the end of the forecast period, 201500 UTC
• While a four-digit time in whole hours (e.g., 1600) remains acceptable, forecasts or amendments may require a higher time resolution, so use forecast minutes in that case
• Four-digit resolution will only be used in this FMGGgg group, and the forecasted conditions must occur in less than 30 minutes from the time specified in the YYGGgg group

Wind Group

• It is represented by (dddffGfmfmKT)
• Forecast true wind direction from which wind blows is represented by "(ddd)"
• It is measured to the nearest 10 degrees
• If direction varies more than 60 degrees, encode the prevailing direction for ddd and append the limits of variability to remarks (e.g., WND 270V350).
• Encode VRB for ddd if forecasting a prevailing direction is not possible
• encode dddff as 00000KT when winds are calm
• When wind speed is 6 knots or less and direction cant be determined, encode dddff as VRBff

Wind Speed and Gusts

• When wind speeds are be more than 6 knots, do not use VRB for ddd unless the situation involves air-mass thunderstorm activity during which forecasting a prevailing wind direction is not possible

• Encode wind group as VRBffGfmfmKT and append probable peak gust direction to remarks (e.g., GST DRCTN 250) when possible to forecast the peak gust direction, but not the prevailing direction

• Wind Speed (ff) is a mean forecast wind speed in whole knots and use three digits when speed is equal to or greater than 100 knots

• Gusts (Gfmfm) forecast speed or gusts in whole knots.

• Encode gusts when the maximum speed exceeds a mean speed (ff) by 10 knots or more or when the peak wind speed is forecast to exceed the lull by 10 knots or more.

• Encode gusts of 100 knots or more in three digits

• KT is the unit indicator for wind speeds in knots

Visibility Group

• Represented by (VVVV), which forecasts prevailing visibility in meters, rounded down to the nearest reportable value from Table 1.1
• Include weather and/or obscuration whenever visibility is forecast less than 9,999 meters
• If visibility alternates frequently from one significant value to another, describe the situation with a TEMPO group instead of using variable visibility remarks

Weather/Obscuration Reporting

• Weather, like precipitation, does not require a restriction to visibility to be reported
• This weather is significant because it is occurring, not restricting visibility
• AFMAN 15-111 defines weather and obscurations for construction of w’w’ groups (Table 1.2)
• Construct predominant forecast weather (w’w’) groups by considering Table 1.2, columns one to five in sequence
• This includes intensity/proximity, followed by description, followed by precipitation type, obscuration, or other weather phenomena
• One w’w’ group is normally included, and the group should be limited to three if more than one weather or obscuration condition exists
• Select/encode the three w’w’ that are most significant to operations when more than three w’w’ groups apply to a situation
• Funnel clouds (FC) and tornadoes (+FC) take precedence over all other w’w’ groups and are forecast as at the station and not in the vicinity

Weather Combinations

• VC may be encoded in combination with thunderstorms (TS), showers (SH), fog (FG), blowing snow (BLSN), blowing dust (BLDU), blowing sand (BLSA), well-developed dust/sand whirls (PO), sand storm (SS), and dust storm (DS)
• Place VC before the precipitation, obscuration, or other weather phenomena entry without a space between the two
• Do not encode intensity qualifiers with VC, and forecast weather in the vicinity is the last entry in the weather (w’w’) group
• Change group w’w’ is encoded as NSW (no significant weather) when an encoded predominant forecast condition is followed by a change group (BECMG or FM) without a w’w’ group
• NSW indicates that significant weather is no longer expected, including weather forecast in the vicinity
• Forecast Volcanic Ash (VA) as present weather regardless of restrictions to visibility when VA is observed or the Volcanic Ash Advisory Center (VAAC) forecast includes a surfaced-based VA plume

Squalls

• Forecast Squall (SQ) when wind rapidly increases at least 16 knots and is sustained at 22+ knots for one minute or longer

Clouds and Obscurations

• Report this group (NsNsNshshshsCC) as necessary for all conditions up to the first overcast layer
• Arrange groups in ascending order of cloud bases AGL
• Cloud Amount (NsNsNs) options:
  • SKC (sky clear = no clouds)
  • FEW (trace to 2/8ths)
  • SCT (3/8ths to 4/8ths)
  • BKN (5/8ths to 7/8ths)
  • OVC (8/8ths)
• Follow three-letter abbreviations with the height of the base of the cloud layer (mass) hshshs without a space
• The summation principle is defined by combining sky cover of the lowest layer, with all successively higher layers, up to and including, the layer being considered
• Do not assign sky cover to a layer less than a lower layer
• Encode VVhshshs when the sky is totally obscured
  • VV is the indicator and hshshs is the vertical visibility in hundreds of feet
• Ceiling Height (hshshs) is the height of the lowest broken or overcast layer above the earth
• Also includes vertical visibility into an indefinite ceiling, and all layers and obscuring phenomena should be opaque

Indefinite Ceilings

• (VVhshshs) The vertical visibility measured in feet, into a surface-based total obscuration, which hides the entire celestial dome (8/8ths)

Surface-Based Partial Obscuration

• Encode as FEW000, SCT000, or BKN000 as appropriate to indicate a surface-based partial obscuration
• Code as a remark the obscuring phenomena and the applicable layer (e.g., FG SCT000 fog obscures and layer amount is SCT)
• Include the amount of partial obscuration in your sky cover summation computation, but do not consider surface-based partial obscurations as a ceiling

Sky Conditions

• If two or more significant sky conditions alternate frequently, describe the situation with a TEMPO group instead of using variable sky condition remarks
• Cloud base is forecasted in hundreds of feet AGL, using ranges in Table 1.3
• Cloud Type (CC): Only the type Cumulonimbus (CB) is included; the contraction CB follows cloud or obscuration height (hshsh) without a space
• Cumulonimbus (CB) is included whenever thunderstorms are forecast, including those in the vicinity

Surface Wind Shear

• VA group describes volcanic ash
• Height of the base of the volcanic ash is encoded as "bbb" in hundreds of feet AGL
• Height of the top of the volcanic ash layer is encoded as "ttt" in hundreds of feet AGL, as forecast by the VAAC
• When forecasting VA to be surface based, encode VA as both present weather (w’w’) and add a VA group
• Non-Convective Low-Level Wind Shear Group forecasts wind shear not associated with convective activity from the surface up to and including 2,000 feet AGL
• Represented by (WShxhxhx/dddfffKT)
• The code for non-convective low-level wind shear is encoded as follows:
  • WS: low-level wind shear group indicator
  • hxhxhx: Forecast height of the wind shear in hundreds of feet AGL
  • ddd: Forecast wind direction, in tens of degrees true, above the indicated height- do not use VRB
  • ff: Forecast wind speed, in knots, of the forecast wind above the indicated height
  • KT: Unit indicator for wind speed in knots
• Non-convective low-level wind shear forecasts are included in the TAF, following the cloud forecast and before the altimeter setting forecast in the initial forecast period or in a FM or BECMG group
• Once included in the forecast, the wind shear group remains the prevailing condition until the next FM or BECMG group or until the end of the forecast valid period if there are no subsequent FM or BECMG groups
• Forecasts for non-convective low-level wind shear will not be included in TEMPO groups

Icing

• Icing Group is represented by (6IchihihitL), and is used to forecast icing not associated with thunderstorms
• For multiple layers, repeat as necessary, and omit when no icing is forecast
• Format with 6, the icing group indicator
• Ic: Type of icing use in Table 1.5
• When forecasting more than one type of icing within the same layer, encode the highest code figure
• hihihi: Height of base of forecasted icing layer in hundreds of feet AGL use in Table 1.4
• tL: icing layer thickness in thousands of feet use in Table 1.6
• Repeat the icing group with the base of the second group to coincide with the top layer given by the first group when the the coding dictates the layer to be thicker than 9,000 feet

Turbulence

• Turbulence group is represented by (5BhBhBhBtL), and it is used Forecast turbulence not associated with thunderstorms and applying to category II (CAT II) aircraft
• If forecasting none is required, then omit
• It can be formatted with: -5-turbulence group indicator -B-Type and intensity of turbulence use in Table 1.7 and encde the highest code figure, if forecasting more than on type -hBhBhB-Height of base of forecasted turbulence layer in hundreds of feet AGL use with Table 1.4 -tL-Thickness of the turbulence layer in thousands of feet use in Table 1.6
• Repeat the turbulence group with the base of the second group to coincide with the top layer given by the first group when the the coding dictates the layer to be thicker than 9,000 feet
• Icing and turbulence forecasts are for phenomena not associated with thunderstorm activity, from surface to 10,000 feet AGL
• Forecasters may address the areas above 10,000 feet mean sea level (MSL) provided the forecast in the TAF is horizontally consistent with turbulence products in the forecaster-in-the-loop (FITL) graphics

Altimeter, Temperature, and Remarks

• Lowest Altimeter group, represented by (QNHP1P1P1P1INS), sets an expected setting in inches of mercury during the initial forecast period
• It's the same process with each Becoming (BECMG) and From (FM) change group, however do not include QNH in Temporary (TEMPO) groups
• The altimeter is the same as: -QNH—Altimeter setting in inches of mercury indicator
  • P1P1P1P1—Forecast lowest altimeter setting
  • INS-Indicator for units of measure for inches of mercury
• TAF Remarks: Use alphabetic abbreviations in Table 1.2 and FAA Order JO 7340.2, Contractions is also allowed
• Operationally significant forecast elements should relate to geographical features
• Add start/end times without adding a Z when appliciable
• Check the start/end times and make sure they do not get confused with the numbers
• Do not uese terms like OCNL, VC or CB in remarks and don't use the remarks section as a substitute for a BECMG or TEMPO group
• encode the remarks in the following order
• Forecast Maximum and Minimum Temperature groups with T(X)(N)[M]TFTF/YYGFGFZ format and indicate a two-digit temperature (TFTF)
• To show maximum and minimum temperature expected, use the letter indicator TX for the maximum forecast temperature and TN for the minimum forecast temperature
• Should precede TFTF without a space or spaces
• The organization should encode forecast maximums (first entry) and minimum temperature (last entry) for the first 24 hours
  • TX— Maximum Temperature remark indicator
  • TN— Minimum Temperature remark indicator
• Precede temperatures between +9°C and -9°C with a zero (0) and temperatures below 0°C * by the letter M
• Use the following when a location has limited duty: indicate coordinate with their supporting Operational Weather Squadron on all TAF valid times
• YY is the day of the month UTC and GG is the time to the nearest whole hour
• Indicate when a airfield is closed with "LAST NO AMDS AFT YYGG NEXT YYGG"
  • airffild is closed and the TAF is no longer required as a coordinated requirement
• "LIMITED METWATCH YYGG TIL YYGG" should be used when operations have limited duty: when an airfield is open with no weather personnal or automated sensor running