Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-22
7.2.2 Generic Format of the Forecast Text of a NWS-Prepared TAF
TAF or
TAF AMD Type of report
CCCC YYGGggZ YlY1G1G1G2G2 DddffGfmfmKT Location identifier Date/time of forecast origin group Valid period Wind group
VVVV w'w' or NSW NsNsNshshshs or VVhshshs or SKC WShwshwshws/dddftKT Visibility group Significant weather group Cloud and vertical obscuration groups Non-convective low-level wind shear (LLWS) group
TTGGgg Forecast change indicator groups
FMGG GGGeGe TEMPO GGGeGe PROB40GGGeGe “From” group “Temporary” group Probability Forecast
7.2.2.1 Type of Report (TAF or TAF AMD) The report-type header always appears as the first element in the TAF and is produced in two forms: a routine forecast, TAF, and an amended forecast, TAF AMD.
TAFs are amended whenever they become, in the forecaster's judgment, unrepresentative of existing or expected conditions, particularly regarding those elements and events significant to aircraft and airports. An amended forecast is identified by TAF AMD (in place of TAF) on the first line of the forecast text.
7.2.2.2 Location Identifier (CCCC) After the line containing either TAF or TAF AMD, each TAF begins with its four-letter International Civil Aviation Organization (ICAO) location identifier. Figures 7-8, 7-9 and 7-10 contains the locations of NWS issued TAFs.
Examples:
KDFW – Dallas-Fort Worth PANC – Anchorage, Alaska PHNL – Honolulu, Hawaii
7.2.2.3 Date/Time of Forecast Origin Group (YYGGggZ) The date/time of forecast origin group (YYGGggZ) follows the terminal's location identifier. It contains the day of the month in two (2) digits (YY) and time in four (4) digits (GGgg in hours
Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-23 and minutes) the forecast is completed and ready for transmission, with a Z appended to denote UTC. This time is entered by the forecaster.
Examples 061737Z The TAF was issued on the 6th day of the month at 1737 UTC.
121123Z The TAF was issued on the 12th day of the month at 1123 UTC.
7.2.2.4 Valid Period (Y1Y1G1G1G2G2) The TAF valid period (Y1Y1G1G1G2G2) is the next group. Scheduled 24-hour TAFs are issued four (4) times per day, at 0000, 0600, 1200, and 1800Z. The first two digits (Y1Y1) are the day of the month for the start of the TAF. The next two digits (G1G1) are the starting hour, and the last two digits (G2G2) are the ending hour of the valid period. A forecast period beginning at midnight UTC is annotated as 00. If the end time of a valid period is at midnight UTC, it is annotated as 24. For example, a 00Z TAF issued on the 9th of the month would have a valid period of 090024.
Examples:
151212 The TAF is valid from 1200 UTC on the 15th of the month until 1200 UTC on the 16th.
230606 The TAF is valid from 0600 UTC on the 23rd of the month until 0600 UTC on the 24th of the month.
011818 The TAF is valid from 1800 UTC on the 1st of the month until 1800 UTC on the 2nd of the month.
060024 The TAF is valid from 0000 UTC on the 6th of the month until 0000 UTC on the 7th of the month.
7.2.2.5 Valid Period of Amended TAFs An amended TAF (TAF AMD) covers all of the remaining valid period of the original scheduled forecast. Expired portions of the amended forecast or references to weather occurring before the issuance time are omitted from the amendment.
In an amended forecast, the date and time of the forecast origin group (YYGGggZ) reflects the time the amended forecast was prepared. In the forecast valid period group (Y1Y1G1G1G2G2), the first four digits (Y1Y1G1G1) reflect the UTC date and time of the beginning of the valid period of the amended TAF.
With an issuance time (YYGGggZ) in the first half hour of any given hour (:00 to :29), the current hour (based on UTC) is used to denote the beginning valid time. For example, an amended TAF issued at 1416Z would be valid from 1400 UTC until the standard ending time of the TAF. For the second half of any given hour (:30 to :59), the next hour (based on UTC) is used for the beginning valid time. For example, an amended TAF issued at 1639Z would be valid from 1700 UTC until the standard ending time of the TAF.
Example:
Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-24
Original Amended
TAF TAF AMD PAEN 030540Z 030606... PAEN 031012Z 031006...
The scheduled forecast was sent, and 4 ½ hours later, the forecaster prepared an amendment to the forecast, at 1012Z on the 3rd day of the month.
7.2.2.6 Wind Group (dddffGfmfmKT) The initial time period and any subsequent FM (section 7.1.12.12.1) groups begin with a mean surface wind forecast (dddffGfmfmKT) for the period. Wind forecasts are expressed as the mean three-digit direction (ddd - relative to true north) rounded to the nearest ten degrees and the mean wind speed in knots (ff) for the time period. If wind gusts are forecast (gusts are defined as rapid fluctuations in wind speeds with a variation of 10 knots or more between peaks and lulls), they are indicated immediately after the mean wind speed by the letter G, followed by the peak gust speed expected. KT is appended to the end of the wind forecast group. Any wind speed of 100 knots or more will be encoded in three digits. Calm winds are encoded as 00000KT.
The prevailing wind direction is forecast for any speed greater than or equal to seven (7) knots.
When the prevailing surface wind direction is variable (variations in wind direction of 30 degrees or more), the forecast wind direction is encoded as VRBffKT. Two conditions where this can occur are very light winds and convective activity. Variable wind direction for very light winds must have a wind speed of one (1) through six (6) knots inclusive. For convective activity, the wind group may be encoded as VRBffGfmfmKT, where Gfmfm is the maximum expected wind gusts. VRB is not used in the non-convective LLWS group.
Squalls are forecast in the wind group as gusts (G), but must be identified in the significant weather group (Section 7.2.2.8) with the code SQ.
Examples:
23010KT Wind from 230 degrees “true” (southwest) at 10 knots.
28020G35KT Wind from 280 degrees “true” (west) at 20 knots gusting to 35 knots.
VRB05KT Wind variable at 5 knots. This example depicts a forecast for light winds that are expected to variable in direction.
VRB15G30KT Wind variable at 15 knots gusting to 30 knots. This example depicts winds that are forecast to be variable with convective activity.
00000KT Wind calm
090105KT Wind from 90 degrees at 105 knots
Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-25
7.2.2.7 Visibility Group (VVVV) The initial time period and any subsequent FM groups (section 7.1.12.12.1) include a visibility forecast (VVVV) in statute miles appended by the contraction SM.
When the prevailing visibility is forecast to be less than or equal to six (6) SM, one or more significant weather groups (Section 7.1.12.8) are included in the TAF. However, drifting dust (DRDU), drifting sand (DRSA), drifting snow (DRSN), shallow fog (MIFG), partial fog (PRFG), and patchy fog (BCFG) may be forecast with prevailing visibility greater than or equal to seven
(7) statute miles.
When a whole number and a fraction are used to forecast visibility, a space is included between them (e.g., 1 1/2SM). Visibility greater than six (6) statute miles is encoded as P6SM.
If the visibility is not expected to be the same in different directions, prevailing visibility is used.
When volcanic ash (VA) is forecast in the significant weather group, visibility is included in the forecast, even if it is unrestricted (P6SM). For example, an expected reduction of visibility to 10 statute miles by volcanic ash is encoded in the forecast as P6SM VA.
Examples
P6SM Visibility unrestricted
1 1/2SM Visibility 1 and ½ statute miles.
4SM Visibility 4 statute miles.
7.2.2.8 Significant Weather Group (w'w' or NSW) The significant weather group (w'w' or NSW) consists of the appropriate qualifier(s) and weather phenomenon contraction(s) (Section 2) or NSW (No significant weather).
If the initial forecast period and subsequent FM groups (Section 7.1.12.12.1) are not forecast to have explicit significant weather, the significant weather group is omitted. NSW is not used in the initial forecast time period or FM groups.
Tornadic activity (tornadoes, waterspouts, and funnel clouds) are not forecast in terminal forecasts because the probability of occurrence at a specific site is extremely small.
One or more significant weather group(s) is (are) required when the visibility is forecast to be 6SM or less. The exceptions are: volcanic ash (VA), low drifting dust (DRDU), low drifting sand (DRSA), low drifting snow (DRSN), shallow fog (MIFG), partial fog (PRFG), and patchy fog (BCFG). Obstructions to vision are only forecast when the prevailing visibility is less than 7 statute miles or, in the opinion of the forecaster, is considered operationally significant.
Volcanic ash (VA) is always forecast when expected. When VA is included in the significant weather group, visibility is included in the forecast as well, even if the visibility is unrestricted (P6SM).
Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-26 NSW is used in place of significant weather only in a TEMPO group (Section 7.1.12.12.2) to indicate when significant weather (including in the vicinity (VC), see below) included in a previous sub-divided group is expected to end.
Multiple precipitation elements are encoded in a single group (e.g., -TSRASN). If more than one type of precipitation is forecast, up to three appropriate precipitation contractions can be combined in a single group (with no spaces) with the predominant type of precipitation being first. In this single group, the intensity refers to the total precipitation and can be used with either one or no intensity qualifier, as appropriate. In TAFs, the intensity qualifiers (light, moderate, and heavy) refer to the intensity of the precipitation and not to the intensity of any thunderstorms associated with the precipitation.
Intensity is coded with precipitation types, except ice crystals and hail, including those associated with thunderstorms and those of a showery nature (SH). No intensity is ascribed to blowing dust (BLDU), blowing sand (BLSA), or blowing snow (BLSN). Only moderate or heavy intensity is ascribed to sandstorm (SS) and duststorm (DS).
7.2.2.8.1 Exception for Encoding Multiple Precipitation Types When more than one type of precipitation is forecast in a time period, any precipitation type associated with a descriptor (e.g., FZRA) is encoded first in the precipitation group, regardless of the predominance or intensity of the other precipitation types. Descriptors are not encoded with the second or third precipitation type in the group. The intensity is associated with the first precipitation type of a multiple precipitation type group. For example, a forecast of moderate snow and light freezing rain is coded as -FZRASN although the intensity of the snow is greater than the freezing rain.
Examples:
Combinations of one precipitation and one non-precipitation weather phenomena:
-DZ FG Light drizzle and fog (obstruction which reduces visibility to less than 5/8 SM)
RA BR Moderate rain and mist
-SHRA FG Light rain showers and fog
+SN FG Heavy snow and fog
Combinations of more than one type of precipitation:
-RASN FG HZ Light rain and snow (light rain predominant), fog and haze
TSSNRA Thunderstorm with moderate snow and rain (moderate snow predominant)
FZRASNPL
Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-27 Moderate freezing rain, snow, and ice pellets (freezing rain mentioned first due to the descriptor, followed by other precipitation types in order of predominance)
SHSNPL Moderate snow showers and ice pellets
7.2.2.8.2 Thunderstorm Descriptor The TS descriptor is treated differently than other descriptors in the following cases:
When non-precipitating thunderstorms are forecast, TS may be encoded as the sole significant weather phenomenon; and
When forecasting thunderstorms with freezing precipitation (FZRA or FZDZ), the TS descriptor is included first, followed by the intensity and weather phenomena.
Example:
TS -FZRA When a thunderstorm is included in the significant weather group (even using vicinity - VCTS), the cloud group (NsNsNshshshs) includes a forecast cloud type of CB. See the following example for encoding VCTS.
Example
-FZRA VCTS BKN010CB
7.2.2.8.3 Fog Forecast A visibility threshold must be met before a forecast for fog (FG) is included in the TAF. When forecasting a fog-restricted visibility from 5/8SM to 6SM, the phenomena is coded as BR (mist).
When a fog-restricted visibility is forecast to result in a visibility of less than 5/8SM, the code FG is used. The forecaster never encodes weather obstruction as mist (BR) when the forecast visibility is greater than 6 statute miles (P6SM).
The following fog-related terms are used as described below:
Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-28
Table 7-4. TAF Fog Terms
TERM DESCRIPTION Freezing Fog (FZFG) Any fog (visibility less than 5/8 SM) consisting predominantly of water droplets at temperatures less than or equal to 32o F/0oC, whether or not rime ice is expected to be deposited. FZBR is not a valid significant weather combination and will not be used in TAFs.
Shallow Fog (MIFG) The visibility at 6 feet above ground level is greater than or equal to 5/8 SM and the apparent visibility in the fog layer is less than 5/8 SM.
Patchy Fog (BCFG) Fog patches covering part of the airport. The apparent visibility in the fog patch or bank is less than 5/8 SM, with the foggy patches extending to at least 6 feet above ground level.
Partial Fog (PRFG) A substantial part of the airport is expected to be covered by fog while the remainder is expected to be clear of fog (e.g., a fog bank). NOTE:
MIFG, PRFG and BCFG may be forecast with prevailing visibility of P6SM.
Examples:
1/2SM FG Fog is reducing visibilities to less than 5/8SM, therefore FG is used to encode the fog.
3SM BR Fog is reducing visibilities to between 5/8 and 6SM, therefore BR is used to encode the fog.
7.2.2.9 Vicinity (VC) In the United States, vicinity (VC) is defined as a donut-shaped area between 5 and 10SM from the center of the airport’s runway complex. The FAA requires TAFs to include certain meteorological phenomena which may directly affect flight operations to and from the airport.
Therefore, NWS TAFs may include a prevailing condition forecast of fog, showers and thunderstorms in the airport's vicinity. A prevailing condition is defined as a greater than or equal to 50% probability of occurrence for more than ½ of the sub-divided forecast time period.
VC is not included in TEMPO or PROB groups.
The significant weather phenomena in Table 7-5 are valid for use in prevailing portions of NWS TAFs in combination with VC:
Table 7-5: TAF Use of Vicinity (VC) Phenomenon Coded Fog* VCFG Shower(s)** VCSH Thunderstorm VCTS * Always coded as VCFG regardless of visibility in the obstruction, and without qualification as to intensity or type (frozen or liquid)
** The VC group, if used, should be the last entry in any significant weather group (w'w')
Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-29
7.2.2.10 Cloud and Vertical Obscuration Groups The initial time period and any subsequent FM groups include a cloud or obscuration group (NsNsNshshshs, VVhshshs or SKC), used as appropriate to indicate the cumulative amount (NsNsNs) of all cloud layers in ascending order and height (hshshs), to indicate vertical visibility (VVhshshs) into a surface-based obstructing medium, or to indicate a clear sky (SKC).
All cloud layers and obscurations are considered opaque
7.2.2.10.1 Cloud Group The cloud group (NsNsNshshshs) is used to forecast cloud amount in Table 7-6.
Table 7-6. TAF Sky Cover
SKY COVER CONTRACTION SKY COVERAGE SKC 0 oktas FEW 0 to 2 oktas SCT 3 to 4 oktas BKN 5 to 7 oktas OVC 8 oktas
When zero (0) oktas of sky coverage is forecast, the cloud group is replaced by SKC. The contraction CLR, which is used in the METAR code, is not used in TAFs. TAFs for sites with ASOS/AWOS contain the cloud amount and/or obscurations which the forecaster expects, not what is expected to be reported by an ASOS/AWOS.
Heights of clouds (hshshs) are forecast in hundreds of feet AGL.
The lowest level at which the cumulative cloud cover equals 5/8 or more of the celestial dome is understood to be the forecast ceiling. For example, VV008, BKN008 or OVC008 all indicate an 800 ft ceiling.
7.2.2.10.2 Vertical Obscuration Group The vertical obscuration group (VVhshshs) is used to forecast, in hundreds of feet AGL, the vertical visibility (VV) into a surface-based total obscuration. VVhshshs is this ceiling at the height indicated in the forecast. TAFs do not include forecasts of partial obscurations (i.e., FEW000, SCT000, or BKN000).
Example:
1SM BR VV008 Ceiling is 800 feet due to vertical visibility into fog
7.2.2.10.3 Cloud Type The only cloud type included in the TAF is CB. CB follows cloud or obscuration height (hshshs) without a space whenever thunderstorms are included in significant weather group (w’w’), even if thunderstorms are only forecast in the vicinity (VCTS). CB can be included in the cloud group (NsNsNshshshs) or the vertical obscuration group (VVhshshs) without mentioning thunderstorm in the significant weather group (w'w’). Therefore, situations may occur where nearly identical NsNsNshshshs or VVhshshs appear in consecutive time periods, with the only change being the addition or elimination of CB in the forecast cloud type.
Examples:
Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-30
1/2SM TSRA OVC010CB Thunderstorms are forecast at the airport
7.2.2.11 Non-Convective Low-Level Wind Shear (LLWS) Group Wind Shear (WS) is defined as a rapid change in horizontal wind speed and/or direction, with distance and/or a change in vertical wind speed and/or direction with height. A sufficient difference in wind speed, wind direction, or both, can severely impact airplanes, especially within 2,000 feet AGL because of limited vertical airspace for recovery.
Forecasts of LLWS in the TAF refer only to non-convective LLWS from the surface up to and including 2,000 feet AGL. LLWS is always assumed to be present in convective activity. LLWS is included in TAFs on an “as-needed” basis to focus the aircrew’s attention on LLWS problems which currently exist or are expected. Non-convective LLWS may be associated with the following: frontal passage, inversion, low-level jet, lee side mountain effect, sea breeze front, Santa Ana winds, etc.
When LLWS conditions are expected, the non-convective LLWS code WS is included in the TAF as the last group (after cloud forecast). Once in the TAF, the WS group remains the prevailing condition until the next FM change group or the end of the TAF valid period if there are no subsequent FM groups. Forecasts of non-convective LLWS are not included in TEMPO or PROB groups.
The format of the non-convective low-level wind shear group is:
WShwshwshws/dddffKT
WS - Indicator for non-convective LLWS hwshwshws - Height of the top of the WS layer in hundreds of feet AGL ddd - True direction in ten degree increments at the indicated height -- VRB is not used for direction in the non-convective LLWS forecast group.
ff - Speed in knots of the forecast wind at the indicated height KT - Unit indicator for wind
Example:
TAF…13012KT…WS020/27055KT Wind shear from the surface to 2,000 feet. Surface winds from 130 (southeast) at 12 knots changes to 270 (west) at 55 knots at 2,000 feet.
In this example the indicator WS is followed by a three-digit number which is the top of the wind shear layer. LLWS is forecast to be present from the surface to this level. After the solidus /, the five digit wind group is the wind direction and speed at the top of the wind shear layer. It is not a value for the amount of shear.
A non-convective LLWS forecast is included in the initial time period or a FM group in a TAF whenever:
One or more PIREPs are received of non-convective LLWS within 2,000 feet of the surface, at or in the vicinity of the TAF airport, causing an indicated air speed loss or
Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-31 gain of 20 knots or more, and the forecaster determines the report(s) reflect a valid nonconvective LLWS event rather than mechanical turbulence, or
When non-convective vertical WS of 10 knots or more per 100 feet in a layer more than 200 feet thick are expected or reliably reported within 2,000 feet of the surface at, or in the vicinity of, the airport.
7.2.2.12 Forecast Change Indicator Groups Forecast change indicator groups are contractions which are used to sub-divide the forecast period (24-hours for scheduled TAFs; less for amended or delayed forecasts) according to significant changes in the weather.
The forecast change indicators, FM, TEMPO, and PROB, are used when a change in any or all of the elements forecast is expected:
7.2.2.12.1 From (FM) Group (FMGGgg) The change group FMGGgg (voiced as “from”) is used to indicate when prevailing conditions are expected to change significantly over a period of less than one hour. In these instances, the forecast is sub-divided into time periods using the contraction FM, followed, without a space, by four digits indicating the time (in hours and minutes Z) the change is expected to occur. While the use of a four-digit time in whole hours (e.g. 2100Z) is acceptable, if a forecaster can predict changes and/or events with higher resolution, then more precise timing of the change to the minute will be indicated. All forecast elements following FMGGgg relate to the period of time from the indicated time (GGgg) to the end of the valid period of the terminal forecast, or to the next FM if the terminal forecast valid period is divided into additional periods.
The FM group will be followed by a complete description of the weather (i.e., self-contained) and all forecast conditions given before the FM group are superseded by those following the group.
All elements of the TAF (surface wind, visibility, significant weather, clouds, obscurations, and when expected, non-convective LLWS) will be included in each FM group, regardless if they are forecast to change or not. For example, if forecast cloud and visibility changes warrant a new FM group but the wind does not, the new FM group will include a wind forecast, even if it is the same as the most recently forecast wind.
The only exception to this involves the significant weather group. If no significant weather is expected in the FM time period group, then significant weather group is omitted. A TAF may include one or more FM groups, depending on the prevailing weather conditions expected. In the interest of clarity, each FM group starts on a new line of forecast text, indented five spaces.
Examples:
TAF KDSM 022336Z 030024 20015KT P6SM BKN015 FM0230 29020G35KT 1SM +SHRA OVC005 TEMPO 0304 30030G45KT 3/4SM -SHSN FM0500 31010G20KT P6SM SCT025...
A change in the prevailing weather is expected at 0230 UTC and 0500 UTC.
TAF KAPN 312330Z 010024 13008KT P6SM SCT030
Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-32 FM0320 31010KT 3SM -SHSN BKN015 FM0500 31010KT 1/4SM +SHSN VV007...
Note the wind in the FM0500 group is the same as the previous FM group, but is repeated since all elements are required to be included in a FM group.
7.2.2.12.2 TEMPO GGGeGe The change-indicator group TEMPO GGGeGe is used to indicate temporary fluctuations to forecast meteorological conditions which are expected to:
Have a high percentage (greater than 50%) probability of occurrence, Last for one hour or less in each instance and, In the aggregate, cover less than half of the period GG to GeGe
Temporary changes described by TEMPO groups occur during a period of time defined by a two-digit beginning and two-digit ending time, both in whole hours UTC.
Each TEMPO group is placed on a new line in the TAF. The TEMPO identifier is followed by a description of all the elements in which a temporary change is forecast. A previously forecast element which has not changed during the TEMPO period is understood to remain the same and will not be included in the TEMPO group. Only those weather elements forecast to temporarily change are required to be included in the TEMPO group.
TEMPO groups will not include forecasts of either significant weather in the vicinity (VC) or nonconvective LLWS.
Examples:
TAF KDDC 221130Z 221212 29010G25KT P6SM SCT025 TEMPO 1517 30025G35KT 1 1/2SM SHRA BKN010...
In the example, all forecast elements in the TEMPO group are expected to be different than the prevailing conditions.
TAF KSEA 091125Z 091212 19008KT P6SM SCT010 BKN020 OVC090 TEMPO 1215 -RA SCT010 BKN015 OVC040...
In this example the visibility is not forecast in the TEMPO group. Therefore, the visibility is expected to remain the same (P6SM) as forecast in the prevailing conditions group. Also, note that in the TEMPO 1215 group, all three cloud layers are included, although the lowest layer is not forecast to change from the initial time period.
7.2.2.12.3 PROB30 GGGeGe The probability group, PROB30 GGGeGe, is only used by NWS forecasters to forecast a low probability occurrence (30% chance) of a thunderstorm or precipitation event and its associated weather and obscuration elements (wind, visibility and/or sky condition) at an airport.
The PROB30 group is the forecaster's assessment of probability of occurrence of the weather event which follows it. PROB30 is followed by a space, then four digits (GGGeGe) stating the
Aviation Weather Services, Advisory Circular 00-45F, Revision 1 AC 00-45F (July 2008) Section 7: Forecast Text Products Page 7-33 beginning and ending time (in hours) of the expected condition. PROB30 is the only PROB group used in NWS TAFs.
NOTE: U.S. military and international TAFs may use the PROB40 (40% chance) group as well.
The PROB30 group is located within the same line of the prevailing condition group, continuing on the line below if necessary.
The PROB30 group is not used in the first nine (9) hours of the TAF’s valid period, including amendments. PROB30 groups are six (6) hours or less in length. Only one PROB30 group is used following any subsequent FM groups.
PROB30 groups do not include forecasts of significant weather in the vicinity (VC) or nonconvective LLWS.
Example: