Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Table 7-5. 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.
7.2.2.8 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 7-6: 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')
AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-25
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
7.2.2.9 Cloud and Vertical Obscuration Groups (NsNsNshshshs or VVhshshs or SKC) The initial time period and any subsequent FM groups include a cloud or obscuration group (NsNsNshshshs or 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
7.2.2.9.1 Cloud Group (NsNsNshshshs) The cloud group (NsNsNshshshs) is used to forecast cloud amount in Table 7-6.
Table 7-7. 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.
7.2.2.9.2 Vertical Obscuration Group (VVhshshs) 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
7.2.2.9.3 Cloud Type (CB) 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:
AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-26
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
1/2SM TSRA OVC010CB Thunderstorms are forecast at the airport
7.2.2.10 Non-Convective Low-Level Wind Shear (LLWS) Group (WShwshwshws/dddffKT) 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 AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-27
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 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.
7.2.2.11 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:
7.2.2.11.1 From (FM) Group (FMYYGGgg) The change group FMYYGGgg (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 six digits, the first two of which indicate the day of the month and the final four which indicate 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 FMYYGGgg relate to the period of time from the indicated date and time (YYGGgg) 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 0300/0324 20015KT P6SM BKN015 FM030230 29020G35KT 1SM +SHRA OVC005 TEMPO 0303/0304 30030G45KT 3/4SM -SHSN FM030500 31010G20KT P6SM SCT025...
A change in the prevailing weather is expected on the 3rd day of the month at 0230 UTC and the 3rd day of the month at 0500 UTC.
AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-28
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) TAF KAPN 312330Z FM010320 31010KT 3SM -SHSN BKN015 0100/0124 13008KT P6SM SCT030 FM010500 31010KT 1/4SM +SHSN VV007...
Note the wind in the FM010500 group is the same as the previous FM group, but is repeated since all elements are required to be included in a FM group.
7.2.2.11.2 TEMPO (YYGG/YeYeGeGe) Group The change-indicator group TEMPO YYGG/YeYeGeGe 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 YYGG to YeYeGeGe
The first two digits (YY) are the day of the month for the start of the TEMPO. The next two digits (GG) are the starting hour (UTC). After the solidus (/), the next two digits (YeYe) are the ending day of the month, while the last two digits (GeGe) are the ending hour (UTC) of the TEMPO period.
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 2212/231 TEMPO 2215/2217 30025G35KT 1 1/2SM SHRA BKN010...
2 29010G25KT P6SM SCT025
In the example, all forecast elements in the TEMPO group are expected to be different than the prevailing conditions. The TEMPO group is valid on the 17 from 1500 UTC to 1700 UTC.
TAF KSEA 091125Z 0912/101 TEMPO 0912/0915 -RA SCT010 BKN015 OVC040...
2 19008KT P6SM SCT010 BKN020 OVC090
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 0912/0915 group, all three cloud layers are included, although the lowest layer is not forecast to change from the initial time period.
AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-29
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
7.2.2.11.3 PROB30 (YYGG/YeYeGeGe) Group The probability group, PROB30 YYGG/YeYeGeGe, 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. The first two digits (YY) are the day of the month for the start of the PROB30. The next two digits (GG) are the starting hour (UTC). After the solidus (/), the next two digits (YeYe) are the ending day of the month, while the last two digits (GeGe) are the ending hour (UTC) of the PROB30 period. PROB30 is the only PROB group used in NWS TAFs. Note that 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 may not be used in the first nine (9) hours of the TAF’s valid period, including amendments. Also, only one PROB30 group may be used in the initial forecast period and in any subsequent FM groups. Note that U.S. military and international TAFs do not have these restrictions.
PROB30 groups do not include forecasts of significant weather in the vicinity (VC) or nonconvective LLWS.
Example:
FM012100 18015KT P6SM SCT050 PROB30 0123/0201 2SM TSRA OVC020CB
In this example, the PROB30 group is valid on the 1st day of the month at 2300 UTC to the 2nd day of the month at 0100 UTC.
AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-30
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
7.2.2.12 TAF Examples
TAF KPIR 111140Z 1112/1212 13012KT P6SM BKN100 WS020/35035KT TEMPO 1112/1114 5SM BR FM111500 16015G25KT P6SM SCT040 BKN250 FM120000 14012KT P6SM BKN080 OVC150 PROB30 1200/1204 3SM TSRA BKN030CB FM120400 14008KT P6SM SCT040 OVC080 TEMPO 1204/1208 3SM TSRA OVC030CB
TAF Terminal Aerodrome Forecast KPIR Pierre, South Dakota 111140 prepared on the 11 th at 1140 UTC 1112/1212 valid from the 11 th at 1200 UTC until the 12th at 1200 UTC 13012KT wind 130 at 12 knot s P6SM visibility greater than 6 statute miles BKN100 ceiling 10,000 broken WS020/35035KT wind shear at 2,000 feet, wind from 350 at 35 knots TEMPO 1112/1114 temporary conditions between the 11th day of the month at 1200 UTC and the 11th day of the month at 1400 UTC 5SM visibility 5 statute miles BR mist FM111500 from the 11 th day of the month at 1500 UTC 16015G25KT wind 160 at 15 knots gusting to 25 knots P6SM visibility greater than 6 statute miles SCT040 BKN250 4,000 scattered, ceiling 25,000 broken FM120000 from the 12 th day of the month at 0000Z 14012KT wind 140 at 12 knot s P6SM visibility greater than 6 statute miles BKN080 OVC150 ceiling 8,000 broken, 15,000 overcast PROB30 1200/1204 30% probability between the 12th day of the month at 0000 UTC and the 12th day of the month at 0400 UTC 3SM visibility 3 statute miles TSRA thunderstorm with moderate rain showers BKN030CB ceiling 3,000 broken with cumulonimbus FM120400 from the 12 th day of the month at 0400 UTC 14008KT wind 140 at 8 knot s P6SM visibility greater than 6 statute miles SCT040 OVC080 4,000 scattered, ceiling 8,000 overcast TEMPO 1204/1208 temporary conditions between the 12th day of the month at 0400 UTC and the 12th day of the month at 0800 UTC 3SM visibility 3 statute miles TSRA thunderstorms with moderate rain showers OVC030CB ceiling 3,000 overcast with cumulonimbus
AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-31
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
TAF AMD KEYW 131555Z 1316/1412 VRB03KT P6SM VCTS SCT025CB BKN250 TEMPO 1316/1318 2SM TSRA BKN020CB FM131800 VRB03KT P6SM SCT025 BKN250 TEMPO 1320/1324 1SM TSRA OVC010CB FM140000 VRB03KT P6SM VCTS SCT020CB BKN120 TEMPO 1408/1412 BKN020CB
TAF AMD Amended Terminal Aerodrome Forecast KEYW Key West, Florida 131555Z prepared on the 13 th at 1555 UTC 1316/1412 valid from the 13 th at 1600 UTC until the 14th at 1200 UTC VRB03KT wind variable at 3 knot s P6SM visibility greater than 6 statute miles VCTS thunderstorms in the vicinity SCT025CB BKN250 2,500 scattered with cumulonimbus, ceiling 25,000 broken TEMPO 1316/1318 temporary conditions between the 13th day of the month at 1600 UTC and the 13th day of the month at 1800 UTC 2SM visibility 2 statute miles TSRA thunderstorms with moderate rain showers BKN020CB ceiling 2,000 broken with cumulonimbus FM131800 from the 13 th day of the month at 1800 UTC VRB03KT wind variable at 3 knot s P6SM visibility greater than 6 statute miles SCT025 BKN250 2,500 scattered, ceiling 25,000 broken TEMPO 1320/1324 temporary conditions between the 13th day of the month at 2000 UTC and the 14th day of the month at 0000 UTC 1SM visibility 1 statute mile TSRA thunderstorms with moderate rain showers OVC010CB ceiling 1,000 overcast with cumulonimbus FM140000 from the 14 th day of the month at 0000 UTC VRB03KT variable wind at 3 knot s P6SM visibility greater than 6 statute miles VCTS thunderstorms in the vicinity SCT020CB BKN120 2,000 scattered with cumulonimbus, ceiling 12,000 broken TEMPO 1408/1412 temporary conditions between the 14th day of the month at 0800 UTC and the 14th day of the month at 1200 UTC BKN020CB ceiling 2,000 broken with cumulonimbus AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-32
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
TAF KCRP 111730Z 1118/1218 19007KT P6SM SCT030 TEMPO 1118/1120 BKN040 FM112000 16011KT P6SM VCTS FEW030CB SCT250 FM120200 14006KT P6SM FEW025 SCT250 FM120800 VRB03KT 5SM BR SCT012 FM121500 17007KT P6SM SCT025
TAF Terminal Aerodrome Forecast KCRP Corpus Christi, Texas 111730Z prepared on the 11 th at 1730 UTC 1118/1218 valid from the 11 th at 1800 UTC until the 12th at 1800 UTC 19007KT wind 190 at 7 knot s P6SM visibility greater than 6 statute miles SCT030 3,000 scattered TEMPO 1118/1120 temporary conditions between 1800 UTC and 2000 UTC on the 11th.
BKN040 ceiling 4,000 broken FM112000 from the 11 th day of the month at 2000 UTC 16011KT wind 160 at 11 knot s P6SM visibility greater than 6 statute miles VCTS thunderstorms in the vicinity FEW030CB SCT250 3,000 few with cumulonimbus, 25,000 scattered FM120200 from the 12 th day of the month at 0200 UTC 14006KT wind 140 at 6 knot s P6SM visibility greater than 6 statute miles FEW025 SCT250 2,500 few, 25,000 scattered FM120800 from the 12 th day of the month at 0800 UTC VRB03KT wind variable at 3 knot s 5SM visibility 5 statute miles BR mist SCT012 1,200 scattered FM121500 from the 12 th day of the month at 1500 UTC 17007KT wind 170 at 7 knot s P6SM visibility greater than 6 statute miles SCT025 2,500 scattered
7.2.3 Issuance Scheduled TAFs prepared by NWS offices are issued four times a day, every six (6) hours, according to the following schedule:
Table 7-8. TAF Issuance Schedule
SCHEDULED ISSUANCE VALID PERIOD ISSUANCE WINDOW 0000 UTC 0000 to 2400 UTC 2320 to 2340 UTC 0600 UTC 0600 to 0600 UTC 0520 to 0540 UTC 1200 UTC 1200 to 1200 UTC 1120 to 1140 UTC 1800 UTC 1800 to 1800 UTC 1720 to 1740 UTC AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-33
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
7.2.3.1 Minimum Observational Requirements for Routine TAF Issuance and Continuation The NWS WFO aviation forecaster must have certain information for the preparation and scheduled issuance of each individual TAF. Although integral to the TAF writing process, a complete surface (METAR/SPECI) observation is not required. Forecasters use the "total observation concept" to write TAFs with data including nearby surface observations, radar, satellite, radiosonde, model data, aircraft, and other sources.
If information sources, such as surface observations, are missing, unreliable, or not complete, forecasters will append AMD NOT SKED to the end of a TAF. The use of AMD NOT SKED indicates the forecaster has enough data, using the total observation concept, to issue a forecast but will not provide updates. This allows airport operations to continue using a valid TAF.
In rare situations where observations have been missing for extended periods of time (i.e., more than one TAF cycle of six hours), and the total observation concept cannot provide sufficient information, the TAF may be suspended by the use of NIL TAF.
7.2.3.2 Sites with Scheduled Part-Time Observations For TAFs with less than 24-hour observational coverage, the TAF will be valid to the end of the routine scheduled forecast period even if observations cease prior to that time. The time observations are scheduled to end and/or resume will be indicated by expanding the AMD NOT SKED statement. Expanded statements will include the observation ending time (AFT Y1Y1HHmm, e.g., AFT 120200), the scheduled observation resumption time (TIL Y1Y1HHmm,
e.g., TIL 171200Z) or the period of observation unavailability (Y1Y1HH/YeYehh, e.g., 2502-2512).
TIL will be used only when the beginning of the scheduled TAF valid period coincides with the time of the last observation or when observations are scheduled to resume prior to the next scheduled issuance time. When used, these remarks will immediately follow the last forecast group. If a routine TAF issuance is scheduled to be made after observations have ceased, but before they resume, the remark AMD NOT SKED will immediately follow the valid period group of the scheduled issuance. After sufficient data using the total observation concept has been received, the AMD NOT SKED remark will be removed.
7.2.3.2.1 Examples of Scheduled Part-Time Observations TAFs
TAF AMD KRWF 150202Z 1502/1524 {TAF text} AMD NOT SKED 1505Z-1518Z= No amendments will be available between the 15th day of the month at 0500 UTC and the 15th day of the month at 1800 UTC due to lack of a complete observational set between those times.
TAF AMD KPSP 190230Z 1903/1924 {TAF text} AMD NOT SKED= Amendments are not scheduled.
AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-34
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
7.2.3.3 Automated Observing Sites Requiring Part-Time Augmentation TAFs for AWOS-III sites which have part-time augmentation are prepared using the procedures for part-time manual observation sites detailed in the previous section, with one exception. This exception is the remark used when the automated system is unattended. Specifically, the time an augmented automated system is scheduled to go into unattended operation and/or the time augmentation resumes is included in a remark unique to automated observing sites: AMD LTD TO CLD VIS AND WIND (AFT YYHHmm, or TIL YYhhmm, or YYHH-YYhh), where YY is the date, HHmm is the time, in hours and minutes, of last augmented observation and hhmm is the time, in hours and minutes, the second complete observation is expected to be received. This remark, which does not preclude amendments for other forecast elements, is appended to the last scheduled TAF issued prior to the last augmented observation. It will also be appended to all subsequent amendments until augmentation resumes.
The AMD LTD TO (elements specified) remark is a flag for users and differs from the AMD NOT SKED AFT Z remark for part-time manual observation sites. AMD LTD TO (elements specified) means users should expect amendments only for those elements and the times specified.
Example:
TAF AMD KCOE 150202Z 1502/1524 text AMD LTD TO CLD VIS AND WIND 1505-1518=
The amended forecast indicates that amendments will only be issued for wind, visibility and clouds, between the 15th day of the month at 0500Z and the 15th day of the month at 1800Z.
An amendment includes forecasts for all appropriate TAF elements, even those not reported when the automated site is not augmented. If unreported elements are judged crucial to the TAF and cannot be adequately determined (e.g., fog versus moderate snow), the TAF will be suspended (i.e. an amended TAF stating ”AMD NOT SKED”).
AWOS-III systems with part-time augmentation, which the forecaster suspects are providing unreliable information when not augmented, will be reported for maintenance and treated the same as part-time manual observation sites. In such cases, the AMD NOT SKED AFT YY/aaZ remark will be used.
7.2.3.4 Non-Augmented Automated Observing Sites The TAF issued for a non-augmented ASOS site may be suspended in the event the forecaster is notified of, or strongly suspects, an outage or unrepresentative data. Forecasters may also suspend TAF amendments when an element the forecaster judges to be critical is missing from the observation and cannot be obtained using the total observation concept. The term AMD NOT SKED will be appended, on a separate line and indented five spaces, to the end of an amendment to the existing TAF when appropriate.
AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-35
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
7.3 International Aviation Route Forecasts (ROFOR) International ROFORs are prepared and issued several hours in advance of regularly scheduled flights. The only NWS office which routinely issues ROFORs is the Weather Forecast Office (WFO) in Honolulu due to its designation as an ICAO Meteorological Watch Office (MWO).
7.3.1 ROFOR Criteria WFO Honolulu will honor all ROFOR requests for flights within the Pacific Region beginning or ending in, or having most of the flight path within its area of responsibility, which is the Oakland Oceanic FIR south of 30N, between 140W and 130E.
7.3.2 Issuance ROFORs are issued for prescribed times, several hours in advance, for regularly scheduled flights. ROFOR requests for unscheduled flights are prepared as soon as time allows.
7.3.2.1 ROFOR Amendments ROFORs are not required to be amended.
7.3.2.2 ROFOR Corrections ROFOR corrections are issued as soon as possible when erroneous data has been transmitted.
7.3.3 ROFOR Content ROFORs contain some or all of the following forecast parameters:
• Winds and temperatures aloft
• Significant en-route weather
• Zone weather
• Weather Synopsis
At a minimum, ROFORs include the first two bullets. They may contain data for multiple altitudes and include TAFs for destination points and/or alternates.
The core of a ROFOR is formatted as follows: 0iQLL 4hhhTT ddFFF
Where i = 1 for zone up to latitude L i = 2 for zone up to longitude LL
Q = 1 east of the dateline in the northern hemisphere Q = 2 west of the dateline in the northern hemisphere Q = 6 east of the dateline in the southern hemisphere Q = 7 west of the dateline in the southern hemisphere
hhh = height to which the temperature and wind refer TT = air temperature in whole degrees Celsius at hhh dd = true direction in tens of degrees from which the wind will blow at hhh AC 00-45F, CHG 2 Section 7: Forecast Text Products Page 7-36