5-100 A Non-Convective LLWS forecast is included in the initial time period or a FM group in a TAF whenever:
• One or more Pilot Weather Reports (PIREP) are received of Non-Convective LLWS within 2,000 ft of the surface, at or in the vicinity of the TAF airport, causing an indicated air speed loss or gain of 20 kts or more, and the forecaster determines the report(s) reflect a valid Non-Convective LLWS event rather than mechanical turbulence; or
• When Non-Convective vertical WS of 10 kts or more per 100 ft in a layer more than 200 ft thick are expected or reliably reported within 2,000 ft of the surface at, or in the vicinity of, the airport.
5.13.2.12 Forecast Change Indicator Groups.
Forecast change indicator groups are contractions that are used to subdivide 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.
5.13.2.12.1 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 1 hour. In these instances, the forecast is subdivided 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(i.e., self-contained), and all forecast conditions given before the FM group are superseded by those following the group.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
5-101 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.
TAF KAPN 312330Z 0100/0124 13008KT P6SM SCT030 FM010320 31010KT 3SM -SHSN BKN015 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.
5.13.2.12.2 TEMPO (YYGG/YeYeGeGe) Group.
The change-indicator group TEMPO YYGG/YeYeGeGe is used to indicate temporary fluctuations to forecast meteorological conditions that are expected to:
• Have a high percentage (greater than 50 percent) 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 that 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.
5-102 TEMPO groups will not include forecasts of either significant weather in the vicinity (VC) or Non-Convective LLWS.
Examples:
TAF KDDC 221130Z 2212/2312 29010G25KT P6SM SCT025 TEMPO 2215/2217 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. The TEMPO group is valid on the 17 from 1500 UTC to 1700 UTC.
TAF KSEA 091125Z 0912/1012 19008KT P6SM SCT010 BKN020 OVC090 TEMPO 0912/0915 -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 0912/0915 group, all three cloud layers are included, although the lowest layer is not forecast to change from the initial time period.
5.13.2.12.3 PROB30 (YYGG/YeYeGeGe) Group.
The probability group, PROB30 YYGG/YeYeGeGe, is only used by NWS forecasters to forecast a low probability occurrence (30 percent chance) of a thunderstorm or precipitation event and its associated weather and obscuration elements (wind, visibility, and/or sky condition) at an airport.
The PRO B30 group is the forecaster’s assessment of probability of occurrence of the weather event that 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 percent 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.
NWS TAFs do not use the PROB30 group in the first 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.
5-103 PROB30 groups do not include forecasts of significant weather in the vicinity (VC) or Non-Convective 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.
5.13.2.12.4 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 11th at 1140 UTC 1112/1212 Valid from the 11th at 1200 UTC until the 12th at 1200 UTC 13012KT Wind 130 at 12 kts P6SM Visibility greater than 6 sm BKN100 Ceiling 10,000 broken WS020/35035KT Windshear at 2,000 ft, wind from 350 at 35 kts TEMPO 1112/1114 Temporary conditions between the 11 th 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 11th day of the month at 1500 UTC 16015G25KT Wind 160 at 15 kts gusting to 25 kts P6SM Visibility greater than 6 sm SCT040 BKN250 4,000 scattered, ceiling 25,000 broken FM120000 From the 12th day of the month at 0000Z 14012KT Wind 140 at 12 kts P6SM Visibility greater than 6 sm BKN080 OVC150 Ceiling 8,000 broken, 15,000 overcast PROB30 1200/1204 30 percent probability between the 12 th day of the month at 0000 UTC and the 12th day of the month at 0400 UTC 3SM Visibility 3 sm TSRA Thunderstorm with moderate rain showers
5-104 BKN030CB Ceiling 3,000 broken with cumulonimbus FM120400 From the 12th day of the month at 0400 UTC 14008KT Wind 140 at 8 kts P6SM Visibility greater than 6 sm SCT040 OVC080 4,000 scattered, ceiling 8,000 overcast TEMPO 1204/1208 Temporary conditions between the 12 th day of the month at 0400 UTC and the 12th day of the month at 0800 UTC 3SM Visibility 3 sm TSRA Thunderstorms with moderate rain showers OVC030CB Ceiling 3,000 overcast with cumulonimbus
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 13th at 1555 UTC 1316/1412 Valid from the 13th at 1600 UTC until the 14th at 1200 UTC VRB03KT Wind variable at 3 kts P6SM Visibility greater than 6 sm VCTS Thunderstorms in the vicinity SCT025CB BKN250 2,500 scattered with cumulonimbus, ceiling 25,000 broken TEMPO 1316/1318 Temporary conditions between the 13 th day of the month at 1600 UTC and the 13th day of the month at 1800 UTC 2SM Visibility 2 sm TSRA Thunderstorms with moderate rain showers BKN020CB Ceiling 2,000 broken with cumulonimbus FM131800 From the 13th day of the month at 1800 UTC VRB03KT Wind variable at 3 knots P6SM Visibility greater than 6 sm SCT025 BKN250 2,500 scattered, ceiling 25,000 broken TEMPO 1320/1324 Temporary conditions between the 13 th day of the month at 2000 UTC and the 14th day of the month at 0000 UTC 1SM Visibility 1 sm TSRA Thunderstorms with moderate rain showers OVC010CB Ceiling 1,000 overcast with cumulonimbus FM140000 From the 14th day of the month at 0000 UTC VRB03KT Variable wind at 3 knots P6SM Visibility greater than 6 sm VCTS Thunderstorms in the vicinity
5-105 SCT020CB BKN120 2,000 scattered with cumulonimbus, ceiling 12,000 broken TEMPO 1408/1412 Temporary conditions between the 14 th day of the month at 0800 UTC and the 14th day of the month at 1200 UTC BKN020CB Ceiling 2,000 broken with cumulonimbus
5.13.3 Issuance.
Scheduled TAFs prepared by NWS offices are issued four times a day, every 6 hours, according to the following schedule:
Table 5-19. TAF Issuance Schedule
SCHEDULED ISSUANCE VALID PERIOD ISSUANCE WINDOW 0000 UTC 0000 to 2400 or 0600 UTC 2320 to 2340 UTC 0600 UTC 0600 to 0600 or 1200 UTC 0520 to 0540 UTC 1200 UTC 1200 to 1200 or 1800 UTC 1120 to 1140 UTC 1800 UTC 1800 to 1800 or 2400 UTC 1720 to 1740 UTC
5.13.3.1 Minimum Observational Requirements for Routine TAF Issuance and Continuation.
The NWS 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 6 hours), and the total observation concept cannot provide sufficient information, the TAF may be suspended by the use of NIL TAF.
5.13.3.2 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
5-106 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.
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.
5.13.3.3 Automated Observing Sites Requiring Part-Time Augmentation.
TAFs for automated stations without present weather and obstruction to vision information and have no augmentation or only part-time augmentation, are prepared using the procedures for part-time manual observation sites detailed in the previous paragraph, 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.
5-107 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 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.
5.13.3.4 Non-Augmented Automated Observing Sites.
The TAF issued for automated observing stations with no augmentation 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.
5.14 Route Forecasts (ROFOR).
5.14.1 Issuance.
ROFORs are only issued by the NWS WFO in Honolulu, HI, twice per day for two routes: San Francisco, CA (KSFO), to Honolulu, HI (PHNL), and Santa Barbara, CA (KSBA), and PHNL. ROFORs are available on the NWS WFO Honolulu website.
5.14.2 ROFOR Amendments.
ROFORs are not required to be amended.
5.14.3 ROFOR Corrections.
ROFOR corrections are issued as soon as possible when erroneous data has been transmitted.
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5.14.4 ROFOR Content.
ROFORs contain some or all of the following forecast parameters, which are valid for the specified times:
• Winds and temperatures aloft at flight levels (FL) 050, 100, 180 and 240 (true direction in tens of degrees, speed in knots, air temperature in whole degrees Celsius with P for a value above 0 and M for a value below zero).
• Significant en route weather.
• Zone weather, in abbreviated code, for numbered zones (zone map available on NWS WFO Honolulu website).
o Cloud amount in oktas, cloud types, cloud bases. and tops (MSL or FL).
o Coverage and type of precipitation and weather along with visibility when below 7 sm.
• Overall wind factor component at FLs 050, 100, 180 and 240.
• Weather Synopsis.
Note: See Appendi ces A and B for definitions of common terms used in ROFORs.
5.14.5 Example.
5.14.5.1 Santa Barbara and San Francisco to Honolulu Route ROFOR Example.
FRPN31 PHFO 301857 RFRKSF
WINDS/TEMPERATURES AND WEATHER BY ZONE FOR ROUTE SFO/HNL VIA 31.3N/140W VALID AT 311200Z
FLIGHT LEVELS ZONE FL050 FL100 FL180 FL240 ZONE WEATHER 25 3315 P16 3208 P11 3109 M07 3216 M19 6-8 STSC 010/030 26 3316 P13 3211 P09 3117 M06 3023 M18 4-6 STSC 015/045 27 3013 P12 3212 P09 3020 M06 3024 M18 6-8 MERGING LYR TO 200 ISOL VIS 3-5SM RA ISOL TCU TOPS FL220 28 3008 P14 3008 P08 2815 M06 2918 M18 DO 29 9905 P14 9905 P08 2609 M06 2612 M18 4-6 CUSC 020/050 30 0506 P14 9905 P08 9905 M06 2406 M18 DO 31 0818 P15 0613 P09 0307 M06 9905 M18 4-6 CUSC 020/080
ISOL -SHRA 32 0822 P15 0719 P09 0711 M05 9905 M17 DO
OVERALL COMPONENTS P4 P2 M4 M10 ROUTE SBA/HNL VIA 29.5N/140W VALID AT 311200Z
FLIGHT LEVELS ZONE FL050 FL100 FL180 FL240 ZONE WEATHER 25 3509 P17 3108 P11 3011 M07 3015 M19 6-8 STSC 010/030 26 3416 P14 3312 P09 3218 M05 3123 M18 4-6 STSC 015/045 27 0111 P13 3510 P10 3017 M05 3021 M18 2-4 CUSC 020/045 28 0307 P14 3606 P09 2713 M05 2717 M18 DO 29 0406 P14 9905 P08 2507 M05 2610 M18 4-6 CUSC 020/050 30 0815 P15 0610 P09 9905 M05 9905 M17 DO
5-109 31 0821 P15 0616 P09 0408 M05 9905 M18 4-6 CUSC 020/080
ISOL -SHRA 32 0822 P15 0719 P09 0812 M06 9905 M18 DO
OVERALL COMPONENTS P10 P5 M4 M7 SYNOPSIS...1024MB HIGH CENTERED NEAR N3000 W15600.
In the above example, for the route KSFO to PHNL, valid for 1200 UTC on the 31st of the month, for zone 25 the winds at FL050 (FLs, i.e., altimeter setting 29.92, are used when flying over the oceans) is at forecast are 330 degree (true) and 15 kts, temperature plus 16 Celsius. The Zone Weather for zone 25 is 6 to 8 oktas (i.e. BKN to OVC) cloud cover, stratus and stratocumulus cloud types, with bases 1,000 MSL and tops 3,000 MSL. The overall wind factor component at FL 050 is plus 4 kts. For zone 28, the “DO” stands for ditto and means that the zone weather is the same as the zone above, in this case zone 27.
5.15 Wind and Temperature Aloft.
There are many wind and temperature forecasts and products produced by the NWS.
Each NWP model outputs wind and temperature at multiple levels. The primary output of these forecasts is a gridded binary code format (e.g., GRIB2) intended for use in flight planning software.
This paragraph dis cusses one of the wind and temperature aloft forecast products, Wind and Temperature Aloft Forecasts (FB). Other paragraphs within this AC provide additional wind and temperature aloft forecasts, i.e., constant pressure level forecasts (see paragraph 5.17.1), and the global winds and temperature forecasts provided under the World Area Forecast System (WAFS) (see paragraph 5.20.1).
5.15.1 Wind and Temperature Aloft Forecast (FB).
Wind and Temperature Aloft Forecasts (FB) are computer-prepared forecasts of wind direction, wind speed, and temperature at specified times, altitudes, and locations. FBs are available on https://www.aviationweather.gov in both text and graphic format.
5.15.1.1 Issuance.
The NWS NCEP produces scheduled FB Wind and Temperature Aloft Forecasts four times daily for specified locations in the CONUS, the Hawaiian Islands, Alaska and coastal waters, and the western Pacific Ocean. Specified locations are documented on https://www.aviationweather.gov under ADDS Wind Temp Data Web page.
Amendments are not issued to the forecasts. Wind forecasts are not issued for altitudes within 1,500 ft of a location’s elevation. Temperature forecasts are not issued for altitudes within 2,500 ft of a location’s elevation.
5.15.1.2 Format.
The AWC’s website provides a graphical depiction of the FB wind and temperature forecasts as well as a text version.
5.15.1.2.1 Graphical Display.
The AWC's website provides an interactive display (see Figure 5-51, FB Wind and Temperature Aloft Interactive Display Example) of the FB wind and temperature forecasts.
Figure 5-51. FB Wind and Temperature Aloft Interactive Display Example ADDS Wind Temp Data INFO FB Wind Display at 9,000 feet valid at 0000 UTC 23 Apr 2015 GEG / LWS ¿ GOT FA PW M erstos ACK ACY 219RF HAT
AE LO ILM OHS 2XG Map: Plot Options: Data Options: Overlays:
•Light DHover 9,000ft • Level •Highways ODark 6 hr • Forecast _ Top Jetroutes O Simple CARTCC/FIR Bounds Wind @Calm ko 15knt L060knt The interactive graphic depicts wind speed (knots) and direction (referenced to true north) using standard windbarb display. Temperature (Celsius) is placed to the upper left of the station circle.
A click on the station displays the wind and temperature forecast and station three-letter identification in a separate text window. When the "Hover" option is selected, the wind and temperature text window appears by merely placing the cursor over the station.
5-110
5-111 Selected altitudes (3,000, 6,000, 9,000, 12,000, 18,000, 24,000, 30,000, 34,000, 39,000, 45,000, and 53,000 ft) and forecast valid times (6-, 12- and 24-hour) can be changed using the pulldown menus under “Data Options.”
5.15.1.2.2 Text Format.
Forecasts are provided for select altitudes and locations. Some locations have additional altitudes.
The text format for the FB wind and temperature forecasts uses the symbolic form DDff+TT in which DD is the wind direction, ff the wind speed, and TT the temperature.
Wind direction is indicated in tens of degrees (two digits) with reference to true north and wind speed is given in knots (two digits). Light and variable wind or wind speeds of less than 5 kts are expressed by 9900. Forecast wind speeds of 100 through 199 kts are indicated by subtracting 100 from the speed and adding 50 to the coded direction. For example, a forecast of 250 degrees, 145 kts, is encoded as 7545. Forecast wind speeds of 200 kts or greater are indicated as a forecast speed of 199 kts. For example, 7799 is decoded as 270 degrees at 199 kts or greater.
Temperature is indicated in degrees Celsius (two digits) and is preceded by the appropriate algebraic sign for the levels from 6,000 through 24,000 ft.
Above 24,000 ft, the sign is omitted since temperatures are always negative at those altitudes.
The product header includes the date and time observations were collected, the forecast valid date and time, and the time period during which the forecast is to be used.
5.15.1.2.3 Examples.
1312+05 The wind direction is from 130 degree (i.e., southeast), the wind speed is 12 kts, and the temperature is 5 ºCelsius.
9900+10 Wind light and variable, temperature +10 ºCelsius.
7735-07 The wind direction is from 270 degrees (i.e., west), the wind speed is 135 kts, and the temperature is minus 7 ºCelsius.