11/14/16 Aviation Weather Services AC 00-45H 5-92 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
5.11.3 Issuance.
Scheduled TAFs prepared by NWS offices are issued four times a day, every 6 hours, according to the following schedule:
Table 5-17. 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
5.11.3.1 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.
5.11.3.2 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.
11/14/16 Aviation Weather Services AC 00-45H 5-93 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.
5.11.3.3 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.
5.11.3.4 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.
11/14/16 Aviation Weather Services AC 00-45H 5-94 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.
5.11.3.5 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.
5.12 Route Forecasts (ROFOR).
5.12.1 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 Web site.
5.12.2 ROFOR Amendments.
ROFORs are not required to be amended.
5.12.3 ROFOR Corrections.
ROFOR corrections are issued as soon as possible when erroneous data has been transmitted.
11/14/16 Aviation Weather Services AC 00-45H 5-95
5.12.4 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 Web site).
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 Appendices A and B for definitions of common terms used in ROFORs.
5.12.5 Example.
5.12.5.1 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
11/14/16 Aviation Weather Services AC 00-45H 5-96 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.
5.13 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 discusses 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 5.15.1), and the global winds and temperature forecasts provided under the World Area Forecast System (WAFS) (see paragraph 5.17.1)
5.13.1 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 http://www.aviationweather.gov in both text and graphic format.
5.13.1.1 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 http://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.
5.13.1.2 Format.
The AWC’s Web site provides a graphical depiction of the FB wind and temperature forecasts as well as a text version.
11/14/16 Aviation Weather Services AC 00-45H
5.13.1.2.1 Graphical Display.
The AWC's Web site provides an interactive display (see Figure 5-43, FB Wind and Temperature Aloft Interactive Display Example) of the FB wind and temperature forecasts.
Figure 5-43. 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 1 3 050 K
LE-SEMLEG PW M ACK A CY WIL 210RF 1, 2RDUr HAT
A FLO ILM aHS BRO H51 H52 Map: Plot Options: Data Options: Overlays:
•Light •Hover 9,000ft ¢ Level OHighways ODark 6 hr Forecast OTop Jetroutes
• Simple DARTCC/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.
5-97
11/14/16 Aviation Weather Services AC 00-45H 5-98 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.”
5.13.1.2.2 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.
5.13.1.2.3 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.
11/14/16 Aviation Weather Services AC 00-45H 5-99
5.13.1.2.4 Coding Example.
Sample winds aloft text message:
DATA BASED ON 010000Z VALID 010600Z FOR USE 0500-0900Z. TEMPS NEG ABV 24000 FT 3000 6000 9000 12000 18000 24000 30000 34000 39000 MKC 9900 1709+06 2018+00 2130-06 2242-18 2361-30 247242 258848 550252 Sample message decoded:
DATA BASED ON 010000Z Forecast data is based on computer forecasts generated the first day of the month at 0000 UTC.
VALID 010600Z FOR USE 0500-0900Z. TEMPS NEG ABV 24000 The valid time of the forecast is the 1st day of the month at 0600 UTC. The forecast winds and temperature are to be used between 0500 and 0900 UTC.
Temperatures are negative above 24,000 ft.
FT 3000 6000 9000 12000 18000 24000 30000 34000 39000 FT indicates the altitude of the forecast.
MKC 9900 1709+06 2018+00 2130-06 2242-18 2361-30 247242 258848 550252 MKC indicates the location of the forecast. The rest of the data is the winds and temperature aloft forecast for the respective altitudes.
Table 5-18, Wind and Temperature Aloft Forecast Decoding Examples, shows data for MKC (Kansas City, MO).
11/14/16 Aviation Weather Services AC 00-45H 5-100 Table 5-18. Wind and Temperature Aloft Forecast Decoding Examples FT 3000 6000 9000 12000 18000 24000 30000 34000 39000 MKC 9900 1709+06 2018+00 2130-06 2242-18 2361-30 247242 258848 550252 Altitude (feet) Coded Wind Temperature (˚C) 3,000 FT 9900 Light and variable Not forecast 6,000 FT 1709+06 170 degrees at 9 knots +06 degrees Celsius 9,000 FT 2018+00 200 degrees at 18 knots Zero degrees Celsius 12,000 FT 2130-06 210 degrees at 30 knots -06 degrees Celsius 18,000 FT 2242-18 220 degrees at 42 knots -18 degrees Celsius 24,000 FT 2361-30 230 degrees at 61 knots -30 degrees Celsius 30,000 FT 247242 240 degrees at 72 knots -42 degrees Celsius 34,000 FT 258848 250 degrees at 88 knots -48 degrees Celsius 39,000 FT 750252 250 degrees at 102 knots -52 degrees Celsius
5.13.1.3 Use.
Table 5-19, Wind and Temperature Aloft Forecast (FB) Periods, provides the time periods for use of FB Wind and Temperature forecasts.
Table 5-19. Wind and Temperature Aloft Forecast (FB) Periods Model Run Product Available 6 hour Forecast 12 hour Forecast 24 hour Forecast Valid For Use Valid For Use Valid For Use 0000Z ~0200Z 0600Z 0200-0900Z 1200Z 0900-1800Z 0000Z 1800-0600Z 0600Z ~0800Z 1200Z 0800-1500Z 1800Z 1500-0000Z 0600Z 0000-1200Z 1200Z ~1400Z 1800Z 1400-2100Z 0000Z 2100-0600Z 1200Z 0600-1800Z 1800Z ~2000Z 0000Z 2000-0300Z 0600Z 0300-1200Z 1800Z 1200-0000Z
5.14 Freezing-Level Graphics.
The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0ºC. This altitude is also known as the height of the 0ºC constant-temperature surface. A freezing level graphics (see Figure 5-44, Aviationweather.gov Freezing Level Graphic—Example) show the height of the 0ºC constant-temperature surface.
11/14/16 Aviation Weather Services AC 00-45H 5-101 The concept of freezing level becomes slightly more complicated when more than one altitude is determined to be at a temperature of 0 ºC. These “multiple freezing layers” occur when a temperature inversion at altitudes above the defined freezing level are present. For example, if the first freezing level is at 3000 ft MSL and the second is at 7000 ft MSL, a temperature inversion is between these two altitudes. This would indicate temperatures rising above freezing above 3000 ft MSL and then back below freezing at 7000 ft MSL.
The AWC provides freezing-level graphics available on their Web site.
The freezing-level graphics provide an initial analysis and forecasts at specified times into the future. The forecasts are based on output from a NWS NCEP NWP.
5.14.1 Issuance.
The initial analysis and forecast graphics are updated hourly.
5.14.2 Format.
The colors represent the height in hundreds of feet above MSL of the lowest freezing level. Regions with white indicate the surface and the entire depth of the atmosphere are below freezing. Hatched or spotted regions (if present) represent areas where the surface temperature is below freezing with multiple freezing levels aloft.
5.14.3 Use.
Freezing-level graphics are used to assess the lowest freezing-level heights and their values relative to flight paths. Clear, rime, and mixed icing are found in layers with below-freezing (negative) temperatures and super-cooled water droplets. Users should be aware that official forecast freezing-level information is specified within the AIRMET Zulu Bulletins (CONUS and Hawaii) and the AIRMET “ICE AND FZLVL” information embedded within the FAs (Alaska only).
11/14/16 Aviation Weather Services AC 00-45H 5-102 Figure 5-44. Aviationweather.gov Freezing Level Graphic—Example
5.15 Upper-Air Forecasts.
NWP models, run on super computers, generate surface and upper-air forecasts, known as “Model Guidance” to meteorologists. The NWS NCO runs several models daily and produces hundreds of surface and upper-air guidance products, valid from model run time
(i.e., 00-hour) out to several days or weeks (e.g., 340 hours after model run time) depending on the model. Their Web site, Model Analyses and Guidance (see Figure 5-45, NWS NCEP Central Operations Model Analyses and Guidance Web Site), contains a user’s guide as well as a product description link that provides details on the various products.
11/14/16 Aviation Weather Services AC 00-45H Figure 5-45. NWS NCEP Central Operations Model Analyses and Guidance Web Site DOC NOAA NWS NCEP Centers: AWC CPC EMC NCO NHC OPC SPC SWPC WPC NCEP Home ≥ NOO Home ≥ Systems Integration Branch ≥ Model Analyses and Guidance Model Analyses and Guidance Information + Website Check here for the Latest News Select Model Guidance, Observations and Analyses, or Tropical Guidance
MODEL GUIDANCE OBSERVATIONS AND ANALYSES TROPICAL GUIDANCE Upcoming Changes | User's Guide | Frequently Asked Questions | Product Description Document MAG V3.0.0 NOAA/ National Weather Service Disclaimer Privacy Policy National Centers for Environmental Prediction Credits About Us 5830 University Research Court Glossary Career Opportunities College Park, MD 20740 NCEP Internet Services Team Page last modified: May 20 2013 17:08 PM UTC.
A user's guide, located within Web site Information (upper right corner), provides descriptions, details, and examples of the various products.
5.15.1 Constant Pressure Levels Forecasts.
Constant pressure level forecasts (see Figure 5-46, 300 MB Constant Pressure Forecast-Example) are just one of the many products produced by NWP models.
Constant pressure level forecasts are the computer model's depiction of select weather
(e.g., wind) at a specified constant pressure level (e.g., 300 MB), along with the altitudes (in meters) of the specified constant pressure level. Constant pressure level forecasts when considered together describe the three-dimensional aspect of pressure systems.
Each product provides a plan-projection view of a specified pressure altitude at a given forecast time.
5-103