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.
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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.
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5.15.1.2.4 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 1st 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 5-20, Wind and Temperature Aloft Forecast Decoding Examples, shows data for MKC (Kansas City, MO).
5-113 Table 5-20. 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
5.15.1.3 Use.
Table 5-21, Wind and Temperature Aloft Forecast (FB) Periods, provides the time periods for use of FB Wind and Temperature forecasts.
Table 5-21. Wind and Temperature Aloft Forecast (FB) Periods Model Run Product Available 6 hour Forecast Valid For Use 12 hour Forecast Valid For Use 24 hour Forecast 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
5.16 Freezing-Level Graphics.
The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0 °C. This altitude is also known as the height of the 0 °C constant-temperature surface. A freezing-level graphic (see Figure 5-52, Aviationweather.gov Freezing Level Graphic—Exampl e) shows the height of the 0 °C constant-temperature surface.
5-114 The concept of freezing level becomes slightly more complicated when more than one altitude is determined to be at a temperature of 0 °C. 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 website.
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.
5.16.1 Issuance.
The initial analysis and forecast graphics are updated hourly.
5.16.2 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.
5.16.3 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 supercooled 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).
5-115 Figure 5-52. Aviationweather.gov Freezing Level Graphic—Example
5.17 Uppe r-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 website, Model Analyses and Guidance (see Figure 5-53, NWS NCEP Central Operations Model Analyses and Guidance Website), contains a user ’s guide as well as a product description link that provides details on the various products.
Figure 5-53. NWS NCEP Central Operations Model Analyses and Guidance Website DOC NOAA NWS NCEP Centers: AWC CPC EMC NCO NHC OPC SPC SWPC WPC NCEP Home ≥ NCO 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 ·3.0.0 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 website Information (upper right corner), provides descriptions, details, and examples of the various products.
5.17.1 Constant Pressure Levels Forecasts.
Constant pressure level forecasts (see Figure 5-54, 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.
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5-117 Figure 5-54. 300 MB Constant Pressure Forecast—Example
Contours of the height of the 300 MB surface are presented as solid lines. Windbarbs are used to show the direction and speed of the wind. Shading is done for wind speeds greater than 70 kts or greater and generally represents the jet stream. In this example, the jet s tream extends from Alaska to Southern California to New England.
5.17.1.1 Issuance.
Constant pressure level forecasts are produced several times a day depending on the model. NCEP’s Global Forecast System (GFS) model and North American Model (NAM) model produce forecasts four times per day, with initial times of 00, 06, 12, and 18 UTC. Other higher resolution models such as the High Resolution Rapid Refresh (HRRR) produce forecasts at hourly intervals.
5.17.1.2 Content.
Constant pressure level forecasts vary in content depending on the selected model and product. Most provide a wind forecast that may be combined with either temperature, relative humidity, or certain derived parameters
(e.g., vorticity).
Many consta nt pressure levels are available for display depending on the model. For example, the NCEP’s Model Analyses and Guidance website (see Figure 5-53) provides displays of NCEP’s GFS model constant pressure levels contained in Table 5-22, Select Constant Pressure Levels From the GFS Model. It should be noted that the levels provided on the website are
5-118 only a subset of the levels available from the model that are routinely made available to NWS meteorologists and others (e.g., 400 millibars (mb), 600 mb).
Table 5-22. Select Constant Pressure Levels From the GFS Model Constant Pressure Level Approximate Altitude (MSL) 925 MB 2,500 850 MB 5,000 700 MB 10,000 500 MB 18,000 300 MB 30,000 250 MB 34,000 200 MB 39,000
5.17.1.3 Use.
Constant pressure level forecasts are used to provide an overview of weather patterns at specified times and pressure altitudes and are the source for wind and temperature aloft forecasts.
Pressure patterns cause and characterize much of the weather. Typically, lows and troughs are associated with clouds and precipitation while highs and ridges are associated with fair weather, except in winter when valley fog may occur. The location and strength of the jet stream can be viewed at 300 MB, 250 MB, and 200 MB levels.
5.18 Short-Range Surf ace Prognostic (Prog) Charts.
The NWS’s WPC provides Short-Range Surface Prognostic (Prog) Charts (see Figure 5-55, NDFD Surface Prog Forecast—Example) of surface pressure systems, fronts, and precipitation for a 2½-day period. The forecast area covers the CONUS, the coastal waters. The forecasted conditions are divided into five forecast periods: 12, 18, 24, 48, and 60 hours. Each chart depicts a “snapshot” of weather elements expected at the specified valid time.
The Short-Range Surface Prognostic (Prog) Charts combine WPC forecasts of fronts, isobars, and high/low pressure systems with the NWS’s National Digital Forecast Database (NDFD) digital forecasts from NWS WFO.
The Sur face Prognostic (Prog) Charts are available at https://www.aviationweather.gov.
5-119 Figure 5-55. NDFD Surface Prog Forecast—Example
5.18.1 Content.
5.18.1.1 Precipitation.
The Short-Range Surface Prog Forecast provides precipitation forecasts in the following depiction:
• NDFD Rain (Chance)–(light green)–There is a 25 to less than 55 percent probability of measurable rain (≥0.01”) at the valid time.
• NDFD Rain (Likely)–(dark green)–There is a greater than or equal to 55 percent probability for measurable rain (≥0.01”) at the valid time.
• NDFD Snow (Chance)–(light blue)–There is a 25 to less than 55 percent probability of measurable snowfall (≥0.01” liquid equivalent) at the valid time.
• NDFD Snow (likely)–(dark blue)–There is a greater than or equal to 55 percent probability of measurable snow (≥0.01” liquid equivalent) at the valid time.
• NDFD Mix (Chance)–(light purple)–There is a 25 to less than 55 percent probability of measurable mixed precipitation (≥0.01” liquid equivalent) at
5-120 the valid time. “Mixed” can refer to precipitation where a combination of rain and snow, rain and sleet, or snow and sleet are forecast.
• NDFD Mix (Likely)–(dark purple)–There is a greater than or equal to 55 percent probability of measurable mixed precipitation (≥0.01” liquid equivalent) at the valid time. “Mixed” can refer to precipitation where a combination of rain and snow, rain and sleet, or snow and sleet are forecast.
• NDFD Ice (Chance)–(light brown)–There is a 25 to less than 55 percent probability of measurable freezing rain (≥0.01”) at the valid time.
• NDFD Ice (Likely)–(brown)–There is a greater than or equal to 55 percent probability of measurable freezing rain (≥0.01”) at the valid time.
• NDFD T-Storm (Chance)–(red hatching)–There is a 25 to less than 55 percent probability of thunderstorms at the valid time. Areas are displayed with diagonal red hatching enclosed in red border.
• NDFD T-Storm (Likely and/or Severe)–(dark red)–There is a greater than or equal to 55 percent probability of thunderstorms and/or the potential exists for some storms to reach severe levels at the valid time.
5.18.1.2 Symbols.
Figure 5-56. Surface Prog Forecast Symbols
5.18.1.3 P ressure Systems.
Pressure systems are depicted by pressure centers, troughs, isobars, drylines, tropical waves, tropical storms, and hurricanes using standard symbols (see Figure 5-56, Surface Prog Forecast Symbols). Isobars are denoted by solid thin black lines and labeled with the appropriate pressure in millibars.
The central pressure is plotted near the respective pressure center.