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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.
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5.18.1.4 Fronts.
Fr onts are depicted using the standard symbols in Figure 5-56.
5.18.1.5 Squall Lines.
Squall lines are denoted using the standard symbol in Figure 5-56.
5.18.2 Issuance.
The Short-Range Surface Prognostic (Prog) Forecasts are issued by the WPC in College Park, MD. Table 5-23, Short-Range Surface Prog Forecast Schedule, provides the product schedule. The 12- and 24-Hour Surface Prognostic (Prog). They are available on the WPC website.
Table 5-23. Short-Range Surface Prog Forecast Schedule Product Issuance Times (UTC) 6 and 12 hour forecasts 0200 and 1400 18 and 24 hour forecasts 0430 and 1630 30, 36 and 48 hour forecasts 0730 and 1930 60 hour forecast 0900 and 2100
5.18.3 Use.
Short-Range Surface Prognostic (Prog) Forecasts can be used to obtain an overview of the progression of surface weather features during the next 2½-days hours. The progression of weather is the change in position, size, and intensity of weather with time.
5.19 Significant Weather (SIGWX) Forecast.
Note: Significant Weather Forecasts may be depicted in monochrome or color display.
The colors used for symbols and as well as the color and style of lines is not standard.
The colors of jet streams, turbulence, cloud cover, and other elements may vary depending on the website and service provider. The examples shown in this paragraph are from the NWS AWC’s and AAWU’s Web pages. Users of Significant Weather Forecasts should always refer to any legend or Help Page or user information on the website for details on the content and display of the weather information.
5.19.1 Low-Level Significant Weather (SIGWX) Charts.
The Low-Level Significant Weather (SIGWX) Charts (see Figure 5-57, 12-Hour Low-Level SIGWX Chart—Exam ple) provide a forecast of aviation weather hazards primarily intended to be used as guidance products for pre-flight briefings. The forecast domain covers the CONUS and the coastal waters for altitudes FL240 and below. Each depicts a “snapshot” of weather expected at the specified valid time.
5-122 Figure 5-57. 12-Hour Low-Level SIGWX Chart—Example
5.19.1.1 Co ntent.
Low-Level SIGWX Charts depict weather flying categories, turbulence, and freezing levels (see Figure 5-58, Low-Level SIGWX Chart Symbols). In flight icing is not depicted on the Low-Lev el SIGWX Chart.
Depending on the website or service provider, the Low-Level SIGWX Charts may be combined with Surface Prognostic (PROG) Charts to create a four-panel presentation. For example, the left two panels represents the 12-hour forecast interval and the right two panels the 24-hour forecast interval. The upper two panels depict the SIGWX Charts and the lower two panels the Surface Prog.
Figure 5-58. Low-Level SIGWX Chart Symbols Flight planning only. See TAFs for specific terminal forecast celling less than Luuu tt andror visibility less than 3 miles ceiling 1000-3000 ft inclusive andior visibility 3-5 miles incl moderate or greater turbulence freezing level above mean sea level freezing level at surface TStorms imply possible svr or greater turb, svr icing and LLWS.
MODERATE TURBULENCE TOP (Hundreds of feet MSL) SEVERE TURBULENCE 240/100 Base (Hundreds of feet MSL)
EXTREME TURBULENCE Note: The colors used in the Low-Level Significant Weather Charts may vary depending on the website or service provider.
5.19.1.1.1 Flying Categories.
IFR areas are outlined with a solid red line, marginal VFR (MVFR) areas are outlined with a scalloped blue line, and VFR areas are not depicted (see Figure 5-59, Low-Level SIGWX Chart Flying Categories-Example).
Figure 5-59. Low-Level SIGWX Chart Flying Categories-Example 5-123