5-129 Table 5-26. Mid-Level SIGWX Chart Issuance Schedule Issued (UTC) Valid (UTC) 0800 0000 (next day) 1400 0600 (next day) 2000 1200 (next day) 0200 1800
5.19.2.3 Use.
The Mid-Level SIGWX Chart is used to determine an overview of selected flying weather conditions between 10,000 ft MSL and FL450. It can be used by airline dispatchers for flight planning and weather briefings before departure and by flightcrew members during flight.
5.19.3 High-Level Significant Weather (SIGWX) Charts.
High-Level SIGWX Charts (see Figure 5-64, High-Level SIGWX Chart—Example) provide a forecast of significant en route w eather phenomena over a range of flight levels from FL250 to FL630. Each chart depicts a “snapshot” of weather expected at the specified valid time. They are available on https://www.aviationweather.gov.
Figure 5-64. High-Level SIGW Chart-Example
ISSUED BY WAFC WASHINGTON VALID O50 A SIG N 2009 _ OR TURE 270 300 270 TERED 80/470 390 ฿16799 1390
- 400 450 "PATRICIA 530 500] 500 500 500 480 450 390 390 340 300 1390 340 [270] 200 390 300 5-130
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5.19.3.1 Content.
5.19.3.1.1 Thunderstorms and Cumulonimbus Clouds.
The abbreviation CB is only included where it refers to the expected occurrence of an area of widespread cumulonimbus clouds, cumulonimbus along a line with little or no space between individual clouds, cumulonimbus embedded in cloud layers, or cumulonimbus concealed by haze. It does not refer to isolated cumulonimbus not embedded in cloud layers or concealed by haze.
Each cumulonimbus area is identified with CB and characterized by coverage, bases, and tops.
Coverage is identified as isolated (ISOL) meaning less than 4/8th, occasional (OCNL) meaning 4/8th to 6/8th, and frequent (FRQ) meaning more than 6/8th coverage. Isolated CBs can only be depicted when they are embedded (EMBD) in clouds or concealed by haze. Occasional CBs can be depicted with or without embedded (EMBD).
The vertical extent of cumulonimbus layer is specified by top and base heights. Bases that extend below FL250 (the lowest altitude limit of the chart) are encoded XXX.
CBs are depicted by enclosed (red) scalloped lines. The identification and characterization of each CB area will appear within or adjacent to the outlined area. If the identification and characterization is adjacent to an outlined area, an arrow will point to the associated cumulonimbus area.
On significant weather charts, the inclusion of CB shall be understood to include all weather phenomena normally associated with cumulonimbus
(i.e., thunderstorm, moderate or severe icing, moderate or severe turbulence, and hail).
5.19.3.1.2 Moderate or Severe Turbulence.
Forecast areas of moderate or severe turbulence (see Figure 5-65, High-Level SIGWX Chart Turbulence—Examples ) associated with windshear zones and/or mountain waves are enclosed by bold yellow dashed lines. Intensities are identified by standard symbols (see Table 5-25).
The vertical extent of turbulence layers is specified by top and base heights, separated by a horizontal line. Turbulence bases that extend below FL250 are identified with XXX.
Convective or thunderstorm turbulence is not identified.
5-132 Figure 5-65. High-Level SIGWX Chart Turbulence—Examples
5.19.3.1.3 Moderate or Severe Icing.
Moderate and severe icing (outside of thunderstorms) above FL240 is rare and is not generally forecasted on High-Level SIGWX charts.
5.19.3.1.4 Jet Streams.
A jet stream axis with a wind speed of more than 80 kts is identified by a bold (green) line. An arrowhead is used to indicate wind direction. Wind change bars (double-hatched, light green lines) positioned along a jet stream axis identifies 20-knot wind speed changes (see Figure 5-66, High-Level SIGWX Chart Jet Stream—E xample).
Symbols and altitudes are used to further characterize a jet stream axis. A standard wind symbol (light green) is placed at each pertinent position to identify wind velocity. The flight level is placed adjacent to each wind symbol to identify the altitude of the jet stream core or axis.
Jet stream vertical depth forecasts are included when the maximum speed is 120 kts or more. Jet depth is defined as the vertical depths to the 80-knot wind field above and below the jet stream axis using flight levels. Jet depth information is placed at the maximum speed point only, normally at one point on each jet stream. When the jet stream is very long and there are several wind maxima, then each maximum should include forecasts of the vertical depth.
5-133 Figure 5-66. High-Level SIGWX Chart Jet Stream—Example
Forecast maximum speeds of 100 kts at FL310 at one location and 120 kts at FL290 at another location. At the latter location, the base of the 80-knot wind field it FL210, and the top of the 80-knot wind field is FL340.
5.19.3.1.5 Tropopause Heights.
Tropopause heights are plotted at selected locations on the chart. They are enclosed by rectangles and plotted in hundreds of feet MSL (see Figure 5-67, High-Level SIGWX Chart Tropopause Height—Examples). Centers of high (H) and low (L) tropopause heights are enclosed by polygons and plotted in hundreds of feet MSL.
Figure 5-67. High-Level SIGWX Chart Tropopause Height—Examples
5.19.3.1.6 Tropical Cyclones.
Tropical cyclones, i.e., with surface wind speed 34 kts or greater, are depicted by the symbol depicted in Figure 5-68, High-Level SIGWX Chart Tropical Cyclone—Examples, with the storm’s name positioned adjacent to the sym bol. Cumulonimbus clouds meeting chart criteria are identified and characterized relative to each storm.
5-134 Figure 5-68. High-Level SIGWX Chart Tropical Cyclone—Examples
5.19.3.1.7 Volcanic Eruption Sites.
Volcanic eruption sites are identified by a trapezoidal symbol depicted in Figure 5-69, High-Level SIGWX Chart Volcanic Eruption Site—Example.
The dot on the base of the trapezoid identifies the location of the volcano. The name of the volcano, its latitude, and its longitude are noted adjacent to the symbol.
Figure 5-69. High-Level SIGWX Chart Volcanic Eruption Site—Example
5.19.3.1.8 W idespread Sandstorms and Duststorms.
Widespread sandstorms and duststorms are labeled with the symbol depicted in Figure 5-70, High-Level SIGWX Chart Widespread Sandstorm and Duststorm—Example. The vertical extent of sand or dust is specified by top and base heights, separated by a horizontal line. Sand or dust that extends below the lower limit of the chart (FL250) is identified with XXX.
Figure 5-70. High-Level SIGWX Chart Widespread Sandstorm and Duststorm—Example
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5.19.3.2 Issuance.
In accordance with the WAFS of the ICAO, High-Level SIGWX forecasts are provided for the en route portion of international flights.
High-Level SIG WX forecasts are issued as a global data set in digital format by two WAFCs, one at NWS’s AWC and the other at the United Kingdom’s Meteorological Office. Each center produces a global data set of significant weather that is then made available (displayed) in chart form for different areas of the globe. These charts are available on https://www.aviationweather.gov.
Corrections are issued for format errors or missing information. These charts are not amended.
Table 5-27. High-Level SIGWX FORECAST Issuance Schedule Issued (UTC) Valid (UTC) 0800 0000 (next day) 1400 0600 (next day) 2000 1200 (next day) 0200 1800
5.19.3.3 Use.
High-Level SIGWX forecasts are provided for the en route portion of international flights. These products are used directly by airline dispatchers for flight planning and weather briefings before departure and by flightcrew members during flight.
5.19.4 Alaska Significant Weather (SIGWX) Charts.
The Alaska SIGWX charts (see Figure 5-71, Alaska Significant Weather Chart— Example) are a series of four forecasts (24-hour, 36- hour, 48-hour, and 60-hour) valid at specified times. These charts provide a graphical overview of the specified forecast weather primarily for lower flight altitudes.
5.19.4.1 Issuance.
The AAWU issues the Alaska SIGWX charts. These charts are issued twice a day at 0530 and 1330 UTC during Alaska Standard Time, and 0430 and 1230 UTC during Alaska Daylight Time. The 1330/1230 UTC-issued 24-hour SIGWX chart may be updated around 2145/2045 UTC valid at 1200 UTC the next day.
5-136 Figure 5-71. Alaska Significant Weather Chart—Example
5.19.4.2 C ontent.
5.19.4.2.1 Surface Pressure Systems and Fronts.
Pressure systems and fronts are depicted using standard 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.
5.19.4.2.2 Areas of IFR and MVFR Weather Conditions.
Areas of forecast IFR and MVFR conditions are shown in red and blue hatching, respectively.
5.19.4.2.3 Freezing Levels.
Forecast freezing levels are depicted for the surface (dashed red line) and at 2,000-foot intervals (dashed green lines).
Note: Areas of in-flight icing forecasts are not included in the Alaska SIGWX forecasts.
5.19.4.2.4 Low-Level Turbulence.
Areas of forecast moderate or greater Non-Convective low-level turbulence are depicted with black dots. Turbulence altitudes are not included but can be
5-137 considered as turbulence that is near the surface as a result of wind interactions with the terrain. In most cases, it would be within 6,000 ft above the terrain.
5.19.4.2.5 Thunderstorms.
Areas of forecast thunderstorms are depicted with red dots. Thunderstorm areal coverage, cloud bases, and tops are not included.
5.19.4.2.6 Use.
These charts provide a graphical overview of the specified forecast weather primarily for lower flight altitudes.
5.20 World Area Forecast System (WAFS).
ICAO’s WAFS supplies aviation users with global aeronautical meteorological en route forecasts suitable for use in flight-planning systems and flight documentation.
Two WAFCs, WAFC Washington and WAFC London, have the responsibility to issue the WAFS forecasts. WAFC Washington is operated by the NWS’s NCO in College Park, MD, and the AWC in Kansas City, MO. WAFC London is operated by the United Kingdom’s Meteorological Office in Exeter, United Kingdom.
5.20.1 WAFS Forecasts.
Both WAFC Washington and WAFC London issue the following WAFS forecasts in accordance with ICAO Annex 3, Meteorological Service for International Air Navigation.
• Global forecasts of:
o Upper wind and temperature (i.e., wind and temperature aloft, which is also issued in chart form for select areas);
o Upper-air humidity;
o Geopotential altitude of flight levels;
o Flight level and temperature of tropopause (i.e., tropopause forecast);
o Direction, speed, and flight level of maximum wind;
o Cumulonimbus clouds;
o Icing; and o Turbulence.
• Global foreca sts of Significant Weather (SIGWX), i.e., High-Level Significant Weather (SIGWX) forecasts (see paragraph 5.19.3).
• Select regional areas of Medium-Level Significant Weather (SIGWX) forecasts (see paragraph 5.19.2).
Note: See paragraphs 5.19.2 and 5.19.2.1 for details on the WAFS High-Level and Medium-Level SIG WX forecasts.
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5.20.1.1 Issuance.
The WAFS forecasts of upper wind, temperature, and humidity; direction, speed, and flight level of maximum wind; flight level and temperature of tropopause; areas of cumulonimbus clouds; icing; turbulence; and geopotential altitude of flight levels are issued four times a day by both WAFC Washington and WAFC London.
These forecasts are produced from weather computer models and are not modified by WAFC forecasters. WAFC Washington’s is from the GFS model.
These forecasts are issued in grid-point format, i.e., WMO GRIB2 format.
The grid-point horizontal resolution for the WAFS forecast is 1.25 degree latitude by 1.25 degree longitude. This is equivalent to a 75 x 75 NM grid box at the equator with the grid boxes becoming progressively smaller toward the poles.
These forecasts are valid for fixed valid times at 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, and 36 hours after the time (0000, 0600, 1200, and 1800 UTC) on which the forecasts were based.
5.20.1.2 WAFS Wind and Temperature.
Wind and temperature forecasts are issued for flight levels (FL) 050 (850 MB), 100 (700 MB), 140 (600 MB), 180 (500 MB), 240 (400 MB), 270 (350 MB), 300 (300 MB), 320 (275 MB), 340 (250 MB), 360 (225 MB), 390 (200 MB), 410 (175 MB), 450 (150 MB) and 530 (100 MB).
Note: ICAO uses flight levels below 18,000 MSL for global weather products.
WAFC wind and temperature forecasts use a plotting model where the air temperature (degrees Celsius) is the center of the data point and the wind direction and speed follows the standard model (see Figure 5-72, WAFS Wind and Temperature 6-Hour Forecast at FL390—Example) with the exception that wind speed for points in the Southern Hemisphere is flipped. Note the data points do not correspond to any airports or reference points with names or identifiers.
WAFS global wind and temperature forecasts are provided in grid point format (e.g., computer format) for use in flight-planning systems. Chart format is also provided on the AWC’s Web page (under “Flight Folder”).
Figure 5-72. WAFS Wind and Temperature 6-Hour Forecast at FL390—Example PWNB20 WORLD AREA FORECAST CENTER WASHINGTON A 694 -70 FL 390 WINDS/TEMPERATURES OOUTC MAR MAR 31 312 2015
HIND SPEEDUNLESS POSITIVES UNSIGNED 145914601 60N 60N 60N + 584-544-531 541-97458 4 95 99 49-50 GOW 40W gs 13810561 5 50N W62 4L60 9 59 85 57-60 61 61-60 474998535861164 65 62 40N se s" 51 38 60 50 9o 6,26 565556 15961 62 64 ''5911-604-60 61 30N 3ON 59 60 616015 458 157 * 55 11 52 2ON 55 5611-58 51 52483 55 85 55 A 20N ' 83"59 848-85-89183 51 51 1-51-52 54 kU54|56 A:-55 4!
10N 10N ' 2'52 52'52 8353-8352 A251 4 52 4l1:52 All 52 A53 A53 AlL53 4 4524 524 524 834831 82182152,5 535355353 52-32/83 53m 531154+54r 545-55755 54 11 51177-527-53 5555 205 99 99 387-82-86 56 55 1 50525453 54177-5455 30S 555-567758 11521 53977753 1 " 52 mistr 52 17-55 07 57 1 58 40S 52 5 83 51 99 49 rr 52 r551/58 771555-568 59-61 2 1 4987-4787-461 477 50S "33160~60W 150 190132 204 95 801-42 1757 5-139
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5.20.1.3 Humidity, Maximum Wind, Tropopause Forecasts.
No specific charts are issued for global upper-air humidity, maximum wind, height of tropopause, and altitude of flight levels. These products are provided in grid point format (e.g., computer format) for use in flight-planning systems.
Data from these forecasts are used by the WAFC forecasters to produce the High-Level and Medium-Level SIGWX forecasts, which contain tropopause and jet stream forecasts.
Humidity data is produced for FLs 50 (850 MB), 100 (700 MB), 140 (600 MB), and 180 (500 MB).
5.20.1.4 WAFS Tur bulence, Icing, and Cumulonimbus Cloud Forecasts.
WAFS global turbulence, icing, and cumulonimbus cloud forecasts are provided in grid point format (e.g., computer format) for use in flight-planning systems, but the AWC does make these available on their website in Web display format and not chart format. The Web display allows the user to select various products and flight levels and view the forecasts as single time steps or in a movie loop sequence. More detailed information is provided on https://www.aviationweather.gov under WAFS Forecasts.
The WAFS global turbulence, icing, and cumulonimbus cloud forecasts are actually a blend of the WAFC Washington global turbulence, icing, and cumulonimbus cloud forecasts and the WAFC London global turbulence, icing, and cumulonimbus cloud forecasts. In other words, each WAFC produces their own global turbulence, icing, and cumulonimbus cloud forecasts using their own global computer models (WAFC Washington uses NCEP’s GFS model). The two WAFC’s forecasts, for turbulence, icing, and cumulonimbus cloud only, are then merged together to eliminate any differences between the two sets of forecasts.
WAFC s provide written guidance material on these WAFS forecasts, available on ICAO’s Meteorology Web page. Consult the Guidance on the Harmonized WAFS Grids for Cumulonimbus Cloud, Icing and Turbulence Forecasts - 11 September 2012 at http://www.icao.int/safety/meteorology/WA FSOPSG/Pages/GuidanceMaterial.aspx.
5.20.1.4.1 WAFS Turbulence.
Two kinds of turbulence forecasts are provided: Clear Air Turbulence (CAT) and in-cloud turbulence.
Clear Air Turbulence.
As of 2015, WAFS CAT forecasts are derived from an algorithm that is based on the Ellrod Index. The Ellrod Index results from an objective technique for forecasting CAT. The index is calculated based on the product of horizontal deformation and vertical windshear derived from numerical model forecast winds aloft. Future upgrades to this product are planned, which may include