Chapter 27, Forecasts 27-28
• Turbulence Forecast, and
• Convective Outlook (seasonal product and only issued from May 1 through September 30).
Additional products may be available. Some of these may be labeled experimental ; thus, the contents and
format are subject to change.
27.7.1 AAWU Flying Weather
The Flying Weather graphic (see Figure 27-4) includes flying weather conditions and any active volcanoes
in Alaska. This product consists of two six-hour forecasts valid for a total of 12 hours. Each forecast
specifies where such conditions can be expected within the six-hour valid time.
Areas of occasional or continuous MVFR/IFR are represented by shaded regions (red for IFR, blue for
MVFR), whereas areas of predominately VFR weather are not shaded. MVFR/IFR conditions are possible
outside these shaded regions, but only isolated in coverage. Strong surface winds are shown in a circle hatch
overlay. Active volcanoes are denoted by a volcano symbol at the location of the volcano.
Note: This forecast is also referred to as the “IFR/MVFR” graphic on their website.
Figure 27-4. Alaska Flying Weather Example
27.7.2 Alaska Surface Forecast
The Surface Forecast graphic ( see Figure 27-5) illustrates prominent surface features, including sea level
pressure, areas of high and low pressure, fronts and troughs, and precipitation. Each forecast shows the
surface weather that can be expected within one hour of the designated time.
Areas of high pressure are depicted along with the maximum sea level pressure. Areas of low pressure are
depicted with the minimum sea level pressure. The mean 12 -hour motion of lo w-pressure systems is also
Chapter 27, Forecasts 27-29
shown. Areas of occasional or continuous precipitation and/or fog are represented by shaded regions (green
for precipitation, yellow for fog), whereas isolated or scattered precipitation is not shaded. This product is
issued every six hours with forecasts valid for 00Z, 06Z, 12Z, and 18Z.
Figure 27-5. Alaska Surface Forecast Example
27.7.3 Alaska Icing Forecast
The Icing Forecast graphic ( see Figure 27-6) provides information about freezing levels and the potential
for significant icing at specified valid times.
Freezing level heights are blue-filled contours (every 2,000 ft). Areas of isolated (ISOL) moderate (MOD)
icing are shaded yellow, areas of occasional (OCNL) or continuous ( CONS) moderate icing are shaded
orange, and red is used for moderate with isolated severe (SEV) icing (refer to SIGMETs for occasional or
greater severe icing). These forecasts are issued every eight hours and amended as needed.
Chapter 27, Forecasts 27-30
Figure 27-6. Alaska Icing Forecast Example
27.7.4 Alaska Turbulence Forecast
The Turbulence Forecast graphic (see Figure 27-7) depicts areas of significant turbulence at specified valid
times.
Areas of isolated (ISOL) moderate (MOD) turbulence are shaded yellow, areas of occasional (OCNL) or
continuous (CONS) moderate turbulence are shaded orange, and red is used for moderate with isolated
severe (SEV) turbulence (refer to SIGMETs for occasional or greater severe turbulence).
Separate graphics are provided for low-level (defined for this product as FL180 and below) and high-level
(defined for this product as above FL180) turbulence.
Chapter 27, Forecasts 27-31
Figure 27-7. Alaska Turbulence Forecast Example
27.7.5 Alaska Convective Outlook
The Convective Outlook graphic ( see Figure 27-8) is a seasonal product that provides information about
convective activity at specific valid times. Each forecast indicates where conditions are favorable for the
development of towering cumulus and thunderstorms.
Locations of towering cumulus are depicted in yellow. Locations of isolated (ISOL), scattered (SCT), and
widespread (WDSPRD) thunderstorms (TS) are depicted in orange, red, and dark red, respectively. Cloud
bases and tops are also depicted.
Chapter 27, Forecasts 27-32
Figure 27-8. Alaska Convective Outlook
27.8 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 NCO in College Park, MD , and the NWS AWC in Kansas
City, MO. WAFC London is operated by the United Kingdom ’s Meteorological Office in Exeter, United
Kingdom.
27.8.1 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 FLs;
o FL and temperature of tropopause (i.e., tropopause forecast);
o Direction, speed, and FL of maximum wind;
Chapter 27, Forecasts 27-33
o Cumulonimbus clouds;
o Icing; and
o Turbulence.
• Global forecasts of SIGWX (i.e., High-Level SIGWX forecasts) (see Section 27.9.3).
• Select regional areas of Mid-Level SIGWX forecasts (see Section 27.9.2).
27.8.1.1 Issuance
The WAFS forecasts of upper wind, temperature, and humidity; direction, speed, and FL of maximum
wind; FL and temperature of tropopause; areas of cumulonimbus clouds; icing; turbulence; and geopotential
altitude of FLs 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 forecast is from the Global Forecast System (GFS) model. These forecasts are issued
in grid-point format (i.e., WMO Gridded Binary, Edition 2 (GRIB2) format).
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. Additional valid times are
planned to be implemented in 2024.
27.8.1.2 WAFS Wind and Temperature Forecasts
Wind and temperature forecasts are issued for FL s 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 FLs 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 27-9)
with the exception that wind speed for points in the Southern Hemisphere is flipped. Note that 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 website.
Chapter 27, Forecasts 27-34
Figure 27-9. WAFS Wind and Temperature Six-Hour Forecast at FL390—Example
Chapter 27, Forecasts 27-35
27.8.1.3 Humidity, Maximum Wind, and Tropopause Forecasts
No specific charts are issued for global upper air humidity, maximum wind, height of tropopause, and
altitude of FLs. These products are provided in grid point format (e.g., com puter 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). Additional
valid times are planned to be implemented in 2024.
27.8.1.4 WAFS Turbulence, Icing, and Cumulonimbus Cloud Forecasts
WAFS global turbulence, icing, and cumulonimbus cloud forecasts are provi ded 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 FLs and view the forecasts as single time steps or in a movie -loop sequence. More detailed
information is provided on the AWC’s website.
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 ot her words, each WAFC produces their own
global turbulence, icing, and cumulonimbus cloud forecasts using their own global computer models
(WAFC Washington uses the NCEP’s GFS model). The two WAFCs’ forecasts, for turbulence, icing, and
cumulonimbus cloud only, are then merged together to eliminate any differences between the two sets of
forecasts.
27.9 Significant Weather (SIGWX)
SIGWX forecasts may be depicted in monochrome or color display. The colors used for symbols as well
as the color and style of lines are 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 section are
from the NWS AWC’s and the AAWU’s websites. Refer to any legend, Help Page, or user information on
the websites for details on the content and display of the weather information.
27.9.1 Low-Level Significant Weather (SIGWX) Charts
The Low -Level SIGWX Charts (see Figure 27-10) provide an overview of selected aviation weather
hazards up to FL240 at 12 and 24 hours into the future.
The forecast domain covers the CONUS and the coastal waters. Each depicts a “snapshot” of weather
expected at the specified valid time.
Chapter 27, Forecasts 27-36
Figure 27-10. 12-Hour Low-Level SIGWX Chart—Example
27.9.1.1 Issuance
Low-Level SIGWX Charts are issued four times per day by the NWS AWC (see Table 27-10). Two charts
are issued: a 12-hour and a 24-hour prognostic (prog) chart.
Table 27-10. Low-Level SIGWX Chart Issuance Schedule
Issuance Time
~1720Z ~2310Z ~0530Z ~0935Z
Chart Valid Time
12-Hour Prog 00Z 06Z 12Z 18Z
24-Hour Prog 12Z 18Z 00Z 06Z
27.9.1.2 Content
Low-Level SIGWX Charts depict weather flying categories, turbulence, and freezing levels (see Figure
27-11). In-flight icing is not depicted on the Low-Level SIGWX Chart.
Depending on the website or service provider, the Low -Level SIGWX Charts may be combined with
Surface Prog Charts to create a four -panel presentation. For example, the l eft two panels represent the
12-hour forecast interval and the right two panels represent the 24-hour forecast interval. The upper two
panels depict the SIGWX Charts and the lower two panels the Surface Prog.