Chapter 28, Aviation Weather Tools 28-1
28 Aviation Weather Tools
28.1 Introduction
The fifth of five types of aviation weather information discussed in this handbook is aviation weather tools.
Aviation weather tools are web-based applications that incorporate multiple weather products into a
web-based interactive display.
This c hapter will describe three web -based interactive displays : the GFA Tool, the Flight Service ’s
Interactive Map , and the GFA-LA (Graphical Forecasts for Aviation – Low Altitude previously called
Helicopter Emergency Medical Services HEMS) Tool.
This chapter describes these web -based displays as they are configured in 20 22. Enhancements to these
displays will likely occur in the coming years as technology improves. Users will find information on any
enhancements on the providers’ websites.
Chapter 28, Aviation Weather Tools 28-2
28.2 Graphical Forecasts for Aviation (GFA) Tool
The GFA Tool is a set of web-based displays intended to provide the necessary aviation weather information
to give users a complete picture of the weather that may impact their flight operations. It is a one-stop shop
for multiple data fields. The AWC website includes observational data, forecasts, and advisories including
thunderstorms, clouds, flight category, precipitation, icing, turbulence , and wind. Hourly model data and
forecasts, including information on clouds, flight category, precipitation, icing , turbulence, wind, and
graphical output from the NWS’ NDFD, are available. Built with modern geospatial information tools,
users can pan and zoom to focus on areas of greatest interest.
Descriptions of the observations, forecasts , and advisories that are used in the GFA Tool have been
presented in other chapters within this handbook. This section does not show or describe the many possible
overlays for the GFA Tool, since the AWC has produced a very thorough and complete description under
the “Info” tab on the AWC’s GFA Tool website, which also includes a tutorial video. In addition, the
GFA Tool will continue to be enhanced; therefore, users will be assured of being informed of the latest
GFA Tool information by referring to the “Info” tab on AWC’s GFA Tool website. In fact, a significant
change was made in late 2023 when the Helicopter Emergency Medical Services (HEMS) tool was moved
into the GFA and is now the GFA Low Altitude (GFA -LA). This Low Altitude mode focuses on altitudes
up to 5,000 ft AGL. Overlays include roads, NAVAIDs, airports, and heliports for the entire United States.
More detail is revealed as you zoom in, and individual layers can be turned on or off independently.
Additional information, including a tutorial, can be found on the AWC’s website.
Caution should be applied as users configure the GFA Tool for use. Users can turn on and turn off certain
functions (e.g., AIRMET and SIGMET overlays for a given geographical area ). This can lead to hidden
areas of hazardous weather for a given flightpath.
Currently, the GFA Tool covers the CONUS, the Gulf of America, the Caribbean, portions of the Atlantic
Ocean, and portions of the Pacific Ocean , including the Hawaiian Islands and Alaska. The experimental
GFA Tool became available for Alaska in December 2020 and transitioned into operational status in
February 2022.
28.2.1 GFA Static Images
Some users with limited internet connectivity may access static images via the AWC ’s website as well as
from Flight Service’s website (see Appendix G, Websites). There are two static graphical images available
titled, “Aviation Clouds Forecast” and “Aviation Surface Forecast.” See Section 27.5 for more information.
28.3 FAA Flight Service’s Interactive Map
Similar in presentation and functionality to the GFA Tool for weather data and products is the interactive
map on Flight Service’s website. It provides users with interactive graphical capabilities to view a variety
of weather and aeronautical information. Users logged in to the website are able to enter basic route
information to display the flightpath on the map. Two primary types of weather information can be
displayed on the map: overlay data and weather imagery.
Overlay data includes the following and can be displayed simultaneously:
• Winds aloft,
• METARs,
• TAFs,
• PIREPs,
• SIGMETs,
Chapter 28, Aviation Weather Tools 28-3
• AIRMETs,
• CWAs, and
• NWS’ severe weather watches and warnings.
Weather imagery includes the following and can only be displayed one product at a time:
• Radar (NEXRAD precipitation),
• Satellite,
• CIP/FIP, and
• GTG.
Certain products will enable additional controls, such as an FL slider, a time slider, and animation controls.
Information on the above products and imagery is presented in other chapters of this handbook, as well as
in the User Guide provided on Flight Service’s website.
Appendix A, Cloud Types A-1
Appendix A Cloud Types
In each level, the clouds may be divided by type (genera). The definitions of the cloud types (given below)
do not cover all possible aspects, but they are limited to a description of the main types and of the essential
characteristics necessary to distinguish a given type from another type having a somewhat similar
appearance.
Clouds are identified based upon one ’s observation point at a particular elevation . From sea level, one
might observe stratus clouds enveloping the top of a mountain. However, on the mountaintop, one would
observe and report that same cloud as fog.
The exception to this is cumulus or cumulonimbus clouds over a mountain. Even though these low -level
clouds typically have bases under 6,500 ft (2,000 m), if one were to observe them over a mountaintop, their
base might be 12,000 ft (3,600 m) or higher relative to a particular location closer to sea level. However,
due to their location over the mountain, one would still call them cumulus or cumulonimbus clouds, as
appropriate.
A.1 High Clouds
Cirrus (Ci), cirrocumulus (Cc), and cirrostratus (Cs) are high-level clouds. They are typically thin and white
in appearance but can appear in a magnificent array of colors when the Sun is low on the horizon. They are
composed almost entirely of ice crystals.
A.1.1 Cirrus (Ci)
Cirrus (Ci) (see Figure A-1) is a cloud type composed of detached cirriform elements in the form of white,
delicate filaments of white, or mostly white, patches or narrow bands. These clouds have a fibrous (hairlike)
appearance and/or a silky sheen. Many of the ice crystal particles of cirrus are sufficiently large to acquire
an appreciable speed of fall; therefore, the cloud elements often trail downward in well-defined wisps called
“mares’ tails.” Cirrus clouds in themselves have little effect on aircraft and contain no significant icing or
turbulence.
Figure A-1. Cirrus (Ci)
Appendix A, Cloud Types A-2
A.1.2 Cirrocumulus (Cc)
Cirrocumulus (Cc) is a cirriform cloud type appearing as a thin white patch, sheet, or layer of cloud without
shading and is composed of very small elements in the form of grains, ripples, etc. The elements may be
merged or separate, and more or less regularly arranged; they subtend an angle of less than one degree when
observed at an angle of more than 30 degrees above the horizon.
Cirrocumulus (see Figure A-2) may be composed of highly supercooled water droplets as well as small ice
crystals, or they may be a mixture of both. Usually, the droplets are rapidly replaced by ice crystals. Pilots
can expect some turbulence and icing.
Cirrocumulus is not very common. It is composed of very small elements, which never show shading. The
cloud is frequently associated with cirrus or cirrostratus.
Figure A-2. Cirrocumulus (Cc)
A.1.3 Cirrostratus (Cs)
Cirrostratus (Cs) (see Figure A-3) is a cloud type appearing as a whitish veil and is usually fibrous (hairlike)
but sometimes smooth . Cirrostratus may totally cover the sky, and that often produces halo phenomena,
either partial or complete. Cirrostratus occasionally may be so thin and transparent as to render it nearly
indiscernible, especially through haze or at night. At such times, the existence of a halo around the Sun or
Moon may be the only revealing feature.
The angle of incidence of illumination upon a cirrostratus layer is an important consideration in evaluating
the identifying characteristics. When the Sun is high (generally above 50° elevation), cirrostratus never
prevents the casting of shadows by terrestrial objects, and a halo might be completely circular. At
progressively lower angles of the Sun, halos become fragmentary, and light intensity noticeably decreases.
When near the horizon, cirrostratus may be impossible to distinguish from cirrus.
Cirrostratus clouds are composed primarily of ice crystals and contain little, if any, icing and no turbulence.
Appendix A, Cloud Types A-3
Figure A-3. Cirrostratus (Cs)
A.2 Middle Clouds
Altocumulus (Ac), altostratus (As), and nimbostratus (Ns) are mid -level clouds. They are composed
primarily of water droplets; however, they can also be composed of supercooled liquid water droplets and/or
ice crystals when temperatures are below freezing. Altostratus is usually found in the middle level, but it
often extends higher. Nimbostratus is almost invariably found in the middle level, but it usual ly extends
into the other levels.
A.2.1 Altocumulus (Ac)
Altocumulus (Ac) (see Figure A-4) is a cloud type, white and/or gray in color, that occurs as a layer or
patch with a waved aspect, the elements of which appear as laminae, rounded masses, rolls, etc. These
elements usually are sharply outlined, but they may become partly fibrous or diffuse; they may or may not
be merged.
Small liquid water droplets invariably compose a major part of the composition of altocumulus. This results
in a sharp outline and small internal visibility. At very low temperatures, however, ice crystals may form.
Pilots flying through altocumulus can expect some turbulence and small amounts of icing.
The altocumulus in Figure A-4 is a single level, the greater part of which is sufficiently transparent to reveal
the position of the Sun and Moon. The clouds do not progressively invade the sky, and the individual
elements change very little. These thin altocumulus clouds usually produce a corona.