AIM

8/15/19

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Meteorology

information. The FAA has determined that operators
and pilots may utilize the following approved sources
of aviation weather information:

1. Federal Government.

 The FAA and NWS

collect raw weather data, analyze the observations,
and produce forecasts. The FAA and NWS
disseminate meteorological observations, analyses,
and forecasts through a variety of systems. In
addition, the Federal Government is the only
approval authority for sources of weather observa-
tions; for example, contract towers and airport
operators may be approved by the Feder

al

Government to provide weather observations.

2. Enhanced Weather Information System

(EWINS).

 An EWINS is an FAA authorized,

proprietary system for tracking, evaluating, report-
ing, and forecasting the presence or lack of adverse
weather phenomena. The FAA authorizes a certifi-
cate holder to use an EWINS to produce flight
movement forecasts, adverse weather phenomena
forecasts, and other meteorological advisories. For
more detailed information regarding EWINS, see the
Aviation Weather Services Advisory Circular 00

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and the Flight Standards Information Management
System 8900.1.

3. Commercial Weather Information

Providers.

 In general, commercial providers pro-

duce proprietary weather products based on
NWS/FAA products with formatting and layout
modifications but no material changes to the weather
information itself. This is also referred to as
“repackaging.” In addition, commercial providers
may produce analyses, forecasts, and other propri-
etary weather products that substantially alter the
information contained in government

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produced

products. However, those proprietary weather
products that substantially alter government

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pro-

duced weather products or information, may only be
approved for use by 14 CFR Part 121 and Part 135
certificate holders if the commercial provider is
EWINS qualified.

NOTE

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Commercial weather information providers contracted by
FAA to provide weather observations, analyses, and
forecasts (e.g., contract towers) are included in the Federal
Government category of approved sources by virtue of
maintaining required technical and quality assurance
standards under Federal Government oversight.

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4. Graphical Forecasts for Aviation

(GFA)

a.

The GFA website is intended to provide the

necessary aviation weather information to give users
a complete picture of the weather that may affect
flight in the continental United States (CONUS). The
website includes observational data, forecasts, and
warnings that can be viewed from 14 hours in the past
to 15 hours in the future, including thunderstorms,
clouds, flight category, precipitation, icing, turbu-
lence, and wind. Hourly model data and forecasts,
including information on clouds, flight category,
precipitation, icing, turbulence, wind, and graphical
output from the National Weather Service’s (NWS)
National Digital Forecast Data (NDFD) are available.
Wind, icing, and turbulence forecasts are available in
3,000 ft increments from the surface up to 30,000 ft
MSL, and in 6,000 ft increments from 30,000 ft MSL
to 48,000 ft MSL. Turbulence forecasts are also
broken into low (below 18,000 ft MSL) and high (at
or above 18,000 ft MSL) graphics. A maximum icing
graphic and maximum wind velocity graphic
(regardless of altitude) are also available. Built with
modern geospatial information tools, users can pan
and zoom to focus on areas of greatest interest. Target
users are commercial and general aviation pilots,
operators, briefers, and dispatchers.

b. Weather Products.

1.

The Aviation Forecasts include gridded

displays of various weather parameters as well as
NWS textual weather observations, forecasts, and
warnings. Icing, turbulence, and wind gridded
products are three

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dimensional. Other gridded

products are two

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dimensional and may represent a

“composite” of a three

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dimensional weather phe-

nomenon or a surface weather variable, such as
horizontal visibility. The following are examples of
aviation forecasts depicted on the GFA: 

(a)

Terminal Aerodrome Forecast (TAF)

(b)

Ceiling & Visibility (CIG/VIS)

(c)

Clouds

(d)

Precipitation / Weather (PCPN/WX)

(e)

Thunderstorm (TS)

(f)

Winds

(g)

Turbulence

(h)

Ice