AIM 

4/20/23 

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Not all sources of aviation weather information are able to provide all three types of weather 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 
observations; 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, reporting, and forecasting the presence or lack of adverse weather phenomena. 

The FAA authorizes a certificate 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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45 and the Flight Standards Information Management 

System 8900.1. 

3.  Commercial Weather Information Providers.

 In general, commercial providers produce 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 proprietary 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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produced 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, turbulence, 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 phenomenon 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) 

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Meteorology