4.5 Weather Collection, NWS Facilities, GFA, and EWINS

Obtain Weather from Appropriate Sources

A dispatcher must understand how weather is observed, forecast, disseminated, and used. The syllabus includes National Weather Service functions, data-collection systems, analysis/forecast facilities, and service outlets. The practical test assesses whether the applicant can assemble an appropriate briefing, not merely identify abbreviations. Source authority, data age, geographic scope, and limitations determine whether a product supports the proposed decision.

Collection systems

ASOS and AWOS measure airport weather using automated sensors, with capabilities varying by system. A human observer can augment observations where authorized, identify phenomena a particular automated system does not resolve, and supply additional remarks. A station marked AUTO should not be assumed to have the same observation capability as every other station. Sensor outages and missing groups matter operationally.

Radiosondes provide vertical temperature, humidity, pressure, and wind measurements. Radar observes precipitation-related returns and movement, with beam-height, attenuation, clutter, and sampling limitations. Satellites provide imagery and atmospheric information over wide areas, including oceanic regions without ground radar. Aircraft observations and PIREPs add in-situ information, but their time, position, altitude, and aircraft type must be considered.

A numerical weather model combines observations with a forecast system. A model field is neither a direct measurement at every point nor a guarantee of future conditions. Forecast uncertainty grows with the situation and time horizon. An absence of pilot icing reports can reflect lack of aircraft sampling rather than proof of no icing.

NWS and related facilities

These services complement each other. A convective outlook is valuable for broad risk assessment but does not replace a destination TAF or required approved weather information. A CWA can provide a rapid local update while a national advisory supplies the broader context. Know the issuing facility and the actual product's responsibility area before interpreting it.

GFA and area forecasts

Graphical Forecasts for Aviation (GFA) provide layers for weather, cloud, visibility, winds, and hazards over selectable periods. Use the legend, level, and valid time. A flight-category layer can reveal a region of low ceilings, while an icing layer helps assess the descent or diversion altitude. No single layer contains every requirement for a Part 121 release.

Traditional CONUS text area forecasts were replaced by graphical information. Hawaii's text FA was retired in January 2025; Alaska retains its regional FA system. Text AIRMET retirement over CONUS is a separate change from area-forecast replacement. Do not announce that every “FA” or “AIRMET” everywhere in the world has been retired. The syllabus's older product names must be studied with their present geographic applicability.

EWINS and carrier forecasts

An Enhanced Weather Information System (EWINS) is an authorized carrier weather system used under the applicable FAA approval and procedures. It can provide approved forecasts supporting specified operations. It does not mean any dispatcher may improvise a terminal forecast, disregard unfavorable government products, or use an unapproved internet prediction to satisfy a release rule.

Section 121.101 identifies weather-reporting facility requirements for domestic and flag operations, including approved sources. Obtain the carrier's current authority and weather procedures before relying on a forecast product for a legal destination or alternate decision. The operational value of a product and its authority for a particular required weather determination are separate questions.

Briefing types and service outlets

For preparation, assemble route, destination, alternate, and airport-condition information through the carrier's authorized weather system and appropriate official sources. Flight Service briefing terminology includes standard, abbreviated, and outlook briefings. An abbreviated update assumes the earlier briefing and supplied changes are understood; it does not establish that omitted hazards were checked. A dispatcher needs the actual operational package relevant to the release.

Service outlets can deliver identical source information with different graphics or latency. A vendor's map symbol is an interpretation of the underlying bulletin. Read the original text when timing, vertical extent, movement, or a special condition matters. Record issue/validity times and whether a bulletin has been superseded. Repeating an old product through a new display does not make it current.

Worked source-conflict exercise

A fictional airport's automated observation has a missing visibility sensor. A vendor graphical layer depicts VFR, a nearby station reports fog, and the destination TAF forecasts a low ceiling at arrival. The dispatcher first determines which approved observations or alternatives are available for the airport and what the missing sensor means. The nearby report gives context but is not automatically the destination's required report. The graphical layer does not erase the TAF or authorize dispatch below applicable weather requirements.

Then assess the route and alternate windows with the appropriate forecasts, identify any applicable authorized forecast system, and explain the source chosen for each decision. Contact the authorized weather/operations personnel if a necessary input is unavailable or conflicting. Do not fill a missing legal value with a guessed observation merely to complete the computer release.

Maintain the weather picture in flight

After departure, obtain updated terminal forecasts, observations, PIREPs, advisories, and field reports affecting active flights. Under § 121.601, the dispatcher provides additional available safety-related meteorological and facility information to the PIC. A briefing is a continuing process, with a new evaluation after a significant route, altitude, ETA, aircraft-status, or alternate change. Explain how each product changes the plan rather than sending a large unprioritized package and assuming the crew has identified the urgent item.

Official References

Source check: 2026-10-12. 2026 FAA Aviation Weather Handbook; Current NWS TAF policy (October 2024); AWC current products; Dispatcher weather information § 121.601. For operational use, apply current issued authorizations and the assigned aircraft’s approved data.