Are There Any Amendment Criteria for a TAF?

When there’s a discrepancy, an aviation weather forecaster can make an update.

Scott Dennstaedt, Ph.D

Wednesday, January 04, 2023 at 01:34 PM ET

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When there’s a discrepancy, an aviation weather forecaster can make an update. [Credit: iStock]

Key Takeaways:

TAF amendments are triggered by local NWS forecasters when the forecast elements (ceiling, visibility, wind, weather) significantly deviate from observed or expected conditions, especially if the change is anticipated to persist for 30 minutes or longer or alters the flight category.
Specific amendment criteria include changes in flight category (VFR, MVFR, IFR, LIFR), wind speed/gusts (e.g., ≥10 knots difference), the unexpected occurrence or non-occurrence of severe weather (thunderstorms, freezing precipitation, ice pellets), or low-level wind shear.
Forecasters use Aviation Forecast Prep Software (AvnFPS) to monitor current observations against TAFs, which flags discrepancies that meet amendment thresholds. For busy airports, routine 2-3 hourly updates are also treated and tagged as amendments.

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Question: Can you tell me if there are any amendment criteria for a TAF (terminal aerodrome forecast)? If so, what are they and how are they applied?

A. Most of the official aviation weather forecasts you will get on a standard briefing or via your favorite heavyweight aviation app or website are issued by aviation meteorologists located at the Aviation Weather Center (AWC) in Kansas City, Missouri. This includes graphical AIRMETs (G-AIRMETs), SIGMETs (WS) and convective SIGMETs (WST). Terminal aerodrome forecasts or TAFs, however, are not issued by the AWC nor are they issued by Flight Service; they are issued by forecasters physically located at your local NWS Weather Forecast Offices (WFO) throughout the United States and its territories shown below. The meteorologists at the local WFOs are very familiar with any local weather effects and have the best opportunity to produce a quality forecast for aviation.