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 issued by local NWS Weather Forecast Office forecasters when the current forecast fails to accurately represent actual or expected conditions, particularly if discrepancies are projected to persist for 30 minutes or longer, or if new information indicates a change in the future flight category.
Key amendment criteria involve changes in categorical thresholds for ceiling and visibility (VFR, MVFR, IFR, LIFR), significant deviations in wind speed or gusts (e.g., ≥ 10 knots difference), and the unforecasted occurrence or absence of specific weather phenomena such as thunderstorms, freezing precipitation, ice pellets, or non-convective low-level wind shear.
Forecasters use Aviation Forecast Prep Software (AvnFPS) to continuously monitor observations against the TAFs, which flags potential discrepancies that may require an amendment, though brief, non-category-altering weather events typically do not warrant one.
In high-traffic areas like Chicago, Atlanta, and New York, TAFs are issued more frequently (every 2-3 hours); these regular updates are tagged with "AMD" (amended) even when they are routine new forecasts, not necessarily indicating a change due to criteria being met.

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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.