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:

Terminal Aerodrome Forecasts (TAFs) are issued by local NWS Weather Forecast Offices (WFOs) and are amended when observed or expected weather conditions significantly differ from the forecast and are anticipated to persist for at least 30 minutes.
Amendment criteria encompass changes in flight categories (VFR, MVFR, IFR, LIFR), significant deviations in wind speed, direction, or gusts (e.g., ≥ 10 knots difference), and the unexpected occurrence or non-occurrence of phenomena like thunderstorms, freezing precipitation, or low-level wind shear.
Forecasters utilize software (AvnFPS) to continuously monitor TAF sites against observations, alerting them when differences approach or exceed amendment thresholds. For high-traffic airports (e.g., Chicago, Atlanta), TAFs are updated more frequently (2-3 hourly) and are tagged as "AMD," which may signify a routine update rather than a specific amendment due to forecast deviation.

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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.