What Is a MOS Forecast?

For an airport without a TAF, a MOS forecast can provide some useful guidance about expected meteorological conditions—but it has some limitations.

Scott Dennstaedt, Ph.D

Wednesday, October 04, 2023 at 05:09 PM ET

Verified

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Key Takeaways:

MOS (Model Output Statistics) is an automated forecast system that combines raw model data with statistical methods and geoclimatic information to provide aviation-specific weather guidance for over 2,100 airports, significantly more than official TAFs cover.
While useful for supplementing information or at airports lacking a TAF, MOS should never be used as a legal replacement for a human-issued TAF when one is available, especially for critical flight planning decisions like alternate requirements.
MOS provides forecasts for elements like ceiling, visibility, and wind, and accounts for local topography, but it has limitations, such as inability to forecast multiple cloud layers, variable winds, or distinguish certain precipitation details.

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Question: The EFB I use has an option for MOS forecasts… What is that and can that be used legally for planning a flight?

Answer: MOS stands for model output statistics and is pronounced “moss.” MOS has been around since the 1960s and was originally developed to provide aviation meteorologists with guidance to produce useful forecasts to pilots. But over the last decade, MOS has been making its way into the aviator’s toolkit and is offered by a couple of the heavyweight electronic flight bag (EFB) apps.