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

[Shutterstock]

Key Takeaways:

MOS (Model Output Statistics) is an automated weather forecast tool available in EFBs, providing aviation-relevant predictions for over 2,100 U.S. airports, significantly more than human-issued TAFs.
It works by statistically combining raw weather model forecasts with geoclimatic data and historical observations to account for local effects and downscale to aviation-specific elements like ceiling, visibility, and wind.
Crucially, MOS is an automated forecast and *cannot legally replace a human-issued TAF* for critical flight planning decisions (e.g., determining alternate requirements), serving best as supplementary guidance for airports without TAFs or to fill in details.
MOS has specific limitations, including inability to forecast multiple cloud layers, distinguish between definite and indefinite ceilings, predict certain vicinity phenomena (VCSH/VCFG), or variable winds.

See a mistake? Contact us.

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.