MOS stands for Model Output Statistics. As the name suggests, MOS is derived from the output of weather prediction models developed and run by research meteorologists at NOAA. The use of MOS has actually been around for decades, but has only recently been introduced for aviation use.
MOS transforms the model data into weather elements that the model does not directly forecast. This includes sensible weather elements basic to aviation such as sky cover, ceiling height, visibility, wind speed and direction, the probability of precipitation, and the precipitation type.
MOS is such a great tool that it’s used by local NWS forecasters all over the US to create more accurate local forecasts for specific towns or cities. These forecasters also rely on MOS as one form of guidance to construct and amend a TAF. While TAFs provide the official forecast for 635 airports throughout the US and its territories, MOS provides weather guidance for over 1800 airports including some military air bases.
MOS is especially accurate in the first 6 hours and, since it is location specific, will usually provide you with more detailed guidance than using the area forecast (FA) alone. One thing to note, however, is that MOS should never be used for legal requirements such as determining an alternate on an IFR flight plan (more on that below).
Another distinct benefit to pilots is that MOS is updated hourly. You’ll get a refreshed forecast at an airport that will tend to track better with the actual weather than with the area forecast. Moreover, MOS is highly tailored for each airport. So if the airport is in a valley or near an ocean or next to a river, MOS is aware of the nearby terrain features and local effects of the weather for that airport.
