# Model output statistics

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Model output statistics

Model Output Statistics (MOS) is an omnipresent statistical technique that forms the backbone of modern weather forecasting. The technique pioneered in the 1960s and early 1970s is used to post-process output from numerical weather forecast models. Generally speaking, numerical weather forecast models do an excellent job of forecasting upper air patterns but are too crude to account for local variations in surface weather. Pure statistical models, on the other hand, are excellent at forecasting idiosyncrasies in local weather but are usually worthless beyond about six hours. The MOS technique combines the two, using complex numerical forecasts based on the physics of the atmosphere to forecast the large-scale weather patterns and then using regression equations in statistical post-processing to clarify surface weather details. The accuracy is generally far better than either a pure statistical model or a pure numerical model (NWP).

## Definition

Because forecast models on their own do not reliably determine weather conditions near ground level, statistical models based upon the three dimensional fields output from numerical weather models, surface observations, as well as the climatology for specific locations were developed. These statistical models are called Model Output Statistics (MOS).

## History

MOS was developed by the National Weather Service for their suite of weather forecasting models by 1976. The United States Air Force developed their own set of MOS based upon their dynamical weather model, the NOGAPS, by 1983. This differs from the perfect prog technique, which assumes that the output of numerical weather prediction guidance is perfect.

MOS has a very small field of practitioners. The most often cited pioneers are Glahn, Lowry, and Klein. Currently, most work in the field is done from the Meteorological Development Lab (MDL) . Significant work has been contributed to the field by Murphy, Dallavalle, Mass, Vislocky, Fritsch, Allen, Hughes, and Antolik. 

## Current operational forecasts

MOS is run operationally using millions of equations from the MDL. As of 2010, the NAM, GFS (short and long range) and 22-member GFS ensemble are used to create MOS products; the NGM-derived MOS products were discontinued in March 2009. (List of MOS products from the MDL)

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