The predictors are typically forecasts from a numerical weather prediction (NWP) model, climatic data, and, if applicable, recent surface observations.
In contrast, despite the enormous amount of computing resources devoted to generating them, ensemble model forecasts' relative frequency of events—often used as a proxy for probability—do not exhibit useful reliability.
[3] Thus, ensemble NWP model output also requires additional post-processing in order to obtain reliable probabilistic forecasts, using nonhomogeneous Gaussian regression[4] or other methods.
[5][6] MOS was conceived and planning for its use began within the U.S. National Weather Service’s (NWS’s) Techniques Development Laboratory (TDL) in 1965 and forecasts first issued from it in 1968.
[9] There are eight sets of MOS guidance available from MDL, operational and experimental, covering the span of time from the next hour out to ten days for the United States and most of its territories.
This requirement is necessary in order to fully capture the model's error characteristics under a wide variety of meteorological flow regimes for any particular location or region.
Extreme meteorological events such as unusual cold- or heat-waves, heavy rain and snowfall, high winds, etc., are important in the development of robust MOS equations.