The first Model Output Statistics (MOS) products were distributed by the National Weather Service (NWS) in the early 1970's. Since that beginning, the suite of products has grown in terms of weather elements, maximum forecast projection, frequency of production, and frequency of provided projections. In order to make this possible, rather complicated software systems were necessary for both development of the system and for its implementation on a routine basis.

The MOS system of software has undergone several iterations, some necessitated solely by the implementation of a new main-frame computer at the National Meteorological Center (NMC), now the National Centers for Environmental Prediction (NCEP). In the early days, considerable effort was put into making the code efficient, and partly for that reason the change from a 60-bit machine to a 32-bit machine caused havoc with the system. Until recently, the MOS software systems were build for main-frames.

In the early 1990's, it became clear our systems had to be rebuilt to take advantage of new technology. Consequently, an effort was started in 1993 that has led to a completely new software system of considerably more capability than the one it replaces. This new system and how it is influencing the guidance products created by the Meteorological Development Laboratory (MDL), formerly the Techniques Development Laboratory (TDL), will be described.