 Because the output of forecast models based on atmospheric dynamics requires corrections near ground level , model output statistics ( MOS ) were developed in the 1970s and 1980s for individual forecast points ( locations ) . The MOS apply statistical techniques to post @-@ process the output of dynamical models with the most recent surface observations and the forecast point 's climatology . This technique can correct for model resolution as well as model biases . Even with the increasing power of supercomputers , the forecast skill of numerical weather models only extends to about two weeks into the future , since the density and quality of observations — together with the chaotic nature of the partial differential equations used to calculate the forecast — introduce errors which double every five days . The use of model ensemble forecasts since the 1990s helps to define the forecast uncertainty and extend weather forecasting farther into the future than otherwise possible . 
