 Edward Epstein recognized in 1969 that the atmosphere could not be completely described with a single forecast run due to inherent uncertainty , and proposed a stochastic dynamic model that produced means and variances for the state of the atmosphere . While these Monte Carlo simulations showed skill , in 1974 Cecil Leith revealed that they produced adequate forecasts only when the ensemble probability distribution was a representative sample of the probability distribution in the atmosphere . It was not until 1992 that ensemble forecasts began being prepared by the European Centre for Medium @-@ Range Weather Forecasts , the Canadian Meteorological Centre , and the National Centers for Environmental Prediction . The ECMWF model , the Ensemble Prediction System , uses singular vectors to simulate the initial probability density , while the NCEP ensemble , the Global Ensemble Forecasting System , uses a technique known as vector breeding . 
