In 1999, there were no operational ensemble prediction systems within the NCEP model production suite, although there were some experimental, real-time advancements being made at the Environmental Modeling Center in collaboration with several universities and the THORPEX community on short and medium range ensemble prediction systems. Today, NCEP provides:

1) an operational Short Range Ensemble Forecast (SREF) updated four times per day run out to 84 hours, 2) an operational Global Ensemble Forecast System (GEFS) updated 4 times per day run out to day 16, which is included with the Canadian global model as part of the North American Ensemble Forecast System (NAEFS), and with the Naval Fleet Numerical global model as part of the National Unified Operational Prediction Capability (NUOPC), and 3) a Climate Forecast System (CFS) which will be included with EUROSIP (ECMWF, UKMet, Meteo France) to produce ensemble-based products focused on seasonal forecasts. With the rapid ongoing transformation from a single deterministic “model of the day” approach to a more ensemble-based model suite, one could argue that we have entered the second phase of the model revolution which has been the cornerstone for advancing the weather, climate and ocean predictive skill over the past 60 years, a goal of Krishnamurti's ongoing and groundbreaking work over the past 15 years.

The remarkable progress in the operational implementation of ensemble-based modeling systems spanning all scales from mesoscale to climate applications will be reviewed. The application of these ensemble systems to extreme weather and seasonal climate events and future work on storm-scale applications will be highlighted. The implications for future research and related R2O transition efforts will also be discussed, including the relationships between ensemble models and the connections to providing the levels of uncertainty in forecast products and recent advances in regional and global data assimilation techniques.