ECMWF Ensemble Model Description

European Center for Medium Range Weather Forecasting Integrated Forecast System

The ECWMF ensemble model is run twice a day at 0z and 12z out to 10 days in the future. The ECWMF model runs both in a "deterministic forecast" mode and as an ensemble. Deterministic refers to cause and effect. An ensemble forecast takes the output from many deterministic models and creates an average or consensus. The graphic above shows the ECWMF ensemble model.

Consensus forecasts are obtained by combining the forecasts from a collection (or "ensemble") of models, where the ensemble can either consist of multiples runs of a single model or runs from different independent models. The simplest way to form a consensus is to average the output from each member of the ensemble, e.g., one computes the mean of each member's predicted latitudes and longitudes of the tropical cyclone center at some forecast time. On average, consensus forecasts are more accurate than the predictions from their individual model components.

The graphics above show the barometric pressure field. Lower pressures are indicated in dark blue. Higher pressures are indicated in red. Hurricanes and tropical storms, as well as non-tropical low-pressure areas are associated with low pressure (Blue). The white lines are isobars (lines of equal pressure). The closer the lines are to each other, the stronger the winds.

Remember that these are mathematical models with varying initial assumptions. Thus, different models produce different final results. They do not necessarily reflect the "official" hurricane track issued by the National Hurricane Center. Forecasters review all of the model data but use their own experience and scientific expertise to arrive at a final forecast.