ECMWF has extended the range of weather forecast products that are available freely and with no restrictions from its web site. The new products are from the ECMWF ensemble prediction system (EPS) that provides guidance on the day-to-day predictability of the atmosphere. This gives an important complement to the information that is already available from the single deterministic model.
The ensemble is a set of 51 separate forecasts made by the same computer model, all started from the same initial time. The starting conditions for each member of the ensemble are slightly different. The differences between these ensemble members tend to grow as the forecasts progress. This dispersion varies from day to day, depending on the initial atmospheric conditions, and therefore gives an indication of the uncertainty in the current forecast.
The new graphical products show the ensemble mean (average over all 51 members) and ensemble standard deviation (spread) corresponding to each parameter available from the deterministic model: 500 hPa geopotential, 850 hPa wind and temperature and mean sea level pressure.
