The EFAS long-range forecasts comprise two model systems; seasonal (SEAS) and sub-seasonal to seasonal (S2S) outlooks. The two systems use different meteorological forcing in their model chain and are issued with different frequency. The SEAS forecast is issued at monthly where as the S2S is issued twice weekly, on Mondays and Thursdays.
The forecasts provide hydrological outlooks which show the likelihood of high or low flows within the coming eight weeks in a region (aggregation of river basins). They are created by comparing the forecast with EFAS low and high flow thresholds, each averaged over the defined regions. The schematic below illustrates how the EFAS seasonal and sub-seasonal outlooks are produced.
Schematic view of steps in producing EFAS seasonal and sub-seasonal forecasts