Within EFAS the LISFLOOD hydrological model is run as a continuous simulation using interpolated observed meteorological data. This simulation provides the initial conditions for the EFAS forecasts. The simulated snow accumulation is represents the amount snow stored on the land surface. It can be provided either as a snow water equivalent volume or as an anomaly.
The anomaly is computed for the average snow water equivalent over the past ten days. It is calculated using the long term average (m) and standard deviation (s) of the average snow water equivalent over the past ten days as
where X is the current average snow water equivalent. The long term average and standard deviation are taken from a 22 year simulation of LISFLOOD.