Dynamical extended range forecasting
From AMS Glossary
dynamical extended range forecasting
(Abbreviated DERF.) Forecasting the state of the atmosphere (using a numerical weather prediction model with observed initial conditions) beyond the range for which individual cyclonic-scale disturbances are predictable.
Although, in general, the useful information regarding cyclonic-scale disturbances has been lost in the extended range, the behavior of large-scale, lower-frequency phenomena may still be predictable.