What to expect
NWSRFS is a lumped, physically based, continuous hydrologic model currently containing a single snowmelt model and several rainfall-runoff models.

Note:
Lumped models do not explicitly take into account spatial variability of input, output, or parameters.
Physically based models simplify the physical system and can include empirical components.
Continuous models operate over an extended period of time (months).

RFCs use both empirical and conceptual rainfall-runoff models.

Note, by way of general definition:
All existing theoretical models simplify the physical system and often include obviously empirical components.
Nonetheless, they are regarded as conceptual models.
An empirical model is in reality a representation of data.

The empirical models utilize an Antecedent Precipitation Index (API)
as an indicator of moisture conditions.
   NWSRFS contains several event API models that compute only storm runoff.
   Recently a continuous model that utilizes the API concept was added to
   the system so that those who prefer the API approach can implement a model that
   can be used for ESP applications. It is referred to as the Continuous API Model.

The primary conceptual model used is the Sacramento soil-moisture
accounting procedure.

Both continuous models, Sacramento and Continuous API, can produce accurate simulations of all flow levels in wet areas, as long as the precipitation input can be reasonably defined.
The Sacramento model has a longer memory (weeks as opposed to days) and thus produces better results in drier areas.