Use External Variable if the lookup table or relationship you need to define varies as a function of a variable whose values are stored in a time series that you will provide to as input to the model.
A Variable Name text field—The name you enter will appear in the Alternative Editor's Time Series tab; this is where you will identify the HEC-DSS time-series dataset that represents the External Variable. Enter an appropriately descriptive name in the Variable Name field so that you will know what time-series to use for each External Variable you create in your model.
A set of Time Series Options—these options apply to the input time series representing the external variable and are described in detail in "Function of: Model Variable".
