Hello -
You may want to look into using "adjustment variables" - from SAS Forecast Studio 14.2 User's Guide (chapter 6):
"What Is an Adjustment Variable?
Systematic variations and deterministic components are included in time series data. By adjusting the time series for known systematic variations or deterministic components, the underlying stochastic (unknown) time series process can be more readily identified and modeled. For more information about adjustment variables, see the "Adjustment Step" topic in the SAS Forecast Server Procedures: User’s Guide."
Thanks,
Udo