Hi Akilees -
My suggestion would be to start with a univariate model and try to add complexity like input variables later.
Please have a look at PROC ESM as a start - you will need to make sure that you data is in time series format in order to use that (or any other time series forecasting) procedure.
Check out: http://support.sas.com/documentation/cdl/en/etsug/66100/HTML/default/viewer.htm#etsug_esm_gettingsta... as a starting point - you will find lots of information about time series data here: http://support.sas.com/documentation/cdl/en/etsug/66100/HTML/default/viewer.htm#etsug_tsdata_toc.htm
The way I see it you will need to do something like:
PROC ESM ...;
id week_ending interval=week;
forecast sizeAvol SizeBvol;
run;
Note that this code will run a simple ESM by default, so you may want to look at the model option of the FORECAST statement for more advanced models.
For more complex models, such as ARIMAX or UCM, which allow you to take independent variables into account please refer to either PROC ARIMA or PROC UCM.
All of these procedures are features in SAS/ETS software.
Thanks,
Udo