Calendar effect in forecasting

As we know last weekend was long holiday for US. Our sales was also affected.  So for forecasting can anybody suggest how to include calendar effects in ARIMA model using SPSS or any other way.  I created one event variable and put ‘1’ for event and zero for others and took this as the independent variable in the ARIMA Model.

My model is giving best fit for past months (April, May, June) but this month july it is not going good. I took two years data day wise and I have to forecast for july daywise.  Please help…..