Many users here don't want to download Excel files because of virus potential, others have such things blocked by security software. Also if you give us Excel we have to create a SAS data set and due to the non-existent constraints on Excel data cells the result we end up with may not have variables of the same type (numeric or character) and even values.
Additionally formulas in Excel do not often translate to single or even simple statements.
I am not opening the Excel and really do not enjoy having to decipher supplied formulas at work when I have to, especially without any description of what the formula is supposed to actually do.
Is you data likely to have a seasonal component? If so data from end of winter to start of summer may not be a good fit for modeling end of summer to start of winter in general.
You may get better help for forecasting in the Forecasting section of the forum and including a description as well as to the type of formula/ forecasting approach is implemented.