Well, the design is fully depend on your needs.
if this is a simple project (few forms) then you can go with ASP.NET web forms.
if this is a complex forms then it is better go with ASP.NET MVC
I think, displaying forecasting related things in one web form is the best way to give the information to viewers. Then they can easily get the idea what is going to happen. Personally, I would like to do that way.
If the report is a separate functionality, just like you want to get the current forecasting summary, then it is better use the popup for that functionally. you can give the link to view the report popup and by clicking that it will open the report