I believe the best approach is to create two spreadsheets (let's name them Sheet A and Sheet B). The first bar char should be placed on Sheet A, and the second bar char should be placed on Sheet B. (the forecasting).
After that, you may make a dashboard with both of them aligned horizontally.
You'll most likely need to align the axes of the two worksheets using (for example) this guide.
For reference, follow this link.