Source Opportunity Weighted Total via Saved Search. It is a current limitation for Saved Transaction Search to pull up the Weighted Total field. And Enhancement 87740 is requested to address this limitation.
Navigate to Lists > Search > Saved Searches > New
Select Transaction
Search Title: Enter a Title
Click Results tab
Click Columns subtab:
Field:
Select Formula (Numeric)
Formula column: Enter ({CONTRIBUTION}*{PROJECTEDAMOUNT})*{PROBABILITY}
Custom Label column: Enter Opportunity Weighted Total
Click Save & Run