Need for a pivot table in the subtotal row the sum of column with averages.

MarcBergmans 

That is if you are not on Mac.

Creating PivotTable add data to data model

and when create two measures (in Power Pivot or right click on table name in PivotTable pane)

MD Average:=AVERAGE(_C70_ALMM_Extended[MD])

and

Sum by day MD Average:=SUMX( GROUPBY(_C70_ALMM_Extended, [RF]), [MD Average])

and use second one in PivotTable

Average of MD here is built-in measure and here is only to compare, you don't need it.

Please check in attached file.