I'm a little confused and maybe it is just semantics - your post says that you want the 12 month moving average but you want to apply it to weeks -
with Tableau "weeks" you have the end of the month issue -
this formula returns the monthly impressions
On the week that is in part of each month there is s discontinuity - aso the average across the end of the month looks like this
Ok that said I used a rolling 52 on the monthly lod average to get the following
and it returns this
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