PivotTable's Report Filter using "greater than"
I know this is a bit late, but if this helps anybody, I think you could add a column to your data that calculates if the probability is ">='PivotSheet'$D$2"
(reference a cell on the pivot table
sheet).
Then, add that column to your pivot table and use the new column as a true/false
filter.
You can then change the value stored in the referenced cell to update your probability threshold.
If I understood your question right, this may get you what you wanted. The filter value would be displayed on the sheet with the pivot and can be changed to suit any quick changes to your probability threshold. The T/F Filter can be labeled "Above/At Probability Threshold" or something like that.
I've used this to do something similar. It was handy to have the cell reference on the Pivot table sheet so I could update the value and refresh the pivot to quickly modify the results. The people I did that for couldn't make up their minds on what that threshold should be.
In an Excel pivot table, you are correct that a filter only allows values that are explicitly selected. If the filter field is placed on the pivot table rows or columns, however, you get a much wider set of Label Filter conditions, including Greater Than. If you did that in your case, then the added benefit would be that the various probability levels that match your condition are shown in the body of the table.