Edited for clarity:
How deep will the river be at boundary creek if the river is below 2'? You can probably wade across at boundary creek below 2'. Just below boundary there are 20' plus deep pools. Just below that there are places probably 5" deep maximum. This question doesn't really make sense. Because the gauge is way downstream.
Plus, It isn't the depth. It is the number of daggers sticking up through said water waiting to gut your raft.
An alternate version of this was discussed earlier this week. here is my conclusion:
If the gauge is below 2', regardless of the conversion, the upper river is very bony and technical. It doesn't really matter if that means 973 or 942 CFS or whatever. One would need to pack light and be ready to work for it or be very skilled in the art of rock nudging. I understand we are all internet nerds who like to look at historical data and try to unravel the trends and plan things out precisely. But as a certified Idaho native and fellow nerd I can say this year is grim. By your date the top will be very bony.
Go of the top IF:
1) you have strong technical boating skills
2) you are willing to leave many luxuries behind
3) you have 1 passenger max per boat
4) You understand it will feel a bit like work at times
Fly in IF:
1) you love the beers and the ices
2) You have no desire to get out of your boat and yank on the handles in waist deep water
3) you don't have a lot of time
4) Maybe the skill set isn't super sharp
I'm going to sin now and discuss the MFS in CFS.
If the Middle fork lodge gauge is above 1200cfs most groups should be OK reasonably packed.
If the Middle fork lodge gauge is below 1000cfs most groups should throw out some passengers and gear and go.
If the Middle fork lodge gauge is below 750cfs most groups should fly in.
If the Middle fork lodge gauge is below 500cfs only the most masochist of small groups should go with gear specifically suited to the task.
500 at the lodge probably means >300 at the launch. that just isn't much water to work with.
You are from boise. The middle fork is probably roughly comparable to staircase on the SF Payette at given flows IMO. Take your boat to staircase this weekend, throw 4 people on it and run that 4 miles. Now decide if you want to do that for 25 miles in the wilderness. lo0oks like staicase is 900ish, very comparable to 2' IMO. Have fun.