This was disclosed at the Aug. 9 TSB press conference.
TSB also announced that they would be trying to determine a more precise number, but that 50-100' is the best they were able to determine for TCH at the time.
[Speculation follows]
I can imagine that the approach end was largely VFR with a line of nasty CBs running north-south at what seemed far enough west of the airport at the FAF -- and too
close at the threshold.
Back at the FAF the view may have looked within acceptable parameters for a landing and the missed approach path may not have been assessed against the location of the CBs.
I suspect your average CB at that location would likely have allowed a normal landing. This one did not. So how do you tell the difference in time to decide properly?