I'm kind of surprised no one has answered...so I'll give it a shot even though my info is a few days out of date.
So starting from the Hot Metal Bridge, here is my report. Heading towards the sandcastle side: I have no idea.
Towards the southside, the entrance near 26th/25th street is pretty snowy. I tried to head down it a couple of weeks ago, got about 50ft and had to turn around. I'm not sure where that blockage ends... however on Wednesday I can report that the trail from near the Terminal building to 9th street seemed to be very clear. (I had to turn there so I didn't follow it any further, but as far as I could see it looked Ok-ish.)
Hope this helps and that you get a report on between 9th and 25th streets.