Rook Yard at Greentree, PA is where they are based in the Pittsburgh area. The east end is not the busiest, or most predictable, portion of the WLE system. We had this topic come up some time ago, so I will link back to that thread.
I would expect WLE may not do all that much on a weekend, but you never know. However, if that is a bust, AVR should run their interchange train from Glenwood Yard to the NS at Island Ave. Yard.
http://forums.railpictures.net/showthread.php?t=11521
BTW, check the response from PLE Zero for a link to the WLE discussion board. Lots of recent discussion on activity, or lack thereof, on the east end.
Hope this helps out, and feel free to let us know how your trip goes.