I would not start monitoring it until the week of the event. The roads drain well, so even if it rained for 2 weeks straight, the roads would be bone dry and hard after 2 days of sun and wind. And, it can be very dry, and one good, soaking afternoon downpour late in the day can turn the roads to gooey mud.
I do not know what the name of the stream being crossed is otherwise I would give you the closest gauge station, but if someone could post that bit of information the link below can be used to find it.You may not be able to pull up the exact stream but you should find something in the area that will give you a feel for above or below average flow.
The weather has been pretty consistent throughout north central Pennsylvania. Showers...showers....showers...! The guys are exactly correct though...it is a pretty little stream and it can rise or fall considerably throughout the course of an afternoon!
The watershed area for Stony Fork is pretty small; you could gage the larger streams in the area, but probably not get a real picture of Stony Fork. The organizers will post the level of the stream on Friday at registration, and give an update on Sat if it has risen to difficult levels. If it gets too high, they will cancel the stage.
Rather than spend time on the water levels, I would do decent prep for the crossing as outlined in several posts, and then go worry about other things! The organizers will keep you up to date. I would worry more about a vary rainy Saturday turning the stages to goo, and seeing if I could procure a good set of mud tires, much more than the level of the water crossing. Muddy roads will be much more of a challenge to completing the event than the water crossing.