OK here's an update as of Friday morning.
If anyone is making their trip today, Philly should see a high of 60 degrees (yes, 60!) but rainy and windy. As rain diminishes, the temperature will drop significantly. Friday night's low will be 32 degrees, which is of concern if the precipitation lingers.
Saturday they are now forecasting a high of 50 degrees, partly cloudy with only a 10% chance of rain. Overnight low down to 31 degrees.
On Sunday, high will be 46 degrees, and partly cloudy with again only a 10% chance of precipitation. Dropping to an overnight low of 31 degrees, so it will start getting colder as you're on your way home.
So it sounds like temperatures will be comfortable for this Fest, and other than your potential Friday travels we should stay dry.
Source: The Weather Channel