On Friday, there will be a low pressure trough that will be moving across the Great Lakes region, which will pick up moisture from the south and spread it across Pennsylvania through the day. The majority of this moisture will be in central and eastern PA, with the Pittsburgh area in the western edge of it. This keeps some uncertainty in the forecast regarding how much rain (if any) will be at the track on Friday, but for now I have a 40% chance in the forecast. With only a slight shift one way or the other, that rain chance could rise or lower in the next few days, so stay tuned.
The models are in pretty good agreement that the rest of the weekend will stay dry. Behind the departing trough, a large high pressure ridge off the east coast will build across the Southeast and Mid Atlantic region. This should steer any disturbances in the flow well north of the Pittsburgh area, and provide mostly sunny skies and warm temperatures in the mid 80s.