A cold front will move through Sunday evening. Before that time, high temperatures may reach 94º-95º in the Philadelphia area today around 3-4 PM. Still low dew points near 60º or less, keeping it more comfortable than a typical summertime ninety degree day in Philadelphia.
Some models (HREF, Canadian HRDPS) have a low probability of a widely scattered shower or thundershower making it into Philadelphia between 6 and 9 PM. There’s just enough convective available potential energy (CAPE), marginal instability and available moisture. Most areas won’t see any rain.