The stalled front that is bringing today's damp and raw weather will lift north through the region over the course of tonight and cross through Philadelphia on Monday morning. It will be a mild, perhaps even warm Monday as the warm front pushes up along the East Coast through the course of the day with southwest breezes aloft and at the surface helping push warmth along.
How warm could Monday get? Well, the higher resolution modeling like the NAM are suggesting middle 60's for highs from Philadelphia and Southeast Pennsylvania on south. Monday's record high is 71 so it'll be pretty tough to reach that in the city...but we'll still get within a few degrees of it. While it will be mild, sunshine will be a bit of a premium locally...might be some sun down in Southern Delaware or down towards Washington but we will probably be stuck locally under gray skies.
Rainfall with the front will vary -- some spots could pick up locally heavy rains and could see over a half an inch on Monday, especially if the modeled line of heavier rain projected on the NAM model up above does indeed develop -- other spots will get a modest amount of rain on the order of a quarter inch or less.
In the wake of the frontal boundary passage will be a gradually cooler temperature pattern for Tuesday through the balance of the week but temperatures will step down to normal or just above that for the balance of the week after Monday's front moves through.