While it was cold yesterday and still chilled today, we will experience a pretty significant moderation in temperatures in parts of the region tomorrow as a storm system cuts through the Great Lakes, pulls in milder air aloft and at the surface for the southern half of the region, and brings rain to the Delaware Valley.
Rain approaches the region in the predawn hours, spreading in from the southwest and moving northeast through the day. Temperatures at the surface in the city should be above freezing at the beginning of the event (although not by much) so rain will not be prone to icing up roads in Philly or points south. North and west is a different story, especially above Allentown. This won't be a long duration icing event but as rain initially falls in the Lehigh Valley, the hills in Central and North Jersey, and the Poconos temperatures will be around or just below freezing, which will yield areas of freezing rain at the start. It will not be all freezing rain up there but there will probably be enough to yield a few slick spots on the way to work tomorrow morning.
By mid morning, most areas should be safely above freezing except a few pockets of the Poconos, where temperatures may be around 32 or just below it. Milder air aloft and at the surface will scour most of the subfreezing air out of the region, resulting in rain for the balance of the event in the city. Rainfall amounts could range between a half inch and a full inch as a strong low level jet pulls moisture northeastward. Rainfall will be steadiest, perhaps heaviest, between 7 and 11 AM before tapering to showers and drizzle on the back end of the event.
Temperatures will vary tremendously tomorrow afternoon across the region -- 30's are likely to our north over the Poconos as the push of warmth may have difficulty getting over the various ridges and hills and cooler air pools across those typically colder areas in these types of events. Wouldn't surprise me if some 30's were also lurking in parts of Central Jersey in some of the valleys that lock in cold a bit more effectively. However, the push of warmth at the surface will yield 50 or warmer for Philly (Airport, Center City) and points south tomorrow afternoon, with 60's into Maryland and perhaps Southwestern Delaware. We could have another 25 degree spread in temperatures between Mount Pocono and Dover around 4 or 5 PM tomorrow afternoon.
We could perhaps see some sun south and west of the city tomorrow afternoon towards sunset -- particularly down near Dover, Wilmington, and towards Baltimore if this system departs as we're thinking it will. Philly and northeast probably don't see any sunshine tomorrow.