First and foremost, this storm is another major rain event for the entire Mid-Atlantic region. Heavy rain continues throughout the region with over 1.5 inches already recorded for the day at Reagan National Airport in Washington, D.C. and enough rain in Philly to boost its year-to-date totals to over 60 inches for the first time in modern record-keeping. The all-time unofficial rainfall record from 1867 is 61.17 inches and even that is in jeopardy from today's storm. Heavy rain will continue right through the evening hours and thunderstorms could even mix into the picture. Later tonight, the combination of colder air moving into the upper atmosphere and colder air moving in at the surface from our northwest will change the rain to snow to around the I-95 corridor and points north and west. This rain/snow line will generally advance from the west to the east and the timetable for the changeover here in the Philly metro region is between 1 and 3AM. The snow should last for a few hours in the northern and western suburbs (e.g., Chester, Montgomery, Bucks Counties) with likely accumulations of 1-3 inches and an inch or less in Philly. Snow ends here at or before 7AM or so and the sun returns tomorrow, but it'll be brisk and cold.