Weak low pressure is now forming over the Southern Plains and it will head northeast over the next 24 hours to a position just off the Mid-Atlantic coast by late tomorrow. Precipitation in the form of a rain/snow mix will likely reach the Philly metro region around daybreak. The northern and western suburbs of Philly should then see the mixed precipitation changeover to mainly snow during the morning hours and accumulations of 1-3 inches are possible by later in the afternoon with lesser amounts expected from the city of Philly to points south and east. The snow will wind down early tomorrow night and temperatures will drop into the 20’s in the overnight hours after reaching daytime highs in the upper 30’s.
One thing we’ll have to watch for on Tuesday is the possible quick intensification of the low pressure region as it reaches the western Atlantic Ocean just off the Mid-Atlantic coastline. There has been a subtle trend in recent computer forecast model runs (see video) to “hang” the system back somewhat late tomorrow as some intensification occurs. Additionally, there is currently an impressive-looking southern stream system near the Texas/Mexico border region that appears to be underplayed by the computer models and this feature could aid in late day intensification of the low pressure near the Mid-Atlantic coastline. The bottom line is that all of this could act to prolong the snow event across SE PA and interior New Jersey later tomorrow and early tomorrow night.