Low pressure is now forming off the coast of South Carolina and it will intensify rapidly over the next 12-24 hours as it moves slowly northeastward. The central pressure of the developing low pressure system is now at about 29.83 inches and it should deepen to about 29.18 inches by early tomorrow morning and then to near 28.94 inches by early tomorrow evening. There is some precipitation already showing up in the DC and Philly metro regions that is taking on all forms (i.e., rain, sleet and snow), but it is rather spotty and will become heavier and steadier near and after midnight.
9PM Observations: Dulles, VA 32 degrees, light snow; DCA light snow and 35 degrees, Pottstown, PA 32 degrees with light snow; Newark, NJ 33 degrees and cloudy
DC metro region: The DC metro region is likely to see quite a variation in snowfall amounts with up to 6 inches possible in and just southeast of the District and a foot possible in the far northern and western suburbs (e.g., northwest Montgomery (MD), northwest Howard (MD), and Loudoun (VA)). The snow will be mixed with sleet at times and the heaviest precipitation will occur from late tonight into early Tuesday. Winds will gust to 30 mph during the latter part of the storm.
Philly metro region: Heavy precipitation is going to fall tomorrow morning in the Philly suburbs and it could be a pretty amazing scene with heavy snow and strong winds. Late tonight and tomorrow morning the snow can fall heavily in SE PA with as much as 2 or 3 inches per hour during the height of the storm. Snow totals could range from 12-20 inches in the Philly metro region by the end of the storm. The city of Philly will see the lower amounts in that range as sleet will mix in for a longer period than it will in the northern and western suburbs where mainly snow will fall. The heavy snow and strong winds will make power outages a strong possibility due to the weight on tree limbs and wires. Winds will gust up to 40 mph during the latter stages of the storm.
NYC metro region: Blizzard conditions are likely for the NYC metro region as well with heavy snow and strong winds. Sleet will mix in at times in the NYC metro region where snow totals of 12-20 inches are likely with locally higher amounts even possible. The heaviest snow for NYC is likely to occur later tomorrow morning into the afternoon with 3 inches per hour possible. Winds can gust past 50 mph during the height of the storm and this will make power outages a strong possibility.
Coastal New Jersey: All NJ coastal locations can see wind gusts to 60 mph on Tuesday and snow will be substantial across northern sections where up to a foot can pile up, up to 6 inches or so in central sections, and up to 3 inches in southern NJ coastal regions where mixed precipitation will dominate.
One final note, as with many of the great snowstorms in the Mid-Atlantic region, some areas may experience thundersnow as the atmospheric dynamics will be quite strong during the rapid intensification phase of this major coastal storm system.
Meteorologist Paul Dorian