Last Updated: 10:30am Saturday, February 17th, 2018 by MP
Near Term (through tonight)
Canadian high pressure will begin sliding offshore today. Sunshine this morning will give away increasing clouds this afternoon and winds will become light out east-southeast. High temperatures should reach the mid-upper 30s, perhaps around 40 near the shore.
A robust shortwave trough moving quickly over Midwest and Ohio Valley today, will be partial phasing with some southern stream sheared-out shortwave energy tonight. This will cause another wave of low pressure will be forming along the cold front stalling over the Lower Mid-Atlantic region today. The pattern continues to be progress with semi-zonal flow and a lack of high-latitude blocking. However enough height rises with the Southeast ridge, will actually help this shortwave trough amplify a bit before reaching the Northeast US. The GFS is likely shearing out the wave underneath tropospheric polar vortex swing south over Hudson Bay. So prefer more amplified NAM, GGEM, ECMWF solutions with precipitation spreading northward late this afternoon and evening, under the right entrance region of a strong upper-level jet over Northern NY/New England.
Temperatures will cold enough aloft for snowfall. But as high pressure departs into Atlantic, winds will becoming more east-southeast. This may create some boundary level warmth for a mix of rain and snow at the start for coastal areas. But as the low moves offshore, more north-northeasterly winds with colder air, allow for change over to all snow before ending. The question on when this changeover will happen. If more low to mid-level frontogenesis occurs, moderate to heavy snowfall rates and dynamic cooling will support a faster changeover to snow. This solution has the most support from the 3km NAM, HRRR and RGEM/HRDPS, along or just NW the I-95 corridor, including parts of NYC and PHL.
At this time, we anticipate 3″-6″ for many areas, especially along the I-95 corridor and about 50 miles NW. There is potential for 6″+ snowfall, with the best chance, just inland or northwest of the I-95 corridor away from more marine influence. However, amounts may start lower over the northwestern most areas of Northwest NJ and the Lower Hudson Valley with less banding and precipitation, farther away from the coastal front and CCB/deformation zone behind this low. Lower snowfall totals are also likely with more mixing and temperatures above freezing along the immediate shores of Long Island and New Jersey.