Cold temperatures continue across the region, with lows this morning ranging from near to slightly below zero in interior areas to the 10s/low 20s closer to NYC. Cloud cover will increase today as a weak, moisture starved system races eastward, producing 1-2″ of snow this evening. Colder temperatures are expected to return on Tuesday into Tuesday night, followed by the potential for a more significant storm on Thursday with the potential for widespread wet snow and rain.
Today – Tuesday: Light Snow, Then Cold
Posted above from left to right are the latest surface analysis and radar composite from WPC, and the initialized GFS 500 millibar height and vorticity from NCEP MAG, both valid at 12z (7am). A broad area of a weak low pressure is centered from Ohio into Michigan, with widespread light to moderate snow ahead of a mid level shortwave trough over Illinois and Wisconsin. With a progressive and mostly zonal flow in the upper levels, this shortwave trough will fail to significantly amplify, and will continue to race eastward, reaching PA/NY this evening. Since the best lifting for precipitation is centered ahead of shortwaves, under regions of positive vorticity advection, the snow showers over Ohio will continue to rapidly track east as well, reaching the area late this afternoon into the evening hours. Snow showers are expected to develop from west to east between at least 4-6pm, with steady light snow anticipated until at least 10pm-12am; some of the high resolution models indicate a possible brief period of moderate snow rates this evening. Given that this is a weak system, the highest snow totals are expected west of the higher elevations in central Pennsylvania, although snow totals of at least 1-2 inches are expected across the area tonight.
Following the departure of the weak system, colder temperatures will return into the region as a broad high pressure near southern Canada will expand east-southeast, reaching the region by Monday night into Wednesday with mostly sunny skies expected. Highs on Monday are expected to reach the mid-upper 20s, with highs on Tuesday in the low-mid 20s for most. The low temperatures will be significantly colder inland, however, as the positioning of the high pressure supporting light winds and little cloud cover along with a fresh snow cover are favorable factors for strong radiational cooling away from urban areas, especially on Tuesday night with the high pressure centered overhead. Lows on Monday night are expected to reach the single digits to low 10s away from NYC and the mid 10s in NYC and the coast; Tuesday night will be the coldest of the two for most, with low temperatures forecast to reach the low 10s in NYC and the immediate coast, mid 0s in the north/west suburbs into southern CT and most of Long Island, and near to below zero in NW NJ, interior SE NY and the Pine Barrens in Long Island. The cold temperatures on Tuesday night will be primarily as a result of strong radiational cooling as the cold air mass present on Monday will have mostly departed the region due to a southwesterly flow aloft, with temperatures on Wednesday warming into the mid 20s to low 30s.
Wednesday Night – Thursday: Snow, Rain Expected
0z ECM at hour 120, for 0z Friday (7pm Thursday), depicting a strong low pressure over eastern New England. This run is the strongest with the system, with snow to rain for the area, while the GFS is further east, brushing the area with light rain/snow (image credit: PSU e-Wall).
The next system to monitor is on Wednesday night into Thursday as a strong shortwave trough approaches the southeast US and attempts to become negatively tilted. The key players for this system originate in the northern Pacific, with a piece of a strong upper level low south of Alaska splitting and tracking ESE into the north central US, and a weak shortwave to its south which progresses ESE as well, entering California on Monday and reaching the southeast US by Wednesday. The southern shortwave trough then reaches the southeast US, with more signiifcant model differences emerging from there. Yesterday’s GFS runs kept this shortwave weak and flat, quickly racing offshore with no precipitation in the region, while the latest GFS runs are trending slower and stronger with this shortwave, which then interacts with the stronger northern stream shortwave which digs south towards the SE US, with the trough then becoming negatively tilted and supporting a stronger low tracking up the coast. The ECMWF is currently offering the most support to this scenario, with a low tracking right along the coast supporting a snow to rain scenario for the area, while the 6z GFS keeps most of the precipitation offshore.
While there remains uncertainty with the exact storm track and impact, an issue to consider is a marginal cold air setup, since the aforementioned southwesterly mid-upper level low that removes the cold air mass aloft on Tuesday will lead to a lack of a strong cold air supply for this time frame, with snow from this system likely to accumulate as wet snow. Such a setup would typically favor the heaviest snow staying inland of the I-95 corridor should the storm affect the area, although a marginal setup with the low positioned close enough to the coast to place the heavier precipitation near the I-95 corridor would support a snow axis centered closer to the coast. Given the setup favoring a moderately intense low pressure system which remains fairly progressive, in the scenario that the storm does affect the area with snow, the maximum high-end potential would exist for at least moderate to possibly heavy wet snow accumulations. At this time, I am siding closer to the ECM but with a slightly weaker low east of the coast, supporting a moderate wet snow to rain scenario for most of the area, although as this is still a few days away, additional changes are possible to the forecast over the next few days. While I am currently siding towards a further west low pressure with widespread precipitation over the area, the pattern over the US is not ideal for a significantly further west coastal low pressure system, and the potential remains for the precipitation to mostly stay east of the area.