*****Accumulating snow, powerful winds, bitter cold…all impacts from an explosive ocean storm*****
Paul Dorian
A deep upper-level low as depicted here by the 12Z NAM model will take on a slightly “negative” axis orientation tilt by early Saturday morning enhancing upward motion in the vicinity of the surface low pressure system and back to the I-95 corridor. Map courtesy NOAA, Pivotal Weather
Overview
Many ingredients are going to come together that will allow for explosive intensification of a storm system over the western Atlantic Ocean between mid-day today and late Saturday. In fact, it appears that this low pressure system will easily surpass the requirement of a central pressure drop of at least 24 millibars in a 24-hour period to be classified as a “bomb cyclone”. Some snow is likely to break out today across the Mid-Atlantic and Northeast US and then the main event will come tonight and Saturday from this intensifying storm. Very cold air will push into the eastern states during the height of the storm on Saturday and it’ll be bitter cold tomorrow night with brutal wind chills. This Arctic blast will plunge all the way down to southern Florida and even to Cuba. Miami is likely to experience lows in the 30’s this weekend for the first time since 2010.
Explosive intensification of low pressure off the east coast will reduce its central pressure by 38 millibars between mid-day today and mid-day Saturday as depicted by the 12Z NAM model. This rapid and substantial drop in central pressure during a 24-hour period would qualify this storm to be considered a “bomb cyclone”. Maps courtesy NOAA, Pivotal Weather
Details
Snow has broken out today in portions of the Mid-Atlantic and Northeast US as an Arctic cold frontal system pushes into the northeastern quadrant of the nation. The snow can even accumulate some with temperatures generally holding nearly steady anywhere in the range of the upper 20’s to the low/mid 30’s in the DC-to-Philly-to-NYC corridor. This frontal system will end up getting absorbed into the overall circulation pattern of the developing ocean storm and the Arctic air will play a big role.
Very cold and dry air will be situated across the eastern states on Saturday and this will result in high “snow-to-liquid” ratios of 15 or 20:1 at many inland locations. Map courtesy NOAA, Pivotal Weather
By the early afternoon, relatively weak surface low pressure will develop over the southwestern Atlantic Ocean just off the southeast US coastline. It is at this time that many ingredients will start to come together that will allow for an explosive intensification of this low over the next 24 or so hours as it begins a general push to the north. These ingredients include the following:
1) two upper-level disturbances that will eventually “phase” together
2) strong jet streaks in the northern and southern branches of the jet stream and at different levels of the atmosphere
3) plenty of very cold and dry Arctic air to the north and west
4) relatively warm waters in the western Atlantic Ocean
5) deepening low pressure at mid-levels of the atmosphere that will take on a “negative” tilt in its axis orientation.
Multiple jet streaks at multiple levels of the atmosphere will play a role in the rapid intensification f this storm system. This forecast map by the 12Z NAM model shows 850 mb winds as of early Saturday will produce an influx of moisture from off the ocean back inland into a very cold and dry air mass (hence high snow ratios). Map courtesy NOAA, Pivotal Weather
The coupling of the jet streaks at lower and upper levels of the atmosphere will allow for enhanced upward motion over the western Atlantic contributing to the rapid intensification of the storm. In addition, the low-level jet will help generate an influx of moisture from the Atlantic Ocean to the coastline and to inland locations aiding in the development of heavy snow bands. The air mass across the eastern US for much of this storm will be very cold and dry and this should result in high snow-to-liquid ratios at inland locations and a drier, fluffier type of snow which would tend to be more favorable for snow accumulations compared to a heavier, wet type of snow.
As the “phasing” together process of the two upper-level disturbances unfolds, low pressure aloft will take on a “negative” tilt to its axis orientation and this too will lead to enhanced upward motion over the western Atlantic Ocean. The exact timing of the “phasing” will be critical in the overall development and impact of this storm system with a quicker than expected “phase” potentially leading to a stronger storm that is closer-in to the coast. This would likely result in an even bigger impact in the eastern part of the Mid-Atlantic region. Another factor that will play a role in the intensification process and ultimate storm track will be the relatively warm waters of the western Atlantic Ocean as this will set up a tight temperature gradient at the coastline between the cold (land) temperatures to the west and the relatively warm low-level air to the east.
In terms of snow fall estimates, a few things to note, this will be one of those storms where higher amounts tend fall to the south and east in a given metro region and lesser amounts to the north and west. In addition, there is likely to be quite a sharp gradient in snowfall accumulations meaning there can be a big difference over a distance of 25-50 miles or so and a small shift in the ultimate storm track can make a big difference in a particle location.
Snowfall estimates:
Philly metro region: 5-10 inches with the higher amounts in that range generally to the south and east and the lesser amounts to the north and west…ends by mid-day Saturday
DC metro region: 2-5 inches with the higher amounts in that range generally to the south and east and the lesser amounts to the north and west…ends on Saturday morning in far eastern areas
New York City, New Jersey, southern half of Delmarva Peninsula: 10-20 inches with even isolated higher amounts possible along coastal sections…an all-out blizzard in this region…winds down on Saturday afternoon.
New England: Providence-to-Boston-to-Portland…potentially an historic blizzard with 20-30 inches on the table along along with a prolonged period of damaging winds.
Stay tuned…still a fluid situation.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com
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