12:30 PM | ****Ocean storm to undergo explosive intensification early this weekend…significant impact in eastern New England is quite certain…impact in Mid-Atlantic less certain****

A deep upper-level low as depicted here by the 12Z NAM model will take on a “negative” tilt by early Saturday enhancing upward motion in the vicinity of the surface low pressure system. Map courtesy NOAA, tropicaltidbits.com

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 Friday and mid-day Saturday.  In fact, it appears that this low pressure system may rather 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”.  The exact timing of the rapid intensification and the ultimate track of the storm are still somewhat unclear at this time and while a significant impact appears quite likely for eastern New England, there is a chance that at least part of the Mid-Atlantic region escapes with only a moderate or minor impact.

Explosive intensification of low pressure off the east coast will reduce its central pressure by 35 millibars between mid-day Friday 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, tropicaltidbits.com

Details

An Arctic blast arrived in the Mid-Atlantic region during the overnight hours and temperatures today will generally hold in the 20’s for afternoon highs in the DC-to-Philly-to-NYC corridor and then plunge to the 10-15 degree range for late night lows. In fact, it is likely to be cold enough in this Arctic air mass for late night temperature readings of near or below-zero across upstate Pennsylvania and interior sections of northwestern New Jersey.  After a sunny and cold day on Thursday, clouds will increase on Thursday night and then become overcast on Friday as event time approaches.

Upper-level jet streaks as depicted here by the 12Z NAM model will play an important role in the intensification of an ocean storm early this weekend. Map courtesy NOAA, tropicaltidbits.com

Around mid-day Friday, relatively weak low pressure will form over the southwestern Atlantic Ocean and snow is likely to break out across parts of the interior Mid-Atlantic.  It is at this time that many ingredients start coming together to allow for an explosive intensification of this low pressure system as it continues its push to the north off the east coast.  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 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 at some point take on a “negative” tilt in its axis orientation. 

A low-level jet as depicted here by the 12Z NAM model will play an important role in the intensification of an ocean storm early this weekend. Map courtesy NOAA, tropicaltidbits.com

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 inland locations aiding in the development of heavy snow bands.  As the “phasing” together process of the two upper-level disturbances unfolds, low pressure aloft will at some point take on a “negative” tilt to its axis orientation and this too will lead to enhanced upward motion over the western Atlantic. Other factors that will play a role in the unfolding scenario will include a very cold and dry air mass pushing into the eastern states from the north and west and the relatively warm waters of the western Atlantic Ocean. This combination will set up a tight temperature gradient at the coast (i.e., cold land temperatures to the west…relatively warm waters to the east) and this will also contribute to the intensification of the low pressure system and also play a role in its ultimate path.  One last point, the very cold and dry air mass to the north and west during this event will result in high snow-to-liquid ratios and a drier, fluffy type of snow at inland locations which would tend to increase snow accumulations compared to a heavier, wet type of snow.

One of the most important issues that remains as event time approaches is when will the “phasing” together of the upper-level systems actually take place and the difference of just a few hours could mean a foot of snow in a given spot versus a few inches. The timing of the “phasing” will be important in the ultimate track that the ocean storm ends up taking. As it stands now, the odds of a significant impact by this storm are highest across eastern New England in such cities as Providence, Boston and Portland.  There is more uncertainty in New York City, coastal New Jersey, and coastal Delmarva Peninsula where it wouldn’t take much for that zone to get in on some of the heaviest snowfall amounts. There is even more uncertainty in the corridor from DC-to-Baltimore-to-Philly as the storm could “phase” together too late for anything more than a few inches.  A quicker “phase” would allow for a stronger storm to be closer-in to the east coast resulting in a much bigger impact in the DC-to-Baltimore-to-Philly corridor and we should have more clarity on that prospect by later tomorrow…stay tuned. 

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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