12:00 PM | *****Explosive intensification with early weekend ocean storm…major impact in Northeast US and eastern Mid-Atlantic region*****
Paul Dorian
Strong and still deepening low pressure will located off the Mid-Atlantic coastline by early Saturday morning as depicted here by the 12Z GEM computer forecast model. 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 late 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”. Some snow is likely to break out during the day on Friday across the Mid-Atlantic and Northeast US as an Arctic cold frontal system arrives and small accumulations are even possible. The main event by the rapidly intensifying ocean storm will take place on Friday night and Saturday. Very cold air will follow on its heels later this weekend all the way down to the southern part of Florida where Miami could see lows in the 30’s for the first time since 2010.
Explosive intensification of low pressure off the east coast will reduce its central pressure by 37 millibars between mid-day Friday and mid-day Saturday as depicted by the 12Z GEM 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
Arctic air remains firmly in place today in the northeastern quadrant of the nation and there will be plenty of sunshine. Clouds will increase tonight and then it’ll become overcast on Friday with the good chance that snow breaks out during the day across portions of the Mid-Atlantic and Northeast US as a cold frontal system drops into the area. The snow on Friday can even result in small accumulations by later in the day - all ahead of the main event that comes Friday night and Saturday. The cold front will end up getting absorbed into the overall circulation of the developing ocean storm.
A deep upper-level low as depicted here by the 12Z GEM 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. Map courtesy NOAA, tropicaltidbits.com
Around mid-day on Friday, relatively weak surface low pressure will develop over the southwestern Atlantic Ocean. It is at this time that many ingredients will start coming together that will allow for an explosive intensification of this low 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 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.
Very cold and dry air will be situated across the eastern states on Saturday and this will result in high “snow-to-liquid” ratios at inland locations. 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 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, two things to note, this will be one of those storms where higher amounts 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 a small shift in the storm track and/or timing of the rapid intensification could have a big impact on snowfall amounts in a particular area…so stay tuned, still a very volatile situation.
Snowfall estimates:
Philly metro: 3-8 inches with the higher amounts in that range to the south and east and lesser amounts to the north and west.
DC metro: 1-5 inches with the higher amounts in that range to the south and east and lesser amounts to the north and west.
NYC, New Jersey, southern half of Delmarva Peninsula: 8-16 inches with even higher amounts possible along coastal sections…an all-out blizzard in this region.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com
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