12:30 PM | ***Major ocean storm to bring us rain and it has the potential to produce damaging winds, power outages and accumulating snow***
Very strong high-latitude blocking is now forming in the upper part of the atmosphere over Greenland and northern Canada and this will become a key factor in the unfolding weather scenario for the Mid-Atlantic region. A major ocean storm will form by later Friday and it will become a slow-mover as a result of the blocking pattern to the north; consequently, it’ll impact the region for an extended period of time. This powerful storm will initially generate soaking rainfall for the DC-to-Philly-NYC corridor, but then as rapid intensification unfolds and colder air gets drawn in, the potential will exist for damaging winds and heavy, wet accumulating snow as we close out the work week.
Strong surface low pressure will head towards the Ohio Valley on Thursday, but it will soon thereafter become overshadowed by rapidly intensifying low pressure over the western Atlantic Ocean. In fact, it looks like this ocean storm will undergo a dramatic strengthening of nearly 24 millibars in a 24 hour period between tomorrow night and Friday night – something we haven’t seen since the so-called “bomb cyclone” of earlier this year. The ocean storm will first try the rather typical track up along the Northeast US coastline, but it will run into an "atmospheric brick wall" and be forced to push southward and perhaps even into an unusual looping fashion. Rain will overspread the I-95 corridor on Thursday and winds will pick up early tomorrow night as the strengthening process begins for the developing ocean storm.
By later tomorrow night and early Friday, winds will become a major factor with this storm. As the storm rapidly intensifies over the western Atlantic Ocean, the pressure gradient will tighten and winds will strengthen dramatically. Wind gusts past 50 mph are quite likely in the immediate DC-to-Philly-to-NYC corridor from Friday into Friday night and even higher levels may be reached at the coastline. Downed trees and power outages are a growing concern given these expected high wind gusts and the wet grounds from recent rain events which can weaken the root system. Strong winds for an extended period of time will also likely result in the buildup of significant waves in the western Atlantic Ocean and this will increase chances for beach erosion in some coastal sections.
In terms of snow, the track and intensity of the upper-level low over the next couple of days will be a key to pinpointing the areas with the best chances for accumulating snow from this unfolding major ocean storm. Initially, there is little in the way of cold air for this system to work with; however, as the storm rapidly intensifies, it will actually be able to generate its own cold air. In areas near and just to the north of the track of the upper-level low, there will be strong upward motion and this “dynamics” in the upper atmosphere will act to cool the lower atmosphere and increase chances for accumulating snow later Friday and Friday night. Small-scale (a.k.a., mesoscale) bands of snow may form on Friday with the expected strong dynamics resulting in variable snowfall rates over a given region at a particular time.
The 12Z NAM forecast map at 500 mb on Friday morning places the upper-level low over the Delmarva Peninsula/southern New Jersey region and the predicted track and strength of this feature would favor wind-whipped accumulating snow in areas like eastern PA, New Jersey and southern New York including the Philly and NYC metro regions. Elevation will also likely play a key role in snowfall during this upcoming event. Snow will be favored in those higher-elevation locations and mountainous areas like the Poconos in PA and the Catskills in NY could receive 6-12 inches of snow from this upcoming storm.
One final note, as part of the overall pattern change across the Northern Hemisphere in recent days, there has been extreme cold in much of Europe and accumulating snow in unusual places. Rome, Italy, for example, had about 4 inches of snow which was the most there in several years and in Naples, Italy where they had the biggest snowfall in 50 years. Indeed, a massive blizzard is likely to hit the United Kingdom over the next couple of days and this stormy pattern is likely to continue through the first half of March - not only across Europe, but also here in the US. In fact, we may have to deal with another storm near the US east coast in the March 7th/8th time frame and then another one around March 11th or so.
Stay tuned…winter is not going to give up without a fight.
Meteorologist Paul Dorian
Extended video discussion on the upcoming major storm: