Major coastal storm to impact the area Thursday

Forecast models have converged on the eventual development and track of a significant coastal storm, which will form on Wednesday and impact the area from later Wednesday through Thursday. Although there is still some variance among model solutions regarding the exact details of the system, a decreasing envelope of potential solutions has increased confidence in the eventual impacts in our area. A strong storm system will develop off the Carolina coast on Wednesday as a result of a powerful mid and upper level trough and shortwave. Phasing disturbances aloft will eventually reach the East Coast and help to develop a strong low pressure system, which will push north and eventually northeastward from the Mid Atlantic coast to the shores of New England.

As this occurs, significant precipitation will surge northward from the Mid Atlantic into New England. Falling as snow initially, precipitation type will become a tough forecast during the height of the storm. Forecast models indicate some mid level and surface warming after an initial burst of heavy snow, which could lead to a changeover to sleet and rain along the area coasts and Long Island. However, as the surface low strengthens and the upper level low nears, temperatures are expected to drop again and precipitation will likely change back over to snow. Accordingly, confidence is rising in a major winter storm throughout the area — with the potentially highest snowfall totals from parts of interior Central New Jersey into Northern NJ and New York City and interior Connecticut.

NAM model showing a significant coastal storm impacting the area on Thursday with heavy snow in much of NJ, NY and CT.

NAM model showing a significant coastal storm impacting the area on Thursday with heavy snow in much of NJ, NY and CT.

How is the storm forming?

A major coastal storm will form as a result of a very intricate atmospheric process. A southern stream disturbance over the Southeast states will shift eastward by late Tuesday. But more importantly, an energetic northern stream disturbance will slide southeastward and phase with the aforementioned southern stream energy. The result will be a powerful mid level shortwave and mid/upper level trough, which will help the development of a strengthening surface low pressure system near the Carolina coast.

As the mid level trough feels the effects of the Western Atlantic ridge, it will amplify northward up the East Coast. The surface low, as a result, will strengthen rapidly and turn northward (maybe even northwest for a time) towards the Mid Atlantic coast. As this occurs, a second system right on the heels of this one — over the Great Lakes — will begin to push on the pattern a bit, forcing this system to remain somewhat progressive and move northeast instead of wrapping up and coming inland along the coasts.

NAM model showing the evolution of vorticity aloft, with a phased upper level trough over the Southeast States on Thursday.

NAM model showing the evolution of vorticity aloft, with a phased upper level trough over the Southeast States on Thursday.

What are the expected impacts?

Snow: Moderate snowfall is expected throughout the area, with the potential for higher amounts if banding trends stronger or impacts the area for prolonged periods of time. Confidence in higher amounts is currently low enough so that we will not include them on our official snowfall forecast. Instead, we will include a high likelihood of moderate snowfall amounts (5-9″) throughout the area. Near the coast, lower amounts are expected as a result of warming at both the mid levels of the atmosphere and the surface, which will allow precipitation to change to sleet and rain during part of the storm and hold down snowfall totals.

The precipitation-type forecast remains most challenging. Although all areas will begin as snow (and heavy snow, at that) forecast models are insistent on the development of mid level and surface warming which will push northward with time. This makes sense given the strong warm air advection occurring initially as the system pushes rapidly northward. So our confidence in precipitation changing to rain in Southeast NJ, The NJ Shore, and Long Island is rather high. That being said, it remains to be seen how far north and west this changeover line gets. Heavy precipitation could also help — with dynamic/evaporational cooling — allowing precipitation to remain a heavy, wet snow in areas which are borderline.

Storm Total Snowfall forecast from our meteorologists. Legend bottom right.

Storm Total Snowfall forecast from our meteorologists. Legend bottom right.

With these concerns in mind, our snowfall forecast currently calls for 3-6″ of snow across the Southeast part of New Jersey and along the shore including Southern Long Island. Farther northwest we are expecting 6-9″ of snow over a broad area. It is important to note that there will likely be areas receiving 9-12″ of snow with the potential for more. But we do not have enough confidence to nail down that area just yet.

Wind: Wind forecasts with this coastal system are not currently forecast to reach a dangerous level. That being said, the storm system is expected to take a track relatively close to the area shores. As is always the case with a strengthening low pressure tracking near the coast, gusty winds are expected. And this system will be no different. Wind forecasts along the beaches of New Jersey currently call for gusts from 25 to 30 miles per hour. But with the system trending a bit stronger on the latest model runs, the potential for wind gusts over 40 miles per hour cannot be ruled out.

If you will be near the shore during this storm system, keep an eye on wind forecasts. Currently, this looks like a “classic” windy coastal storm. But a track closer to the coast will increase wind impacts.

Coastal Flooding: The strong coastal storm system nearing the area in conjunction with both high tides on Thursday could lead to moderate coastal flooding. An easterly wind direction early on while the storm is tucked in near the Mid Atlantic coast to our south will not help. We are currently expecting moderate coastal flooding along the NJ Shores as well as the Delaware and Raritan Bays.

The coastal flooding impacts will obviously peak near both high tides on Thursday, but will become noticeable as soon as the system begins its move up the east coast Thursday morning. If your area is typically impacted by coastal flooding, we suggest taking precautions now.

Can you give us information on timing?

Steady precipitation is expected to begin during the late evening hours on Wednesday into the early morning hours on Thursday in New York City, but a bit earlier than that across parts of Southern and Central New Jersey. Precipitation at that time will begin as snow throughout the area. A band of heavy snow is expected to surge northward with time, through New Jersey and into New York City by the early to mid morning hours on Thursday. The morning commute on Thursday looks to be a mess throughout a vast majority of the area.

By later Thursday morning, precipitation will begin to mix with sleet and rain across Southeast NJ. This mixing area will slowly shift northward along the shore. Areas that remain snow will see very heavy snow late Thursday morning into the afternoon with continued accumulations. The rain/snow line will continue shifting northward towards Long Island on Thursday, with heavy snow continuing just northwest of that thermal boundary.

As the coastal low nears the area, cold air will begin to funnel in once again — and so a transition back to snow is eventually expected before precipitation ends. The heaviest/steadiest precipitation will wrap up from west to east late Thursday around dinner-time into the evening hours.

Stay tuned over the next day or so for continued updates and refreshing of products including new snowfall maps, timing information and hazards briefings.