New Jersey’s first blockbuster winter storm is on the doorstep, with heavy snow, strong winds and coastal flooding expected over the weekend. Over a foot of snow is anticipated for a large portion of the state, but strong winds, high seas and storm surge will make coastal and bay flooding an important and dangerous part of this storm’s story as well.
Some subtle shifts in the development of our winter storm are making for some important changes to the forecast. An upper level low over the Deep South will drive much of the dynamics and somewhat the path of our surface low. This upper level feature has driven a bit further south, and has “cut off” from the rest of the west to east atmospheric flow earlier than expected. As a result, our surface low may not climb as far north up the eastern seaboard as I anticipated over the last couple of days. The result is a trimming back of snowfall totals for northern New Jersey. The precipitation shield will be very banding dependent. One town will be getting heavy snow, while their neighbors a few miles away see much less. These factors — the banded nature and questionable northern progression of the precipitation — will result in a very sharp snowfall gradient on the northern edge of the accumulation area. This makes the forecast incredibly difficult as a distance of 25 miles, Sussex to Morris County, for example, could spell the difference between two inches and 10. Nailing down the exact placement of heavy snow versus almost no snow won’t be possible until the event is well underway.
None of this takes away from the significant impact that will be felt across most of the state. Beginning Friday night, snow will slowly overspread southern New Jersey, and then creep across the northern half of the state as daybreak approaches. Sussex, Passaic and Bergen counties may not see snow begin until mid-morning as the precipitation shield struggles to progress here at first. Winds will quickly strengthen overnight Friday, especially for the coast and Cape May. By Saturday morning, sustained winds of 30 to 40 mph will have been howling for hours over coastal areas, pressing ocean water against the coastline and into the bays. The full moon maximizes the tidal cycle, so even without this storm tides would be above average. Twenty-four hours of strong, sustained easterly winds will create a storm surge of three to four feet on top of the lunar-enhanced high tide, so Saturday morning and evening, and Sunday morning between 7 and 8 o’clock will bring the strongest threat of flooding to coastal areas. Coupled with the possibility of heavy snow and strong winds, power failures are a strong concern. Coastal residents should be treating this as seriously as they would a direct landfall from a strong tropical storm.
Elsewhere across New Jersey, I am less concerned about winds, although gusts to 30 or 40 mph are possible occasionally, which coupled with heavy snow would drop visibility to near zero. Heavy snow falls across central and interior southern New Jersey on Saturday, with lighter snowfall spreading across the northern third of the state through the afternoon. Precipitation intensity and winds will begin to subside northwest to southeast beginning around midnight on Saturday. Snow may linger along the shore through mid-morning Sunday, and the winds will remain strong here for the aforementioned third straight high tide cycle.
So what remains to be resolved, and what could go wrong? It is important to remember that computer modeling depends on an approximation of many intricate, small and important physical processes that are interdependent on one another. Subtle changes on this system’s northward progression, which is still not agreed upon and resolved by modeling, will have major changes in the practical weather experienced by northern parts of the forecast area. Someone will receive very little snowfall relative to another location a few miles south. That tight gradient could be realized over southern New York, northern New Jersey or as far south as the Route 78 corridor including New York City. In far southern and coastal New Jersey, a subtle shift north will introduce more rain and mixing issues, cutting back on snow totals.
We are entering the time period where the short-term, rapid updating “mesoscale” models come into their wheelhouse. This should help reach some conclusions as to the northern gradient, the possibility of mixing and the most likely location of the heaviest banded precipitation. For now, all residents should prepare for the most significant snowfall of the last two winters and coastal residents should prepare for a top 10 flooding event in New Jersey history.