Dangerous nor’easter to pound New Jersey Friday

John Cifelli, Meteorologist | February 28, 2018 | Weather
  • Long duration coastal storm to affect NJ Thursday through Saturday
  • Rain, wind, and accumulating snow to bring power outages
  • Extended stretch of onshore winds will cause moderate coastal flooding

A powerful coastal storm will wreak weather havoc across New Jersey beginning late Thursday through Saturday this weekend. This storm will impact New Jersey in many different ways, bringing threats of flooding rains, accumulating snow, coastal flooding, and possibly damaging winds. “Bombogenesis” may have been the weather flavor of the month earlier this season, but it applies again in this scenario. A benign surface low in the Ohio Valley on Thursday will rapidly deepen into a powerful coastal low southeast of Long Island 24 hours later by Friday afternoon. Blocked by a log jammed upper level wind flow pattern, the storm will sit off the coast or even retrograde westward towards New Jersey on Friday. Slowly, the storm will slide away on Saturday, taking the worst of the impacts with it. Even still, the surface wind pattern in its wake will keep water from flowing out of the bays and inlets, keeping the threat of coastal flooding high through Saturday night. Flooding during high tides will only be exacerbated by the lunar cycle. Thursday night brings a full moon.

All things considered, Thursday won’t be a bad day. We will see some sunshine in the morning, and temperatures will warm into the low 50s once again. Clouds thicken during the afternoon, and rain will begin before dark. This storm is heavily moisture-laden, thanks to a very active subtropical jet stream. In fact, you can follow the moisture plume across the Mississippi Valley all the way back to a point east of the Hawaiian Islands on a water vapor satellite loop as I write. There’s a lot of precipitation coming, that’s for sure. During the night on Thursday, the Ohio Valley surface low will transfer energy to the coastal low, rapidly developing along the coastal front draped just offshore. Low pressure loves a strong temperature gradient, and in the winter you can almost always find one this time of year between the relatively warm ocean air and the colder air across the land surface of the northeast United States. As the coastal low quickly strengthens, the column of air aloft cools sufficiently for rain to change to snow for far northern New Jersey, and possible central New Jersey as well. How quickly the coastal low strengthens, both at the surface and aloft, will dictate when the changeover happens and how much rain vs. snow ends up falling. This storm is powerful enough to “manufacture its own cold” with dynamic processes supporting snowfall when and where it falls hardest. You can see this indicated pretty clearly Wednesday night on model guidance. One such run shows central New Jersey snowing hard with surface temperatures around 30 degrees Fahrenheit Friday afternoon, while it is raining lightly at 35 to 36 degrees Fahrenheit hundreds of miles further north, along the border of New Hampshire and Vermont. It will simply come down to where this storm precipitates hardest. This also means that with snow aloft overwhelming surface warmth, that parts of New Jersey with elevation will see the quickest changeover. I expect snow totals to be very much elevation driven.

Tree damage and power outages are going to be considerable concerns regardless of what else happens. The ground is soggy and sodden, particularly in the northern half of the state. If 1 to 2 inches of rain falls and we see localized creek and river flooding, coupled with winds sustained above 25 mph, that can pull down trees rooted in already loose, wet ground. If some of that rain falls instead as heavy, wet snow, well that’s the recipe for limbs breaking and falling on wires. There really isn’t a scenario at this point where this isn’t a real risk.

Down the shore, all locations are at risk for minor to moderate flooding from Friday afternoon through Saturday. Flood waters reaching Major stage isn’t out of the question, particularly inlets and beaches with any northerly component to the direction they face the ocean. I can’t stress enough that while many will focus on when and where the changeover from rain to snow is, and how much falls, that flooding and wind damage are as big of a weather threat as snowfall with this storm. For now, I’m comfortable with the idea that rain changes to snow sometime Friday in the northern third or half of the state, and accumulates. Confidence and likelihood of plowable snow obviously increases the further north and higher in elevation you go. Although higher elevations see the changeover first, there’s a good chance that as the storm occludes and decays later Friday that heavier bands could slide over any part of New Jersey, oriented in N/S fashion. They could set up just along the coast, or over the New York City metro and its suburbs. For now, Route 80 and possibly the Route 78 corridor are likely to see several inches. Everyone, except perhaps those in extreme southern New Jersey, will have weather to worry about, one way or another on Friday.