11:30 AM | ***New year brings about a new weather pattern…accumulating snow on Monday in parts of Mid-Atlantic with biggest threat zone DC-to-Delmarva-to-southern NJ***
Paul Dorian
The strong disturbance aloft in the Southeast US will help to spawn a storm downstream that will impact parts of the Mid-Atlantic region with accumulating snow late tonight/early Monday. Map courtesy NOAA, tropicaltidbits.com
Overview
The month of December ended with well above normal temperatures throughout the Mid-Atlantic region and the big cities of DC, Philly and NYC had no measurable snow. The new month and new year has coincided with a pattern change in the atmosphere that will bring winter weather to the eastern states including the strong likelihood for significant accumulating snow in parts of the Mid-Atlantic region with a focus on the zone from DC-to-Delmarva-to-southern New Jersey. A second winter storm is possible late this week that could result in more accumulating snow for the Mid-Atlantic region on Thursday night and Friday.
Much colder air has pushed across the Upper Midwest yesterday and today and it will arrive in the Mid-Atlantic region in the overnight hours - in a modified form - at the same time low pressure pushes to the coastline. Map courtesy NOAA, tropicaltidbits.com
Details
Today will be another unusually mild day in the Mid-Atlantic region, but big changes are on the way. There has been persistent cold air bottled up in Alaska in recent weeks and it has been oozing to the south and east in recent days. In fact, temperatures this morning in Minnesota are as low as 30 degrees below zero and single digits are common in Wisconsin (probably near 10 degrees early tonight for the Packers/Vikings game in Green Bay). Some of this much colder air is headed to the Mid-Atlantic albeit in a modified form compared to the Upper Midwest.
A strong cold front will push through later today and much colder air will arrive in the Mid-Atlantic region in the overnight hours. At the same time, a very disturbance in the upper atmosphere will push through the base of a trough of low pressure in the Southeast US and take on a slightly “negative tilt”. This action will help to spawn the formation a strong low pressure system downstream. The low will push up along the cold frontal boundary zone later tonight into early Monday to a position off the Mid-Atlantic coastline by Monday morning. Precipitation will return to the I-95 corridor region later tonight and as colder air presses in from the northwest, it is likely to become snow and accumulations are likely; especially, in the zone from around DC to the Delmarva Peninsula to the southern part of New Jersey.
In terms of potential accumulations, there are a couple of limiting factors that must be considered. First, the grounds are quite warm considering the recent persistent unusually mild weather. Second, the precipitation will begin while the lower atmosphere is still above the freezing mark. However, both of these limiting factors can be overcome by the temperatures that are likely to drop to near freezing or below after the initial onset of precipitation and by the snowfall itself which can fall heavily enough to accumulate – even on the warm grounds.
There is likely to be a sharp snowfall gradient in the DC metro region with 3-6 inches on the table for the northern and western suburbs and as much as 6-10 inches possible in the District and nearby suburbs. The Philly metro region is likely to also have a sharp gradient from little to no snow in the far northwestern suburbs to perhaps as much as a couple of inches in the city of Philly and neighboring NJ communities...6-10 inches is likely at the Jersey Shore from Atlantic City-to-Cape May. The NYC metro region will be on the northwest fringes of the main snow band with little to no snow accumulations expected up there. One other note, in some of the hardest hits areas between DC and southern NJ, don’t be surprised to experience some “thunder snow” given this strong disturbance in the upper atmosphere.
A word of caution, given the expected sharp gradient in snowfall with this storm track, a minor shift to the N/W or to the S/E can have big implications on accumulations in the DC-to-Philly-to-NYC corridor from a very minor event to a major event. In other words - even this close to actual event time - this is a low confidence forecast.
Looking ahead, it stays cold on Tuesday, but then turns a bit milder on Wednesday. That mid-week warm up, however, will be brief as another cold front passes through by Thursday and that could set the stage for more snow by Thursday night and Friday as another storm could intensify near the Mid-Atlantic coastline…stay tuned.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com