2:45 PM | ****Rain early tonight mixes with sleet late...changes to accumulating snow by early tomorrow in much of DC-to-Philly-to-NYC corridor…impact on AM commute in many spots…a dynamic storm****

The “dark blue” area seen in this forecast map by the 12Z NAM indicates “heavy snowfall” and it can certainly wreak havoc on road conditions in a hurry despite the relatively warm ground temperatures at the onset of the storm. Map courtesy NOAA, tropicaltidbits.com

Overview

A very dynamic storm system is headed to the Mid-Atlantic region and Northeast US and it is going to produce sleet and significant accumulating snow in many sections with an impact on at least part of the Tuesday morning commute…and “thundersnow” is even on the table. There is no real cold air established for the onset of the approaching storm so precipitation arrives this evening in the form of rain all along the immediate DC-to-Philly-to-NYC corridor. However, as the surface low intensifies off the Mid-Atlantic coastline early Tuesday, colder air will get quickly wrapped into the system from the north and west, winds will intensify, and there will be a changeover from rain-to-sleet-to-snow.  Significant accumulations of snow are likely on Tuesday morning across Pennsylvania, central/northern New Jersey, and in the New York City metro region. There can even be some accumulations early tomorrow across northern Maryland and all the way into the northern and western suburbs of Washington, D.C.

With such a dynamic storm, “thundersnow” will be a possibility on Tuesday morning in some sections of the Mid-Atlantic region and this is usually correlated with heavy precipitation bands. Map courtesy NOAA, tropicaltidbits.com

Details

A dynamic storm system is headed to the Mid-Atlantic region and Northeast US and those dynamics can result in intense snow and/or sleet bands in some areas along the DC-to-Philly-to-NYC corridor…and, unfortunately, just in time for at least the latter part of the AM commute. In fact, given such strong support in the upper atmosphere, there can be “thundersnow” during this storm in some spots and that usually is correlated with bands of heavy precipitation. Mild air precedes the arrival of the storm with highs later today well up in the 40’s in most of the I-95 corridor, but colder air is poised just to the north and west and will get quickly wrapped into the system early tomorrow as the surface low intensifies off the Mid-Atlantic coastline. Low pressure is pushing to the northeast today out of the Tennessee Valley and it’ll head towards southern West Virginia by later tonight and then transfer to an intensifying coastal low early Tuesday just off the Delmarva Peninsula.

Accumulating snow in the Mid-Atlantic region on Tuesday can extend all the way down to northern Maryland and N/W suburbs of Washington, D.C. there can be an important impact on driving conditions in much of the DC-to-Philly-to-NYC corridor. Map courtesy NOAA, Pivotal Weather

Temperatures early tomorrow morning will be only moderately cold along the DC-to-Philly-to-NYC corridor - likely within a few degrees of the freezing mark - and ground temperatures are relatively mild after the recent warmer-than-normal weather. However, problems can quickly develop on the roads for the morning commute as the result of a couple of factors: (1) a period of sleet at the beginning of the transition phase which will put down a layer of ice and (2) a burst of heavy snow is quite possible which can cool off roadways rather quickly. The timing of the changeover from rain-to-sleet-to-snow is 5-8 AM along the DC-to-Philly-to-NYC corridor and the snow should wind down by mid-day; however, strong winds will remain through the afternoon (gusting up to 40 mph or so).

This will be quite a dynamic storm system with the support of a lot of “vorticity” aloft (i.e., spin in the atmosphere) and this enhanced upward motion can result in mesoscale bands of heavy snow on Tuesday morning and perhaps even isolated “thundersnow”. Map courtesy NOAA, tropicaltidbits.com

A couple other notes to mention…winds will increase in intensity during this storm system and become a big factor. Indeed, given the fact that the snow is likely to be of the “wet” variety  and it’ll follow a lengthy period of rain, there can be tree limbs that are “weighed down”…in other words, isolated power outages are on the table. Also, given a lengthy fetch of onshore winds during the storm, coastal flooding is certainly a real threat late tonight and Tuesday in such areas as coastal New Jersey, coastal Delmarva, and in the Maryland Counties just to the east of DC.

Updated snowfall estimates are as follows for the I-95 corridor:

DC:                 ranging from a coating just to the south and east of the immediate metro region to as much as 2-3 inches in some of the northern and western suburbs

Philly:             3-6 inches and isolated higher amounts are possible

NYC:               4-8 inches and isolated higher amounts are possible

Stay tuned…this is a dynamic storm.

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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