1:00 PM | ***Accumulating snow later tomorrow evening into early Saturday morning in the DC-to-Philly-to-NYC corridor…snowfall estimates by metro region in posting…***

A key factor during the early weekend snow event in the Mid-Atlantic region will be a strong and strengthening upper-level jet streak that will enhance upward motion at the surface and help to produce accumulating snow. Map courtesy NOAA, tropicaltidbits.com

Overview

A low pressure system will slide to our north later today and pull a strong cold front through the region which will usher in a reinforcing cold and dry air mass to end the work week. The passage of the front this evening will likely be accompanied by gusty winds, snow showers, and perhaps even a heavier snow squall or two across much of upstate Pennsylvania and New York State. The cold front will then will set up shop on Friday in the southern Mid-Atlantic region and low pressure will slide along the frontal boundary zone resulting in accumulating snow all along the DC-to-Philly-to-NYC corridor from later tomorrow evening into early Saturday. While there will be limited moisture available to this system and it’ll be a fast-mover, a strong and strengthening upper-level jet streak will enhance upward motion in the DC-to-Philly-to-NYC corridor and the result will be a few inches of snow by early Saturday morning. Contrary to the storm earlier this week, this upcoming system will encounter an established cold, dry air mass on its front side meaning snow will likely be the dominate precipitation type all the way down to the DC metro region.

Details

Fast-moving low pressure will push to our north later today and drag a strong cold front through the Mid-Atlantic region with gusty snow showers and perhaps even a heavier snow squall in some portions of upstate PA and NY State. The passage of the front will usher in a reinforcing cold, dry air mass for Friday with high pressure building into the area. This front will stall out across the southern Mid-Atlantic region and the next low pressure system will push along the frontal boundary zone later tomorrow and Friday night. As a result of the influx of reinforcing cold air, the arrival of moisture on Friday night is likely to result in snow being the dominant precipitation type…even down to the DC metro region.

Low pressure will be located off the southern Mid-Atlantic coastline by early Saturday morning with accumulating snow likely in the DC-to-Philly-to-NYC corridor. Map courtesy NOAA, tropicaltidbits.com

While there are limiting factors for snow accumulations with this approaching low pressure system, there are also a couple of important favorable factors. On the limiting side, this approaching low pressure system will be rather weak, a fast-mover (only about a 6-hour period of snow) , and it’ll have limited amounts of available moisture. However, I believe a few inches of snow is still possible in much of the I-95 corridor as a result of a couple of favorable factors. First, there will be a strong and strengthening jet streak in the upper part of the atmosphere that will generate strong upward motion at the surface adding to the chance for accumulating snow. Second, the incoming cold, dry air mass will create an atmosphere that allows for a high “snow-to-rain” ratios (i.e., greater than the normal 10:1) and this suggests even a small amount of “liquid equivalent” precipitation can produce at least a few inches of snow which would be on the light and fluffy side…not like the heavy, wet snow of earlier in the week.

The circled area on this forecast map for late tomorrow night highlights the region with strong upward motion produced by a powerful upper-level jet streak. Map courtesy NOAA, Pivotal Weather

Snowfall estimates are 2-4 inches in the DC and Philly metro regions from later Friday evening into early Saturday morning with isolated higher amounts likely…1-3 inches across the NYC metro area…this will be a quick-moving system with about a 6-8 hour period of snow (light and fluffy texture).

Colder-than-normal air will follow the early weekend snow event in the Mid-Atlantic region with below-normal temperatures on Saturday night and Sunday. Map courtesy NOAA, tropicaltidbits.com

Following the departure of the low, cold, breezy and dry conditions will dominate for the remainder of the weekend as high pressure pushes in from the west and the departing low pressure intensifies off to our east. This high pressure then pushes to our east early next week which will begin a warming trend as a low-level southwesterly flow of air should develop in the Mid-Atlantic region.

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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