Mid AM Zone Update: Impactful snow likely Friday

A few weeks ago we discussed the likelihood that winter would return in the early to middle part of the month of March. Well, here we are! High latitude blocking developed several days ago and is continuing to strengthen this week, moving westward from Greenland into Canada. This blocking is dislodging cold air, which otherwise would be bottled up in the Arctic region, further south.

As this occurs, a very notable temperature gradient will develop from the eastern Ohio Valley into the Northeast states. Forecast models agree that a disturbance in the atmosphere’s mid levels will shift through the aforementioned area from late Thursday Night into Friday, with a low pressure system developing along the thermal gradient and moving from the Mid Atlantic states off the coast to a position south of Long Island.

Low pressure development along a thermal gradient is always a critical, and highly tricky, part to a forecast. Thermal gradients are important for several reasons, but mainly because they serve as a harbinger for the development of frontogenesis. Frontogenesis is the process of these gradients tightening and strengthening in multiple levels of the atmosphere. As this occurs, lift improves, and precipitation becomes more intense.

So, with a notable thermal gradient modeled, we are looking at the potential for frontogenesis along and near the gradient which could produce at least moderate precipitation rates. With cold air pressing southwards as the low pressure develops, this precipitation is likely to fall mostly in the form of snow. Along this “Stripe” of the thermal gradient is where we are looking at the potential for a moderate snowfall.

Latest watches, warnings, advisories from the NWS

Latest watches, warnings, advisories from the NWSM

Evolution of the event

Snow will begin to spread eastwards from the Ohio Valley into the Northeast states later tonight as the low pressure system develops. Models suggest the mid level disturbance will strengthen a bit on its movement east, allowing precipitation to become more enhanced once it reaches Pennsylvania. A low pressure system will then develop across the Mid Atlantic states. This will begin to touch off more enhanced frontogenesis and precipitation.

Here, the forecast gets a bit more tricky. Heavier snowfall rates will develop late Thursday night into Friday morning along the thermal gradient, but forecast models have waffled back and forth with this gradient quite a bit. Exactly where it sets up will determine where the heaviest snowfall falls. The most likely location is along the I-80 corridor of Pennsylvania into the I-78 Corridor of New Jersey, including parts of Southeast NY and Southwest CT.

GFS model showing snow throughout much of the area on Friday AM.

GFS model showing snow throughout much of the area on Friday AM.

Adding to the complexity is a warm boundary layer initially across Southern NJ and parts of the Mid Atlantic. While the atmospheric column will cool eventually to support snow, lower amounts are expected here with warm air initially allowing precipitation to fall as rain or wet, non-accumulating snow. These regions will likely still see light accumulations as the snow becomes more intense on Friday.

The most intense snowfall looks to occur during the mid to late morning on Friday across Eastern PA, Northern NJ, NYC and parts of SW CT. This will create significant issues with the AM Commute and we anticipate moderate to significant disruptions. While snowfall amounts will be moderate (3-6″) the timing of the event leads to concerns. We suggest leaving extra time for your travel and checking road conditions before you depart.

Wrapping up and acknowledging uncertainties 

stormtotalsnow_march92017

To summarize, we are anticipating a light to moderate snowfall event throughout the entire region from Thursday evening through Friday afternoon. Despite only light to moderate snowfall amounts, impacts to the morning commute are likely to be notable. This will be especially true from the I-80 Corridor in PA to the I-78 Corridor in NJ and a swath north of there including SE NY and SW CT as well as the NYC Metro.

Uncertainties still exist in regards to the exact placement of the temperature gradient and enhanced precipitation. Some forecast models continue to waffle with its placement, which would affect the placement of the heaviest snowfall. Movement north or south adds complexity to the forecast that will continue to be monitored.

Snowfall removal services in the mentioned corridors should prepare for activity from tonight through Friday morning. Personal/residential clients should prepare to leave extra time on the morning commute, which will be a mess. Stay tuned for further updates and details!