11:35 AM | ***Snowstorm on the way for northern MD (near PA border), eastern PA, NJ, NY…all the way up to Boston…potential “white-out” conditions tomorrow morning in Philly, NYC***

12Z GFS surface forecast map for 7am Thursday; courtesy tropicaltidbits.com, NOAA/EMC

As a Penn Stater, let me borrow the phrase “white-out” which may very well describe the conditions for a brief time tomorrow morning in the Philly, NYC metro regions.  The threat for a significant snowstorm continues for the Northeast US from northern Maryland to Maine and there should be accumulating snow all the way down into the DC metro region late tonight and on Thursday. As upper-level energy slides towards the eastern US, low pressure will develop over central Virginia later this evening.  This low pressure area will then intensify as it heads northeastward reaching the waters off of the New Jersey coastline by early tomorrow.  From there, the storm will trek just east of the New England coastline spreading accumulating snow all the way up to the eastern seaboard of Maine.  

GFS snowfall amounts for this upcoming event have increased and expanded between last night's 00Z run (left) and this morning's 12Z run (right);  courtesy tropicaltidbits.com, NOAA/EMC

Today’s amazing warmth (record-breaking in some spots) will soon be replaced by a fresh, cold air mass following the passage of a cold frontal system (low-level NW winds already have arrived).  The transition to cold will not be immediate; however, as it is likely to take place over several hours from later this afternoon into the late evening hours at which time precipitation is likely to break out in the DC, Philly metro regions, a bit later than that in NYC.  As the cold air continues to filter in from the northwest during the overnight hours, the precipitation will transition from rain to sleet and then finally to snow.  The snow will pick up in intensity early tomorrow morning across northern Maryland (near the PA border), eastern PA, NJ and NY.  In fact, the brunt of the storm is likely to last for about a 3 or 4 hour period during tomorrow morning when the snow should fall heavily and travel conditions will be greatly impacted. Amazingly, the 12Z GFS forecast model projects snowfall rates as high as 3 or 4 inches per hour early tomorrow morning in the I-95 corridor region near Philly and southwest NJ with tremendous upward motion in the atmosphere. 

12Z NAM surface forecast map for 7am Thursday;  courtesy tropicaltidbits.com, NOAA/EMC

The snow will be of the heavy, wet variety and given the fact that it’ll rain initially, the snow will cling quite well to trees and bushes.  While this will make for a beautiful “white-out” scene tomorrow morning as the snow falls heavily and there is white everywhere, this scenario could lead to scattered power outages as the weight of the snow could become too heavy for some limbs.  As the storm intensifies, small-scale bands of precipitation will develop and this should produce quite a variation in snowfall rates and perhaps quite a variation in final accumulation amounts in a given area.  

Overview of track and position of low pressure system (upper, right) and snow accumulation factors and storm characteristics (left)

Given the expected very strong dynamics (i.e., upward motion) in the atmosphere, there may even be some isolated “thundersnow” during the brunt of the storm.  Winds will pick up in intensity as the day progresses and temperatures will stay at or below freezing in all areas north of the PA/MD border.  The snow winds down by mid-day or early afternoon across Philly and mid-to-late afternoon in the NYC metro region.   Temperatures later tomorrow night drop into the teens along the entire I-95 corridor region.

12Z GFS 1-hour precipitation amounts between 6 and 7am on Thursday morning which would result in 3 or 4 inches of snow in an hour; courtesy "true weather", NOAA/EMC

Snowfall estimates:
DC metro region:
-Coating to 2 inches in the District and points south and west,
-2-4 inches across the far northern and northeastern sections of the metro region

Philly metro region:     5-10 inches

NYC metro region:        6-12 inches  

Stay tuned, still some time for updates.

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com 

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Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com