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12:25 PM | ***Accumulating snow late Wednesday night/early Thursday...early estimates for DC, Philly, NYC...threat for significant snow is on the rise***

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Weather forecasting and analysis, space and historic events, climate information

12:25 PM | ***Accumulating snow late Wednesday night/early Thursday...early estimates for DC, Philly, NYC...threat for significant snow is on the rise***

Paul Dorian

 12Z NAM 3-km surface forecast map for 7am Thursday (snow in blue); map courtesy tropicaltidbits.com, NOAA/EMC

12Z NAM 3-km surface forecast map for 7am Thursday (snow in blue); map courtesy tropicaltidbits.com, NOAA/EMC

The threat for a snowstorm is increasing from Philly to Boston and accumulating snow is likely down to the DC metro region.  The weather pattern will be very active in the I-95 corridor over the next 48 hours ranging dramatically from near record warmth in some spots to accumulating snow.  It’ll be much warmer today in the southern Mid-Atlantic region and those unusually warm conditions will extend on Wednesday into the rest of the Mid-Atlantic region and there will be some shower activity to go along with the warm up.   Colder air will then push into the region tomorrow evening at the same time low pressure forms in the Mid-Atlantic region.  Rain is likely for awhile tomorrow night, but then as colder air moves in a changeover to snow will take place from northwest-to-southeast.  By early Thursday morning, intensifying low pressure will be just off the Mid-Atlantic coastline and the snow could be falling heavily; especially, in places north of the PA/MD border.  When all is said and done, this is likely to be the heaviest snowfall this season in many areas north of the PA/MD border with several inches of snow on the table.  This storm will likely head all the way up along the coastline dumping accumulating snow on eastern New England as well.

 24-hour change in upper-level energy forecast map by the GFS showing a stronger system in its latest run; maps courtesy tropicaltidbits.com, NOAA/EMC

24-hour change in upper-level energy forecast map by the GFS showing a stronger system in its latest run; maps courtesy tropicaltidbits.com, NOAA/EMC

Models are coming into general agreement on the formation of low pressure along a cold frontal boundary zone by late Wednesday and this system is likely to move to a position just off the Mid-Atlantic coastline by early Thursday morning.  Upper-level energy will drop into the middle of the country by tomorrow and this should be the catalyst for the formation of low pressure in the eastern states just at the same time colder air pushes in from the northwest after an unusually warm spell.  As event time approaches, the all-important upper-level energy is looking stronger and stronger as indicated by the difference maps between yesterday’s 12Z GFS model run (left) and today’s (right).  Precipitation from this developing low pressure system is likely to arrive in the I-95 corridor during the Wednesday evening hours - likely in the form of plain rain - but as colder air works its way into the area a changeover to snow is quite likely – occurring first in the northern and western suburbs.  

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

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

As the storm reaches the relatively warm waters just off the New Jersey coastline early Thursday morning, there could be a “sweet zone” time period where it is just cold enough for snow and the precipitation is falling heavily (i.e., as rapidly accumulating snow).  Today’s 12Z high-resolution NAM model run and the 12Z GFS show this “sweet zone” possibility in their latest forecast maps for early Thursday morning with heavy snow shown (in dark blue) across much of the area north of the PA/MD border.  Travel is looking quite problematic on Thursday morning along the I-95 corridor all the way from DC-to-Boston.

A few other thoughts…this snowfall is quite likely going to end up clinging to tree branches and bushes as the rainfall at the onset will wet everything and this will allow the snow to cling quite well.  While this potential scenario could lead to a very pretty snowfall, it could also lead to enough extra weight on branches that could be just too much for them – of course, all depending on how much snow actually falls. 

Preliminary snowfall estimates:
DC metro region: coating to 3 inches
Philly and NYC metro regions: 3-6 inches
The higher amounts in these snowfall ranges will likely occur in the northern and western suburbs where the changeover will first take place. 

Stay tuned, still details to iron out and if the strengthening trend for the upper-level support continues, snowfall amounts may have to be increased up and down the I-95 corridor.  

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com 

Video discussion: