NY NJ PA Weather Forecasts

Thursday Snow Is All About Location, And Some Will NOT Like It

7:11 AM

The latest model guidance this morning basically is describing what I posted last night.  The surface low pressure moves over southern Pennsyvlania through southern New Jersey and then begins to intensify off the New Jersey coast.  What would like drive those living in Philadelphia and southeastern Pennsylvania nuts is the forecasted QPF on the NAM, GFS, and ensemble guidance literally jumps right over Philadelphia and dive bombs right into northern, central New Jersey and the New York City area.  A bit comical if you still have a sense of humor about these sorts of things.  Well, at least I had a good laugh.

The reason for this portrayal of the precipitation shield is because the low pressure system will be weakening over the Appalachian Mountains and then intensifying along the coast.  In the meantime, this produces a dry slow effect over southeastern Pennsylvania. 

I think the guidance is a bit extreme here, but the idea of keeps Philadelphia and points south below an inch of snow as is forecasted seems reasonable to be at this point given the development and speed of the low pressure system.

What is also clear is that someone from northeastern New Jersey (basically central Monmouth County on northward), New York City, Long Island, and southern Connecticut is going to get a surprising amount of snow tomorrow morning as this low pressure system cranks up.  Right  now, the average of all the guidance suggest that the southern half of Long Island through the southern portion of New York City and coastal Monmouth County will have a small yet intense band of snow developing right over them.  The QPF on most model guidance produce around 0.25″ of precipitation over this location, which when combined with the cold temperatures produces a snowfall amount of around 6  inches of snow. 

This heavy band of snow is produced by strong mesoscale forcing directly related to the intensification of the low pressure system.  This means that there is a good chance that the placement of this band of snow is highly dependent on the location and time of intensification of the coastal  low.  So this band could easily set up over Connecticut, eastern Long Island, or even out over the ocean, impacting fishing boats and fish alike.  Right now, this is basically an unknown variable and will need to be NOW-cast.  What is known is that tomorrow’s rush hour for the New York City metro is not going to be fun. 

The following is my snow map and on going forecast, which has not changed.

Description:

Purple:  This area covers coastal Connecticut, all of Long Island, the immediate New York City metro, and coastal central New Jersey.  Snowfall accumulations of 3 to 6 inches are expected with locally higher amounts.  The idea of the forecast is that on Thursday morning, the low pressure system will begin to quickly intensify.  Low and mid level forcing is focused over these locastions to the north and west of the developing low pressure system, which will enhance precipitation in these areas.  There are some indications that a small area of convective precipitation in the coma head of the developing low pressure system may impact this location as well, which may have the potential for slightly higher snowfall totals. 

Blue:  This area covers much of the rest of the forecast area expect the central Hudson Valley and Philadelphia on south.  In this area, the low pressure system will either have not matured enough, with liquid precipitation amounts only supporting a 1 to 3 inch accumulation over these locations.  Later on Thursday morning, parts of south-central New Jersey, the southern Hudson Valley, and northern Connecticut will be just outside the area of best lifting, with snowfall amounts ranging from 1 to 3 inches.

Light Blue:  The track of the low pressure system puts both of these areas in a region of limited lifting and moisture availablity.  For Philadelphia on south including southern New Jersey, the track of the low pressure system will be right over this region with the best lifting to the north.  Although scattered snow showers are expected, only a dusting  up to an inch of snowfall is expected in this location.

Further to the north, over the central Hudson Valley and near Albany, the lifting and moisture is just too far to the south to produce much of anything but a few snow showers and possibly a dusting.  

Bust Potential:  There are several key elements that would change this forecast.  One being that the low pressure system does not intensify on Thursday morning, which will lead to the entire forecast area only getting 1 to 3 inches save Philadelphia on south where accumulation amounts wouldn’t change much anyway. 

Another bust potential is the storm track.  If there is a shift in either north or south, the best area for dynamics will shift along with it.

A third bust potential is the low pressure moves too fast for the intensification to matter, thus limiting snowfall amounts. 

There are NO concerns about precipitation type with this clipper.   

The best time period for moderate to heavy snowfall will be from 4 AM through 10 AM Thursday.

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