7:45 AM

High pressure will continue to dominate much of the northern Mid Atlantic today through Sunday with scattered clouds and temperatures returning to near normal levels.  In fact, many locations along the coast will push into the lower 40′s for highs, which will aid in slowly melting the snow pack over the region.

The next storm to impact the Philadelphia and New York City metropolitan area is already taking shape over the Rockies and will move east this weekend towards the Ohio Valley by Monday morning.  Unlike previous storms, the focus of this storm will clearly be over interior locations like northeastern Pennsylvania, extreme northern New Jersey, the Hudson Valley, and interior Connecticut.  However, this storm will also have a significant impact on coastal locations due to the potential for significant flash flooding.  The combination of the melting snow pack and the heavy rain late Monday into Tuesday over much of coastal New Jersey, the New York City metropolitan area, Long Island, and southern Connecticut will lead to the potential for urban and small river flooding throughout the region.  Meanwhile, a mix of snow, sleet, and freezing rain is going to be a threat just inland over much of the Delaware River Valley through the central Hudson Valley.  Heavy snow will be a focus further north over the interior.

The coastal low is expected to take shape on Monday evening and move along the New Jersey coast on Tuesday morning before exiting south of Southern New England on Tuesday evening.  Colder temperatures will begin to work into the region on Tuesday evening, supporting a change over to snow for all locations, but only limited accumulations along the coast if any.

High pressure return for Wednesday with drier and colder conditions and a threat for much of the melted snow and left over ponding water to freeze into black ice.  Use caution on Wednesday morning!

Another storm is possible on Thursday evening as a Sub Tropical disturbance races on the heels of this exiting storm.  The development and track of this storm is very much uncertain, however another potential widespread impact is possible from this storm as the week ends.

8:39 AM

An intensifying low pressure system is moving through the Tennessee Valley this morning with heavy rain approaching southern New Jersey.  The heavy rain is expected to spread throughout the Philadelphia and New York City metropolitan area through this morning and become heavy this afternoon.

The hold of cold air is starting to give over most locations as an easterly wind is drawing warm Atlantic air into the region.  This has caused most locations to rise above freezing.  However, interior locations like northeastern Pennsylvania, northern New Jersey, the Hudson Valley, and much of Connecticut is still below normal.

By this afternoon, the low pressure system is expected to redevelop off the Delaware coast and move to the southeast of Long Island by Monday morning.  This storm track will initially support a strengthening east-northeasterly wind throughout the forecast area, causing surface temperatures to rise above freezing.  However, as the low pressure system intensifies, cold air will be pulled back towards the coastal plain, allowing 850 MB temperatures to fall.

While I expect all rain for much of the coastal plain, the forecast for the interior is become a bit more complicated.  The set up is still not optimal for significant ice nor snow accumulation.  However some guidance, especially the NAM BUFKIT data, does illustrate the potential if timing is just right for some ice and snow accumulation late tonight as the low pressure system exits.

Currently, I think the precipitation will start as a mix of snow, sleet, and freezing rain over northeastern Pennsylvania, northern New Jersey, the Hudson Valley, and interior Connecticut.  This precipitation will change over to rain as the evening wares on.  However, late tonight as the low pressure system intensifies and begins to exit, cold air will be reintroduced at 850 MB to the surface, creating a marginal environment for frozen precipitation before the precipitation ends.  The speed of which the cold aid builds back in not only at the surface but at each individual pressure level will determine the type of precipitation that will mix back in.  This situation will have to be NOW-CASTED tonight, which I plan to do as long as conditions warrant a threat.

The rest of the region can expect heavy rain this afternoon with 1 to 2 inches of rain possible.  Flash flooding of streams, small rivers, and urban locations will be possible in the heaviest downpours.

9:00 PM

The coldest day so far this winter season was experienced today with highs throughout the New York City and Philadelphia metropolitan areas in the 20′s and lower 30′s.  The stiff northwesterly winds through the day didn’t help matters, making temperatures fell like the mid to upper 10′s through the afternoon.  However, now high pressure has built into the northern Mid Atlantic far enough to force the strength of the pressure gradient and thus the gusty winds north of much of the forecast area.  Due to a lack of North Atlantic blocking at this time, the high pressure system building over the region tonight will exit quickly tomorrow afternoon with increasing clouds and a moderating air mass.

My overall thoughts from this morning have not changed for Sunday as an area of low pressure races north towards the New Jersey coastal waters from the North Carolina coast.  The low pressure system will act as more of a large warm front associated with the Arctic cold front well to the west rather than a separate extratropical cyclone.  The model guidance through today also has trended much warmer, however given the snow pack in place over northeastern Pennsylvania and the Hudson Valley, I think the models may be warming the boundary layer too fast.

The majority of the Philadelphia and New York City metropolitan area will be too warm to support anything but rain for Sunday afternoon through Monday morning.  Further north and west, the precipitation will briefly start as snow before changing over to a sleet and then freezing rain event.  The cold low level boundary layer should keep temperatures at or slightly below freezing through early Wednesday evening before the warm air winds out in these locations.  Location in the Mohawk and central Hudson Valleys will have cold air trapped , however even this air mass will eventually change over to rain as well by late on Sunday evening.

The coastal low will exit on early Monday morning with lingering showers.  High pressure will follow for much of Monday through Tuesday morning with temperatures near normal and dry conditions.

A strong Arctic front will move through on Tuesday night with yet another significant drop in temperatures.  The area of low pressure associated with this cold front will rapidly deepen into a strong upper low on Wednesday night and lead to a developing negative NAO.

I remain concerned for a potential moderate to heavy snow event for the period of next weekend.  My eyes are glued on two disturbances that will be moving around the large negative NAO block.  The first disturbance is over the northern Plains on Friday night.  This disturbance is expected to dive south towards the Mid Atlantic coast.  The next disturbance is barely visible on the GFS/ECMWF along the Gulf Coast, but that’s what makes me suspicious here.  Sub tropical disturbances have been under forecasted a great deal in terms of moisture and ability to move further north on the GFS, ECMWF, and plenty of other models.  The potential interaction of these two disturbances MAY be something to watch in the next several days.

Otherwise, a very cold regime is about to take hold.  One that will not be fast to break down with gaining support in the Pacific.  Enjoy the near normal temperatures this weekend, as a regime of below normal temperatures is about to set in.

6:52 AM

Before the usual morning forecast, I wanted to give an update on the storm raging outside this morning.  The rain/ice/snow line continues to steadily push north, however many locations have already been impacted.  Many locations have already experienced moderate to heavy snow with accumulations ranging from 2 inches to 6 inches over the interior locations.  The snow is mixing with and changing over to sleet and freezing rain.  Temperatures range from 28 to 32 degrees over the central Hudson Valley through extreme northeastern Pennsylvania.  As the warm air takes hold, theses locations will also change over to rain.  However, before the change over begins, much of northern Pennsylvania and interior New York (all of NY north of New York City) will be in  for a heck of a snow and ice event.

Meanwhile, further south heavy rain is falling.  The DBZ readings this morning are very impressive with 35 to 60 DBZ being recorded by this morning’ Doppler radar.  Expect flash flooding with this rainfall through the morning along with significantly reduced visibility.  Winds this morning range from 15 to 25 mph sustained with gusts ranging from 30 to 40 mph.

The good news is that the ice threat is not as extensive as I had worried.  It appears that the transition from snow to ice to rain is rather quick so ice accumulation will be limited.

The coastal low is showing signs of forming over the Chesapeake Bay this morning and will continue to press north through the New Jersey coast this morning.  The low will further enhance the rainfall over the Philadelphia and New York City metropolitan areas through the morning hours.  A strong cold front will follow this afternoon with the heavy rain ending from southwest to northeast.  From there, the free fall begins, but more on that in the next post!

Here are some official snow totals from this storm so far:

NEW JERSEY

…MORRIS COUNTY…

BUTLER                 4.3   450 AM  12/9   SLEETING

DENVILLE               2.0   200 AM  12/9

…SUSSEX COUNTY…

WANTAGE                4.5   250 AM  12/9

HAMBURG                4.0   345 AM  12/9   HARDYSTON TOWNSHIP

…WARREN COUNTY…

BLAIRSTOWN             4.0   420 AM  12/9

HOPE                   2.4   505 AM  12/9   SLEETING

…BERGEN COUNTY…

RIDGEWOOD              2.0   400 AM  12/9   SKYWARN SPOTTER

…PASSAIC COUNTY…

WEST MILFORD           6.5   600 AM  12/9   PUBLIC

PENNSYLVANIA

…CARBON COUNTY…

LAKE HARMONY           5.0   240 AM  12/9

…LEHIGH COUNTY…

ALLENTOWN              2.9   450 AM  12/9   RAINING

…MONROE COUNTY…

TOBYHANNA              6.0   420 AM  12/9

…NORTHAMPTON COUNTY…

GLENDON                5.7   500 AM  12/9   SLEETING

TATAMY                 1.5   435 AM  12/9   MIXING W/ SLEET/RAIN

NEW YORK

…ORANGE COUNTY…

HARRIMAN               6.2   500 AM  12/9   PUBLIC

NEWBURGH               6.0   545 AM  12/9   SKYWARN SPOTTER

WASHINGTONVILLE        5.0   600 AM  12/9   PUBLIC

TUXEDO                 4.0   530 AM  12/9   PUBLIC

MIDDLETOWN             3.5   245 AM  12/9   PUBLIC

…SUFFOLK COUNTY…

STONY BROOK            1.2   350 AM  12/9   NWS EMPLOYEE

…WESTCHESTER COUNTY…

ARMONK                 3.0   430 AM  12/9   PUBLIC

CONNECTICUT

…FAIRFIELD COUNTY…

SHELTON                5.3   615 AM  12/9   PUBLIC

NEW CANAAN             3.8   425 AM  12/9   SKYWARN SPOTTER

BRIDGEPORT             2.0   515 AM  12/9   NWS COOP

…NEW HAVEN COUNTY…

SOUTHBURY              4.0   540 AM  12/9   SKYWARN SPOTTER

…NEW LONDON COUNTY…

LISBON                 2.2   543 AM  12/9   SKYWARN SPOTTER

9:35 PM

I have a feeling that I am going to be a very busy meteorologist through the New Year.  The active, cold pattern is well on the way of forming and organizing and the agreement on the GFS and ECMWF in the medium and long range guidance of the overall pattern structure is nearly uncanny.  Of course, if one has been keeping an eye on the stratosphere, MJO, and other atmospheric teleconnections, none of this would be a surprise.

My thoughts on the situation for Tuesday night into Wednesday have not changed much this morning.  The focus on Tuesday night and early Wednesday morning is northeastern Pennsylvania, northwestern New Jersey, the Hudson Valley, and interior Connecticut.  It is these locations where I believe the cold air will hold on the longest and the threat is the highest for significant ice accumulation.

Again, my suspicion is that the moisture advection combined with the strong isentropic lifting will lead to precipitation breaking out faster than currently expected on the model guidance.  This precipitation will not be heavy, but when it comes to sleet and freezing rain, only a few tenths of an inch are need to cause serious problems.  Precipitation will start as snow over a majority of the northern Mid Atlantic, but will quickly change over to sleet and freezing rain over the interior locations and rain along the coast and northern portions of the Philadelphia metropolitan area.  Sleet and freezing rain will continue over interior locations through early Wednesday morning, however by mid morning all locations will change over to rain.

Through the day on Wednesday, very heavy rain will fall throughout the region.  The cold front will move through in the afternoon with temperatures crashing through the 50′s and into the 40′s and 30′s on Wednesday night.  A much colder environment will be in place by Thursday morning.

The surface conditions on Thursday and Friday will be the coldest experienced thus far this winter season with temperatures in the mid to upper 20′s over the interior and upper 20′s to lower 30′s over much of the coastal plain for highs.  There is a growing agreement in the model guidance of a potential storm impacting much of the northern Mid Atlantic, with a focus along the coast, on Saturday afternoon through Sunday morning.  There also is a strong suggestion that warming will occur along the coast to change the snow over to rain.  This occurs due to the high pressure system sliding off the coast and producing a southwesterly flow ahead of the Sub Tropical Disturbance.  As a result, the boundary layer warms and precipitation changes over to rain.

However, there is a feature that will need to be watched in the next few days.  That feature is an Arctic cold front associated with the Polar Vortex over central Ontario.  The timing of these two features currently suggest that the coastal low moves north first and then interacts with the Arctic Cold front well off the New England coast.  However, a shift of a few miles in the guidance would lead to more interaction with the Arctic cold front and thus lead to a new infusion of fresh cold arctic air just as the coastal low starts to organize.  The introduction of such an air mass would also lead to rapid intensification of the low pressure system.  This potential is real and will need to be monitored as timing in this pattern will be key.

After the weekend storm, the negative NAO locks in as a positive PNA and negative AO pattern becomes established.  The pattern for the second half of December strongly suggest temperatures will average below normal.  However, even more interesting is the potential of the Sub Tropical jet stream to intensify in this time period, leading to several snow threats and a major snow threat around the official start of winter.  In short, buckle up this winter is just getting started!