FINAL CALL 7:00PM EST 12/13 (Mid-Atlantic/Northeast):

[RNS]

Update to forecast amounts for the Mid-Atlantic and northeast…and new totals for New England listed at the end of the post. First of all…some other problems related to this system.

As the surface low moves northeast parallel to the coast…strong winds will develop as pressures fall in response to the tightening pressure gradient…which will be aided by the departing high. With the strong easterly flow…moderate to significant coastal flooding and beach erosion are possible especially from new jersey northward…areas of southern/eastern new England coast and long island my be especially hard hit.

The departing high…Warm Ocean…and track of the low its self (with a very strong easterly and southeast wind component) will cause precipitation to change to sleet then rain during the height of the event across coastal areas of the Mid Atlantic and northeast. With total QPF of between 1.50 and 2.50”…combined with the recent snow melt and previous heavy rain event…the ground in some places will likely be unreceptive to such heavy rainfall.

12hr Flash Flood Guidance:

http://www.erh.noaa.gov/er/marfc/Maps/f ... oo12hr.gif

The Delmarva and coastal New Jersey may escape the worst potential for flooding…however areas further east especially just to the southeast of the Philadelphia metro area where 12hr FFG values are between 2.00 and 3.00” could be susceptible to some minor problems on northward into the New York City area and southeast New England. Further inland…where FFG values are lower…precipitation should remain of the frozen variety so the potential for flooding is diminished.

This afternoon/s 12z model initials were better than last nights 0z initializations however were not without problems. The ETA initialized 5MB too weak with regard to the low in the Gulf and the GFS initialized it 3MB too weak…both also had issues initializing the SFC pres field across the inter-mountain west and Rockies at the surface. At H5 the GFS initialized much better than the ETA and is too weak with the trough in the MS valley. The GFS had no significant problems making an assessment of the height field across this region. Both ETA and GFS did alright at H25 with the exception of problems with the OBS at RNK and SDM.

Overall I prefer the GFS over the ETA though at least 48 hours. ETA simply seems too warm in the mid levels.

There are some echo/s are beginning to show up already south of the PA/MD border…as initial area of WAA (associated with F vector convergence) though given the very dry air in place…not much (if any) of this is going to make it to the ground.

STJ s/w over the Midwest currently will continue to lift NE as a PJ s/w digs in behind the system…phases with the STJ s/w and allows the trough to tilt neg.
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_000l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_006l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_012l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_018l.gif

The h5 trough then makes an attempt (per the GFS 18z run) to close off at 42 hrs across the northeast.

http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_042l.gif

Surface low pres which is currently developing along the gulf coast will track eastward overnight and begin to transfer energy to a new low which will begin to take shape within the inverted trough along the North Carolina coast and track northeastward as it rapidly deepens. Making it close to the benchmark between 06z and 12z 12/15.

http://www.nco.ncep.noaa.gov/pmb/nwprod ... 6_006l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 6_012l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 6_018l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 6_024l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 6_030l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 6_036l.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod ... 6_042l.gif

GFS indicates the presence of a coupled jet pattern which would place much of the region in an area favorable for strong upward motions and increased precipitation rates.

As low pressure strengthens…tightening thermal gradient will ensue allowing frontogenesis to strengthen…thus prolonging the potential for CSI induced banded snowfall…even as shear increases and inertial instability starts to mix out. Generally snowfall rates will vary from 1-2”/hr with the potential for as much as 2-3”/hr underneath strong bands.

Areas in which the vertical column remains close to freezing throughout a deep layer in the mid levels (mainly below H7) will be the most susceptible to dynamic cooling…this will be especially important across Northeast PA/far NW NJ… the lower and mid Hudson Valley…W/C Mass (the Berkshires). Western CT (special emphasis on the Litchfield hills) into coastal sections of NH and Southeast ME. This may mean the difference between Heavy IP/FRZRA or +SN and could be the bust zone when it comes to accumulations if NO mixing takes place.

GFS 60-hr (event total) QPF ending 0z 12/16:

http://www.nco.ncep.noaa.gov/pmb/nwprod ... 0_060l.gif

Updated accumulation totals:

Major Cities:

Washington DC: 1-4” Snow to Rain.
Baltimore MD: 2-5” Snow to rain.
Philadelphia: 2-6” Snow/mix/rain.
New York City NY: 2-6” Snow/mix/rain.
Boston MA: 3-7” Snow/mix/rain.

Inland locations:

Roanoke VA: 2-4” Snow to Mix (Heavy icing likely)
Cumberland MD: 4-8” Snow/some mixing.
Martinsburg WV: 4-6” Snow/mix
Harrisburg PA: 6-10” Snow/mix
Allentown PA: 8-14” Snow/mix
Scranton PA: 10-17” Mainly Snow
Mount Pocono PA: 12-18” Mainly Snow
Montrose PA: 12-20” Mainly Snow
Binghamton NY: 14-22” Mainly Snow
Albany NY: 14-21” Mainly Snow
Pittsfield MA: 14-21” Mainly Snow
Torrington CT: 10-16” Snow/mix
Hartford CT: 8-12” Snow/mix (brief change to rain possible as well)
Fitchburg MA 9-14” Snow/mix. (Brief change to rain possible as well)
Providence RI: 3-5” Snow/mix/rain.

Totals for far northern New England will be out tomorrow.

[R0bb0871]

Great analysis RNS. Any thoughts on Dover, NJ? We are in Morris County, which is northwest New Jersey. Below Sussex Couny.

[RNS]

thanks...6-10" then a change to FRZRA

[Anonymous]

Par excellence, as usual!!!



-Jeb

[Guest]

Very reasonable RNS. Good job.

Any last minute thoughts out this way as my first flakes have just begun.......

[RNS]

2-5" king

[Anonymous]

RNS I think Woodbridge will see 1-3 tonight, but I heard a local forecaster say we would get 6 inches tonight.

Is that possible?

Thanks.


-Jeb

[Guest]

Wow you re going below the nws and my thinking.

Mind telling me why your thinking that low for here?

Im basing what i say by the models & radar trends/Sats and as well the "Fluff factor" which is and should be running at 15 to 20 - 1 ratio here.

[ChescoPASnowman]

Thanks!!!

Paul C

[RNS]

Wow you re going below the nws and my thinking.

Mind telling me why your thinking that low for here?

Im basing what i say by the models & radar trends/Sats and as well the "Fluff factor" which is and should be running at 15 to 20 - 1 ratio here.

I/m not convinced the precip lasts as long as what the WFOCLE indicates.

[RNS]

RNS I think Woodbridge will see 1-3 tonight, but I heard a local forecaster say we would get 6 inches tonight.

Is that possible?

Thanks.


-Jeb

I doubt woodbridge will see 6". 1-4" and then QUICKLY over to rain.

[donsutherland1]

Great detail and excellent synopsis, RNS.

Enjoy the snow in your part of PA.

[Stormchaser16]

RNS, what do you think for Hunterdon county? To see if my thinking is correct i expect to see 4-7" then iec/sleet/freezing rain and then eventually plain rain. Correct?

[rick-g]

RNS,
You are in line with nws and local Tv mets. (at least for this area). I suspect that I will be near the higher totals if no sleet or fr mixes in.

If I had my choice, I'll take the snow, I know what a bunch of ice will do.

[RNS]

first off rick...i/m doubtful that you will see any mixing w/ sleet let alone a changeover. soundings at AVP keep the column below freezing throughout the entire event.

and BTW thanks for the kind words from everyone.

[2001kx]

hey RNS i was wondering if you think there is any truth to this...its from a column by larry c.

"Excessive snowfall production: away from the coastline (just to the left of the track of the 850MB low), extremely high vertical velocities will interact with an unusually deep moisture fetch and orography to produce some staggering snowfall totals. There may be some brief "pollution" or reduction from sleet and freezing rain (per intrusion of a small warm layer near the core of the low). But communities along and 75 miles either side of an Elkins WV....Altoona PA....Rome NY....Rutland VT....Berlin NH....Houlton ME....Moncton N Br line may see anywhere from 18 to 48 inches of snow!"

[RNS]

Like i said in my post...the biggest problems will be where the vertical column is right at or just slightly below freezing (-0.0 to +0.5C)...this is where the very strong UVM has the potential to cool the column and keep precipitation as snow in the heavier bursts.

[Guest]

much better -- I am glad you lowered the snow amounts in I-95 cities they are still way too high IMO for NYC and philly

[JCT777]

RNS - good update on the snow amounts. They are still a bit higher than my current thinking, but of course I hope you verify.