December 7-8 Rain/Snow over Northeast...
Current teleconnections and wavelengths continue to support a very mild pattern for much of the eastern CONUS over the next 2-4 weeks at the minimum. But there are still remain chances of snow in some areas given the right setup. A cold front will move through the region as a shortwave develops and moves along the front. Cold air advection will transition some areas from rain to heavy snow, but it will be a close battle for temperatures as a 1-2 degree difference will make this a very difficult forecast.
Thoughts on December 7-8 Rain/Snow Event
A strong cold front is slowly moving across the Northeast with several shortwaves moving up along the boundary. The first wave is moving through Tuesday night through Wednesday morning with a swath of moderate to heavy rain. As the front slowly moves east, cold air advection will filter cooler air into the region as temperatures fall into the mid to upper 30s by dusk. Rainfall amounts will range from 0.5in to 1in for most areas south of interstate 80. It will be a race for timing as precipitation begins to move back into the region by Wednesday evening and colder air begins to filter in from the northwest. The strength of the cold air remains weak with the lack of anticyclone to the north and absent blocking upstream. H85s will drop below 0C as far south as the Pennsylvania turnpike by Wednesday evening along with 1000-500mb thicknesses around 538dm.
A heavy axis of deformation precipitation will wrap around the second shortwave Wednesday night with several convective indices indicating high QPF rates. Impressive dynamics with weak cold air advection should transition the rain to snow from the northwest to the southeast Wednesday night across Maryland and Pennsylvania up to New Jersey. Heavy snow will fall at the rate of 1-3in/hr for a short 2-3 hour period. 2m temperatures will remain marginal and hover possibly above freezing for a duration of the event. Given warm and wet ground conditions and marginal temperatures, accumulations will be limited at first until snow rates become higher. Snow ratios will be limited to 10:1 for most areas, but higher ratios are likely during heavier rates with excellent dendritic growth zones being indicated on SKEW T charts. Most of the accumulation for the Middle Atlantic will occur during the overnight hours after rush hour and before the morning commute. This will limit impacts.
It is possible given current wavelengths that this low pressure continues to trend northwest. Given this potential my forecast for snow accumulations has been given a slight warmer bias. It is possible my accumulations may be too heavy given the marginal temperatures. But if rates are heavy enough there is the possibility for higher amounts with localized locations nearing a foot of snow. This will likely be limited to the higher elevations above 1000ft which have the best chance at winter storm warning criteria. This is a very difficult forecast and is very similar to the October event for snow axis placement. Marginal temperatures continue to play the biggest factor in the forecat. There will be no sleet or freezing rain in this event given the extent of the boundary layer warmth.
Most I-95 locations will stay primarily rain through the event. For areas towards New England a similar progression of rain to heavy snow is likely Wednesday morning into early afternoon and will be very similar to the Middle Atlantic. Most of the snow will be west of the coastal plain especially towards the higher elevations of western Massachusetts and northwestern Connecticut.
If the cold air advection filters in time, it is likely the Lower Susquehanna Valley along and above the turnpike through the southern Poconos will receive the highest accumulations with the possibility for 4-9in of snow. But for now I will forecast lower amounts. See below.
Radar...
Warnings...
NAO...
This is my current rain/snow line...
Winchester, VA - Frederick, MD - Westminster, MD - Coatesville, PA - Pottstown, PA - Quakertown, PA - Hillsborough, NJ - Peekskill, NY - Hartford, CT - Worcester, MA - Manchester, NH - Augusta, ME - Bucksport, ME
*Along and to the north and west of this line will be the highest snow accumulations and predominately remain snow throughout the event. South of the line will feature a mix or plain rain with limited to no snow accumulation. Elevations above 1000ft along and northwest of this line will feature the highest snow totals.
Storm Reports...
None.
Storm Impacts...
1. Quick moving storm with impacts less than 12 hours during early morning hours with low societal impact.
2. Brief periods of heavy snow of 1-2in/hr.
3. Wet snow with high water content as snow ratios remain around 10:1.
4. Higher elevations above 1000ft may see upwards of 7in or more.
5. Snow may fall at temperatures of only 32-34F for duration of event.
Snow Map...
*I put this map together rather quickly, but I wanted to show a generic distributation of the snowfall totals to help make my forecast a bit more simple to understand. The 3-6in range will have the highest snow totals with locally higher amounts possible (especially above 1000ft)
Selected City Accumulations for the Northeast...
Hagerstown, MD- 2-4in of wet snow
Baltimore, MD- Up to 1in of wet snow in some areas
Salisbury, MD- Heavy rain
Pittsburgh, PA- Light snow up to 1in
State College PA- Light snow. Accumulations 2-6in
Williamsport, PA- Light snow. Accumulations of 2-6in
Altoona, PA- Light to moderate snow. Accumulations 3-6in
Harrisburg, PA- Rain changing to heavy snow. Accumulations 2-5in
Lancaster, PA- Rain changing to snow. Accumulations 1-3in
Philadelphia, PA- Rain mixing with snow. Little to no accumulation
Allentown, PA- Raing changing to heavy snow. Accumulations 2-5in
Scranton, PA- Moderate snow. 2-5in of accumulation
Washington, DC- Rain mixing with a few flakes at end. No accumulation
Wilmington, DE- Primarily rain mixing with a few flakes at end
Dover, DE- Heavy rain
Trenton, NJ- Mostly rain changing to rain/snow. Little to no accumulation.
New York City, NY- Mostly rain changing to rain/snow. Little to no accumulation.
Poughkeepsie, NY- Moderate snow. 3-6in of accumulation
Binghamton, NY- Light snow. Accumulations 2-4in
Ithaca, NY- Light snow. Accumulations 1-2in
Albany, NY- Light snow to moderate snow. Accumulations 2-6in
Hartford, CT- Rain changing to snow. 1-3in of accumulation
Concord, NH- Light snow. 1-4in of snow is possible
Providence, RI- Heavy rain
Worcester, MA- Rain to moderate snow. 1-4in of accumulation
Boston, MA- Mostly rain changing to rain/snow. Up to 1in is possible in some areas
Nantucket, MA- Heavy rain
Hyannis, MA- Heavy rain
Portland, ME- Rain to rain/snow. 1-2in of wet snow is possible
Bangor, ME- Rain to heavy snow. 2-5in of snow is possible
"Subject to Change"
Model Analysis
Current guidance has been edging the position of the low pressure farther northwest while weakening the first shortwave and strengthening the primary low. This trend will likely continue slightly northwest with limited blocking upstream enhancing uncertainty for many forecasts at the cusp of the rain/snow line. Current SREF and GEFS ensemble means suggest widespread 1-1.5in QPF amounts well inland towards I-81 with a sharp cutoff to the northwest. Ensembles are continuing to shift northwest in QPF and likely will continue to do so by about 25-50 miles. The NAM remains on the colder edge of the envelope suggesting very high snow amounts for parts of east-central Pennsylvania up through northwest New Jersey and up through central New England. Given my analysis this morning, it appears the NAM is already running a bit too cold given 2m temperatures in the low to mid 50s for most observing sites. GFS remains the farthest southeast of guidance and given the nw shift in the ensembles, it likely remains too far southeast and can be disgarded.
ECMWF is a mean between the GFS and NAM operational models and therefore has the highest concentration. Model QPF remains similar with 1in amounts as far northwest of Harrisburg, PA. Much of this QPF is progged as snow, although I believe guidance is running a bit too warm for boundary layer temperatures and there I am cutting snowfall QPF totals in half accounting for factors such as wet and warm ground temperatures, poor snow ratios, and above freezing boundary layer temperatures.
After the Storm
The continued +AO and +NAO will dominate the long range with little to no blocking in the northern Atlantic. Current MJO phases support an instilled mild pattern over the eastern contiguous United States with limited chances of wintry weather through the end of the month. As my December forecast alerted to, it is likely another very mild spell is possible mid to late month perhaps towards the holidays as the EPO begins to retreat to a positive anomaly. In the shorter term colder (seasonable to slighty below normal) temperatures are likely under a west-northwest flow. Given the lake of cyclonic flow, lake effect snows will remain unorganized for the most part with a snow drought continuing across the Great Lakes. Any chances of lake effect snow will be limited to directly after frontal passages.
A weak clipper will move across upstate New York and northern New England with the threat of light snow. Moisture will be lacking, but orographic lift may aid in the possibility for a coating to two inches of snow in some areas Friday night. A brief period of lake effect snow is likely over the weekend under a northwest flow. Given the reduced north Atlantic blocking and the return of the unfavorable Alaskan vortex, most storm systems will have a higher likelihood of moving up through the Great Lakes. This will favor a snowy pattern towards the Midwest. Enjoy the the taste of winter this system provides as chances will remain minimal ahead.
Please post storm reports in this blog from across the Northeast during the winter storm and please post location of observation in each report...
This blog is in progress. Check back soon...
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Lower Susquehanna Valley Doppler...
(Courtesy of WGAL)
Reader Comments
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Any thoughts blizz?
Start time is the big question of the day. Until the cold front gets a bit closer, there is very little way of picking a time other than guessing. I am going to update my selected city accumulation list above in a hour or so. But I like my call for 2-5in for KMDT.
I'm looking forward at least to watching how the storm develops and seeing the reports from those who get some snow. Good luck to all!
This is one weird system...An 'Areal Flood Watch and Winter Weather Advisory' on the same day....Really? Around these parts we rarely get heavy rain changing to accumulating snow with temps this high. It might occur in Colorado or the Rockies, but not hardly here.
So far 0.57" of rain for the storm
The last time I can remember a flood watch with a winter weather advisory/warning was back around the St. Patrick's Day Storm of 2007 with heavy rain followed by 10in of snow. Also didn't the October storm this year have a flood watch too? I could be wrong.
It may have been. I meant to say these two storms are weird. Usually the cold air ushers in drier air and we may see some flakes, even a dusting, but that is all.
Something else to be worried about this Winter.
40N 74W
Flood watch to our west. 59 deg calm winds pressure 1013 mb rain. The late Oct storm had snow for 3 hrs w/ no accum. Only one forecast for up to 1 in as the storm bombs out off the coast. Think east of 95 to the GSP ice may be the big problem. Think our man in Ossining has a range of 0-2 from Upton , 3-6 by Blizz and 6-10 from the source showing 1 in on the North Jersey coast. Mt Holly calling for the low to bomb off the coast this afternoon to early evening.
Prediction no igloo amounts here.
that doesn't sound good for my irrigation at the golf course. We blow out all the lines in the fall but you can't get 100% of the water out.
It's just something to keep in the back of your mind.
WWA's for the northern and western DC suburbs. That's pretty cool. I hope HeavySnow gets enough to make snowballs!
What time do you think the changeover could occur, Blizz? Unfortunately, I have to do a bit of traveling this evening (9:00 PM) and I'm wondering if I should adjust that a bit.
I am not completely sure, but I would think 7-9pm is fair game for a changeover. The snow will last less than 6 hours but will come down at 1-2in/hr.
Flood watch till 2359 hrs
Rain = 0.70 +
BM = 1005 mb F
Winds SW 2 G4
I think I'm gonna start chucking ice from my freezer outside to help speed up the cooling process....heh
And now, a flood warning for the DC area. Great.
Snow has now began here in Greensburg, PA - About an hour before it was suppose to change over
HPC SNOW GUIDANCE HAS BACKED OFF ON THE SNOW AMOUNTS FOR CENTRAL
PA...BUT WILL HOLD ONTO WINTER WX ADV AND WARNINGS THAT ARE
ALREADY IN PLACE FOR NOW
...AREAS OF BLACK ICE TONIGHT...
THE NATIONAL WEATHER SERVICE IS CAUTIONING THAT AREAS OF BLACK ICE
CAN FORM TONIGHT, EVEN ON PAVEMENTS WITHOUT ANY SNOW ACCUMULATION.
AS TEMPERATURES DROP BELOW THE FREEZING MARK OF 32 DEGREES, WET
UNTREATED PAVEMENTS CAN BECOME ICY, REGARDLESS OF WHETHER ANY SNOW
HAS ACCUMULATED ON THESE SURFACES OR NOT. SO TAKE EXTRA CARE IN
YOUR TRAVELS TONIGHT.
Back to a pathetic rain here at Cornell... just unbelievable, lol
Yep, in fact most of the snow that will fall will be at temperatures of 32-34F for this storm. Up here in Ithaca it is a rain/snow mix at 36F. On some days, I have seen snow showers with temperatures as warm as the mid 40s!
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