December 7-8 Rain/Snow over Northeast...

By: Zachary Labe , 2:13 PM GMT on December 06, 2011

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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...
Radar...

Warnings...
Warnings...

NAO...
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)

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127. MariettaMoon
11:21 PM GMT on December 07, 2011
I don't expect the changeover to come in till about 10pm southeast of Blue Mountain.
Member Since: June 11, 2011 Posts: 36 Comments: 677
126. shipweather
11:18 PM GMT on December 07, 2011
this is taking too long
Member Since: December 15, 2007 Posts: 19 Comments: 987
125. TheRasberryPatch
11:17 PM GMT on December 07, 2011
42F with 1.02" of rain for the storm

Campbelltown, PA just east of Hershey

Are we tired of all this rain, YET
Member Since: January 26, 2007 Posts: 72 Comments: 6259
124. Zachary Labe
11:03 PM GMT on December 07, 2011
My weather station back home near Linglestown was 41F around 5pm.
Member Since: December 14, 2007 Posts: 284 Comments: 15112
123. MariettaMoon
11:01 PM GMT on December 07, 2011
I'm 44F at 6pm, about a 3F drop in the last hour.
Member Since: June 11, 2011 Posts: 36 Comments: 677
122. Zachary Labe
10:49 PM GMT on December 07, 2011
Quoting Hoynieva:


Same things happening to mine at present. It occurs from time to time for some reason. Nothing to do with my settings.

At the top of the comments sections click on the filter button and hit show all. Maybe that will help as I am not having problems on my end.
Member Since: December 14, 2007 Posts: 284 Comments: 15112
121. Hoynieva
10:42 PM GMT on December 07, 2011
Quoting PalmyraPunishment:
Also, a quick format question...

Why are TRP and MsriettaMoon's messages being hidden from me when nobody else's is? This is a new development...


Same things happening to mine at present. It occurs from time to time for some reason. Nothing to do with my settings.
Member Since: January 20, 2009 Posts: 0 Comments: 1503
120. Zachary Labe
10:37 PM GMT on December 07, 2011
Some light snow now here in Ithaca after a very wet and cold day. I guess it will be a night of curling up at the library studying as snow gently falls outside the window (more like being distracted by the blog and snow back home, lol).
Member Since: December 14, 2007 Posts: 284 Comments: 15112
119. PhillySnow
10:30 PM GMT on December 07, 2011
Quoting pittsburghnurse:
Snow and office Christmas party today. Now all that's left is to crack open that bottle of cabernet I won in the grab bag and sit in front of the fire.
Sounds great! I'm glad it's a little storm and you don't have to worry about being called back in to work. Enjoy!
Member Since: December 18, 2009 Posts: 0 Comments: 1235
118. wunderstorm87
10:27 PM GMT on December 07, 2011
41F here in northern Dauphin county with moderate rain. I've received 0.80" so far today.

It's tough to see since the winter weather advisories are overlayed over it, but there is a flood advisory for that band you mentioned in post 101 blizz.

19z HRRR Acc. Snowfall Map
Member Since: August 5, 2010 Posts: 0 Comments: 588
117. PhillySnow
10:27 PM GMT on December 07, 2011
All snow has been removed from our NWS forecast. Very sad. I'll just have to enjoy this storm vicarously - it's good to see excitement on the blog and I'm looking forward to some great photos! (hint.....)

.69 inches so far, temp is 51F; dewpoint 47. It's quite wet and balmy here. *sigh*
Member Since: December 18, 2009 Posts: 0 Comments: 1235
116. pittsburghnurse
10:26 PM GMT on December 07, 2011
Snow and office Christmas party today. Now all that's left is to crack open that bottle of cabernetI won in the grab bag and sit in front of the fire.
Member Since: October 14, 2006 Posts: 1 Comments: 639
113. PalmyraPunishment
10:21 PM GMT on December 07, 2011
Also, a quick format question...

Why are TRP and MsriettaMoon's messages being hidden from me when nobody else's is? This is a new development...
Member Since: January 31, 2007 Posts: 9 Comments: 2250
112. HeavySnow
10:20 PM GMT on December 07, 2011
Although Doug Hill on ABC 7 has just given me a little more hope.
Member Since: July 7, 2004 Posts: 18 Comments: 2989
111. HeavySnow
10:18 PM GMT on December 07, 2011
Quoting PalmyraPunishment:
What's this guy's deal? ^^ Quickly on his way to being ignored. Nobody likes a jackoff, pal.


I agree.

False info on the ability to snow above 32 degrees presented in a rude fashion.

Bring the punishment!

It's not looking good for me bwi. Maybe enough for a slushy snowball or ten. :D
Member Since: July 7, 2004 Posts: 18 Comments: 2989
110. PalmyraPunishment
10:14 PM GMT on December 07, 2011
near Harrisburg/Mechanicsburg
Member Since: January 31, 2007 Posts: 9 Comments: 2250
108. PalmyraPunishment
10:11 PM GMT on December 07, 2011
42 in Camp Hill...
Member Since: January 31, 2007 Posts: 9 Comments: 2250
107. MariettaMoon
10:02 PM GMT on December 07, 2011
I'm still at 47F at 5:00 pm

At 5pm, all snow line is about 55 miles west of Harrisburg at about 1500Ft.
Member Since: June 11, 2011 Posts: 36 Comments: 677
106. TheRasberryPatch
9:58 PM GMT on December 07, 2011
As for black ice - hmmm. Will the temps get below freezing? I know the snow will make the surface colder, but will it create black ice if the air temp is above 32F? Maybe Blizz could answer that.
Member Since: January 26, 2007 Posts: 72 Comments: 6259
105. TheRasberryPatch
9:56 PM GMT on December 07, 2011
I've been to Seven Springs once in the 80's and that is a really good resort for skiing for the Mid-Atlantic.

Temp is 44F with 0.90" of rain for the storm

Campbelltown, PA just east of Hershey
Member Since: January 26, 2007 Posts: 72 Comments: 6259
104. anduril
9:38 PM GMT on December 07, 2011
Quoting Blizzard92:
Seven Springs Ski Resort
Impressive! My boss is letting me take off tomorrow so I'm hoping I'll have a bit of snow to play in. At least I'll get to stay up to watch the whole thing develop and maybe we'll even get some thundersnow out of it :)
Member Since: August 29, 2006 Posts: 0 Comments: 170
103. Zachary Labe
9:37 PM GMT on December 07, 2011
Seven Springs Ski Resort
Member Since: December 14, 2007 Posts: 284 Comments: 15112
102. anduril
9:35 PM GMT on December 07, 2011
Just dropped below 43f (42.6f) in Mechanicsburg while New Cumberland is sitting at 44f which is still a nice drop from 11:30am when weather.com was saying we were at 51f. Couple more degrees to go and we should be rocking
Member Since: August 29, 2006 Posts: 0 Comments: 170
101. Zachary Labe
9:33 PM GMT on December 07, 2011
Look at that bright banding in Juniata County, wow! Probably some massive snowflakes!
Member Since: December 14, 2007 Posts: 284 Comments: 15112
All snow now, finally, and coming down pretty good.
Member Since: Posts: Comments:
Quoting anduril:
Actually, it doesn't have to be 32f for snow. It just has to be at or below freezing in the UPPER atmosphere for snow to generate. As we saw in the October storm it was above freezing through most (if not all) of the event in central pa but snow still fell, and accumulated quite nicely

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!
Member Since: December 14, 2007 Posts: 284 Comments: 15112
Quoting frankfish:

It needs to be approximately 32 degrees above zero in order to snow, my friend.
Actually, it doesn't have to be 32f for snow. It just has to be at or below freezing in the UPPER atmosphere for snow to generate. As we saw in the October storm it was above freezing through most (if not all) of the event in central pa but snow still fell, and accumulated quite nicely
Member Since: August 29, 2006 Posts: 0 Comments: 170
A bit earlier than I expected for the changeover in State College. Looking at tower cams, it appears like very heavy snow is falling in the Laurel Highlands with roads covered. There could be some 12in totals around there before this is all said and done.

Back to a pathetic rain here at Cornell... just unbelievable, lol
Member Since: December 14, 2007 Posts: 284 Comments: 15112
State College is reporting some mixing.
Member Since: December 14, 2007 Posts: 284 Comments: 15112
Something to think about with all the rain and snow and cooling temps:

...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.
Member Since: Posts: Comments:
What's this guy's deal? ^^ Quickly on his way to being ignored. Nobody likes a jackoff, pal.
Member Since: January 31, 2007 Posts: 9 Comments: 2250
From CTP:

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
Member Since: January 31, 2007 Posts: 9 Comments: 2250
Quoting weatherman321:
Light Snow now being reported at Pittsburgh international airport. temp - 34


Snow has now began here in Greensburg, PA - About an hour before it was suppose to change over
Member Since: Posts: Comments:
down to 45f here in camp hill...
Member Since: January 31, 2007 Posts: 9 Comments: 2250
Light Snow now being reported at Pittsburgh international airport. temp - 34
Member Since: Posts: Comments:
83. bwi
LWX pushed the snow accumulation line west again.

And now, a flood warning for the DC area. Great.
Member Since: Posts: Comments:
Wet snowflakes finally mixing in up here.
Member Since: December 14, 2007 Posts: 284 Comments: 15112
Snowflakes are just now beginning to mix in with the rain in Altoona.
Member Since: Posts: Comments:
Quoting Sockets:
Looking like its going to be mainly rain here in Kittery, but it stayed much cooler than expected today...hoping we get lucky and get a change over to snow sometime earlier tonight.


I think I'm gonna start chucking ice from my freezer outside to help speed up the cooling process....heh
Member Since: Posts: Comments:
Looking like its going to be mainly rain here in Kittery, but it stayed much cooler than expected today...hoping we get lucky and get a change over to snow sometime earlier tonight.
Member Since: Posts: Comments:
40N, 74W
Flood watch till 2359 hrs
Rain = 0.70 +
BM = 1005 mb F
Winds SW 2 G4
Member Since: Posts: Comments:
Hey Blizz its about 37 degrees currently in Greensburg, PA .. change over not expected till 4 ... but Laurel Highlands seeing snow and areas to the east are seeing a mix precip. do you think change over could occur sooner than expected?
Member Since: Posts: Comments:

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About Blizzard92

Cornell University- Atmospheric Sciences Undergrad; Research Assist.- Onset of Spring Indices Toolbox; Interests- Small spatial scale climatolology

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Linglestown, PA
Elevation: 520 ft
Temperature: 24.2 °F
Dew Point: 15.2 °F
Humidity: 68%
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Updated: 10:37 AM EST on January 18, 2014

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