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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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?
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Quoting PalmyraPunishment:
48 degrees in Camp Hill.

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.
Member Since: December 14, 2007 Posts: 285 Comments: 15140
48 degrees in Camp Hill.

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.
Member Since: January 31, 2007 Posts: 9 Comments: 2250
Heavy snow falling in the Laurel Highlands already!
Member Since: December 14, 2007 Posts: 285 Comments: 15140
so far most of the heavy rain is to our west, thankfully. Still @ 50F
Member Since: January 26, 2007 Posts: 72 Comments: 6276
Still 50f here in Camp Hill. Temps just are not crashing yet.
Member Since: January 31, 2007 Posts: 9 Comments: 2250
70. bwi
NWS is moving the accumulation line back east, at least compared with when I checked yesterday.
WWA's for the northern and western DC suburbs. That's pretty cool. I hope HeavySnow gets enough to make snowballs!
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KBGM was reporting unknown precip. at the 8:00am report at 35F.
Member Since: December 14, 2007 Posts: 285 Comments: 15140
68. bwi
Minor flooding in DC area. The trail I ride to work on was flooded slightly (8") near the river. When this gage gets above 4 1/2 ft, the trail floods. Funding for river gages has been cut, so if you rely on them like I do, always good to remind your gov't reps that they're useful for more than fishermen and environmental researchers!
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Quoting Mason803:



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.
Member Since: January 26, 2007 Posts: 72 Comments: 6276
Quoting TheRasberryPatch:
Oh one other thing...I was talking to a contractor and he mentioned with all the rain we have receieved this Fall and year, the grounds are so saturated even on a few days of dry weather the ground is squishy. He said if the ground is like that when it finally gets cold and the ground freezes we may see more trouble. The ground may freeze down a couple of feet, where pipes are located. Not just the usual 6" or so.
Something else to be worried about this Winter.



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.
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Quoting TheRasberryPatch:
Oh one other thing...I was talking to a contractor and he mentioned with all the rain we have receieved this Fall and year, the grounds are so saturated even on a few days of dry weather the ground is squishy. He said if the ground is like that when it finally gets cold and the ground freezes we may see more trouble. The ground may freeze down a couple of feet, where pipes are located. Not just the usual 6" or so.
Something else to be worried about this Winter.
Thanks for alerting us, TRP.
Member Since: December 18, 2009 Posts: 0 Comments: 1273

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.
Member Since: February 27, 2009 Posts: 0 Comments: 2949
Oh one other thing...I was talking to a contractor and he mentioned with all the rain we have receieved this Fall and year, the grounds are so saturated even on a few days of dry weather the ground is squishy. He said if the ground is like that when it finally gets cold and the ground freezes we may see more trouble. The ground may freeze down a couple of feet, where pipes are located. Not just the usual 6" or so.
Something else to be worried about this Winter.
Member Since: January 26, 2007 Posts: 72 Comments: 6276
12z NAM is a hair colder and brings snow up here towards Ithaca. We shall see up here I guess. Given the dynamics of the system, I think there will be a few surprise heavy accumulations somewhere in central Pennsylvania.
Member Since: December 14, 2007 Posts: 285 Comments: 15140
Quoting Blizzard92:

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.
Member Since: January 26, 2007 Posts: 72 Comments: 6276
lwx advisory update saying heaviest snow between 8pm to midnight with 2-4" accum along with wind gust to 40mph. (hagerstown/frederick areas)
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Quoting TheRasberryPatch:
It appears that the snow event won't be a significant amount of snow. I think the highest amount I see is 6".

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.
Member Since: December 14, 2007 Posts: 285 Comments: 15140
It appears that the snow event won't be a significant amount of snow. I think the highest amount I see is 6".

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
Member Since: January 26, 2007 Posts: 72 Comments: 6276
We're still under a flood watch here. Chance of snow from 3am - 4am, according to NWS. lol If this holds true, I'll be up.

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!
Member Since: December 18, 2009 Posts: 0 Comments: 1273
I made a few very minor adjustments in my selected city accumulation list and to the snow map. See above...
Member Since: December 14, 2007 Posts: 285 Comments: 15140
WOW!! here in Westmorland County, PA we went from just cloudy last night to today NWS saying Rain/Snow 100% today 1-2inches and tonight Snow likely with 1-3inches... and winter advisories/warnings are now up. that is just crazy.
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Quoting anduril:
Seeing wildly varying amounts of snow and time that the changeover starts this morning on the news. Amounts seem to be swinging anywhere from 1-6in and start time seems to vary even more wildly from late afternoon to 7, 9, and 11pm.

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.
Member Since: December 14, 2007 Posts: 285 Comments: 15140
Seeing wildly varying amounts of snow and time that the changeover starts this morning on the news. Amounts seem to be swinging anywhere from 1-6in and start time seems to vary even more wildly from late afternoon to 7, 9, and 11pm.

Any thoughts blizz?
Member Since: August 29, 2006 Posts: 0 Comments: 173
Yucky rain and 57 here in Annandale, VA
Member Since: July 7, 2004 Posts: 18 Comments: 2990
Good morning! I went to bed really early last night! Just was a bit a tired and stressed from studying! Anyways last night's runs have been a bit less amplified allowing the precipitation shield to spread a bit more northwest. I may even be able to see some snow, woohoo! Snow map looking pretty good except could be expanded northwest. I will be here most of the morning on the blog then...
Member Since: December 14, 2007 Posts: 285 Comments: 15140
Looks like we could get something decent up here! Last thing we need is another storm the week before finals. The end of the semester can't come soon enough!

How are you faring blizz? I know i'm becoming more tired week by week and becoming less focused (not good).
Member Since: February 23, 2010 Posts: 0 Comments: 685
Beautiful Sunset I took video of Link
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I suspected the low would be further west than the models were showing a couple days ago and having the low just east of the apps. The snow axis looks like it will shape up along the south apps NNE into New England. This a great scenario for the inland areas but bad for the I-95 Corridor which will mainly rain with perhaps trace amounts from backend snow.

GFS 00z Snow map:

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Jeeze, talking about 2.50" rain from DC to NYC.
Member Since: June 11, 2011 Posts: 36 Comments: 677
Quoting PalmyraPunishment:
From Steven DiMartino, NYNJPAWeather.com for the Harrisburg area

Snow fall amounts of 4" to 8" with local amounts up to 12" above 1,000 feet in elevation.


Boy, that's rollin on the high side...
Member Since: June 11, 2011 Posts: 36 Comments: 677
Wow. Potential for snow within 24 hours and almost silent on the blog. Unheard of! Do I hear crickets??
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From Steven DiMartino, NYNJPAWeather.com for the Harrisburg area

Snow fall amounts of 4" to 8" with local amounts up to 12" above 1,000 feet in elevation.
Member Since: January 31, 2007 Posts: 9 Comments: 2250
42. bwi
Flood watch for DC. Great.
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Quoting wunderstorm87:
Light snow is being reported in Shreveport, LA right now (Link). This is associated with the beginning of the low that will come up the coast.




Not out my window!
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Light snow is being reported in Shreveport, LA right now (Link). This is associated with the beginning of the low that will come up the coast.
Member Since: August 5, 2010 Posts: 0 Comments: 588
Member Since: January 31, 2007 Posts: 9 Comments: 2250
Thanks, Blizz.

Imagine me being too far north to get any real snow.
That seems crazy, but sometimes the Universe holds the weather map upsidedown.
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NAM coming in pretty warm, I hear.
Member Since: January 31, 2007 Posts: 9 Comments: 2250
Flooding could be a problem before the snow given the large amount of rain that will fall Wednesday afternoon (~1.5"), especially in Lancaster & Lebanon counties. Some of those areas saw 0.5-1" today.
Member Since: August 5, 2010 Posts: 0 Comments: 588
Hey, I'll be happy with an inch to boost the spirit. Anything more I'll consider a bonus. State College has Marietta at 2.2" from 7pm Wed to 3am Thu.
Member Since: June 11, 2011 Posts: 36 Comments: 677
Hey Blizz - Any thoughts on what the western Catskills might get out of this storm ? I'm trying to start a ski instructor gig at a mountain out there but they haven't even been able to make snow nevermind get any of the "real" stuff...

This might be the break they've been looking for...

Thanks !
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Quoting Blizzard92:
Latest model guidance is edging this precipitation shield as far west as Pittsburgh.


Really? what does it look like? and what model guidance? Last night it look like we would be lucky to see some clouds lol.
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WU forecast finally has snow mentioned in the forecast. I guess they get the information from NWS. Blizz has mentioned this for over a day and NWS is just mentioning snow.

Been stuck on 59F most of the day. 0.25" of rain so far
Member Since: January 26, 2007 Posts: 72 Comments: 6276
Quoting wxgeek723:
On another note, they named this one 'Ayrshire'. Not quite following the theme this year...British locations?


Hahaha... I didn't catch that. Thanks for posting. hmmm I have no clue what the theme is.
Member Since: December 14, 2007 Posts: 285 Comments: 15140
On another note, they named this one 'Ayrshire'. Not quite following the theme this year...British locations?

Member Since: August 28, 2008 Posts: 79 Comments: 3714
Harrisburg PA has passed 70" for precipitation so far this year. 70.64". No annual total in the 60s before. Going for 6 feet with this storm?
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Latest model guidance is edging this precipitation shield as far west as Pittsburgh.
Member Since: December 14, 2007 Posts: 285 Comments: 15140
Quoting bwi:
2-day precip -- lots of water, which we don't need.
We've got a flood watch tomorrow. *sigh*
Member Since: December 18, 2009 Posts: 0 Comments: 1273

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

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