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Western Pa / Pittsburgh area Winter Discussion ❄️☃️

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Winter Weather Advisory

National Weather Service Pittsburgh PA
843 PM EST Tue Dec 1 2020

Including the cities of Aliquippa, Beaver Falls, Ambridge,
Monaca, Pittsburgh Metro Area, Indiana, Washington, Canonsburg,
Waynesburg, Murrysville, Greensburg, New Kensington,
Lower Burrell, Latrobe, Monessen, Uniontown, Weirton, Follansbee,
Wellsburg, Wheeling, Moundsville, New Martinsville, Fairmont,
and Morgantown
843 PM EST Tue Dec 1 2020


* WHAT...Snow expected. Additional snowfall accumulations between
  1 to 2 inches.

* WHERE...Portions of western Pennsylvania and northern West

* WHEN...until 7 AM EST Wednesday.

* IMPACTS...Travel will remain difficult.


Slow down and use caution while traveling.

Please report snow or ice by calling 412-262-1988, posting to the
NWS Pittsburgh Facebook page, or using Twitter @NWSPittsburgh

The Pennsylvania Department of Transportation and Pennsylvania
Turnpike Commission remind motorists to adjust speeds based on
driving conditions as winter weather impacts Pennsylvania
roadways. Visit www.511pa.com for the latest travel, roadway and
traffic conditions.


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10 hours ago, KPITSnow said:

I feel like this is the type of storm track we haven’t seen in years....and when we have there hasn’t been enough cold air wrapping in.

The CMC quickly abandoned this look, waiting until the storm was off Maine's coast to wrap it up.

The Euro shows a prototypical Miller A path from the Gulf, through Alabama/Georgia, and then setting it up off the Delmarva.  The GFS has a very similar setup, a bit more convoluted, but there's no "snow side" or cold sector.  It's all rain and shears off south of our area.  Lack of cold air definitely is one concern.  Seems this one might be an inland NE special.

Really, I think 2010 was the last of this kind of storm.  Pittsburgh is still long overdue for an 8"+ event.

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Well, it's been quiet here.  Rightfully so, I guess, because there isn't much going on in the interim.  Long-term, the signals keep flipping back and forth, but a -NAO appears relatively likely.  Perhaps in 48 hours we're back to a NINA look, I don't know, but it has been quite a while since we've seen any kind of true, even transient, -NAO block during the winter months.  The last -NAO for December I can find is 2009 (we remember what happened then).  From a "winter" perspective, 2010 was it, with negative values quite literally the entire year and into 2011.

2009  -0.01   0.06   0.57  -0.20   1.68  -1.21  -2.15  -0.19   1.51  -1.03  -0.02  -1.93
2010  -1.11  -1.98  -0.88  -0.72  -1.49  -0.82  -0.42  -1.22  -0.79  -0.93  -1.62  -1.85
2011  -0.88   0.70   0.61   2.48  -0.06  -1.28  -1.51  -1.35   0.54   0.39   1.36   2.52

Columns after the year run from January to December.  That was the end of our blocking winters.  Since then, the only real blocking has come during the summer or fall months, and all winters have averaged well above positive.  "A decade under the influence."

This might all be for naught, but I figured since there isn't much going on, I'd try my hand at some analysis for the upcoming period, which looks like it could be surprisingly active.


First is the Canadian for next Tuesday.  After this weekend, which pretty much all models are visualizing a cutter, we head into next week that really looks more interesting.  We see it is holding a rather large, singular piece of energy back into the southwest.  This is usually a good sign for a big NE snowstorm.  There's ridging along the west coast and, although the flow looks transient ahead, I think this is more a symptom of this s/w digging.

This is the GFS at the same time:


The GFS is much less organized.  It is stringing out some of the same energy all over, while also holding a bigger piece back off the coast.  It comes crashing in a few frames later:


That's the remaining piece of energy coming into Seattle.  Still, it keeps it separate and moves some smaller bits out ahead into the great lakes area.  Very northern-stream dominant.  At the same time, the Canadian keeps bowling:


Now it's a closed-off ULL.  Pretty much concentrating all the energy right there near the four corners.


The Canadian then digs this all southward into the Gulf, dragging and phasing the northern stream energies into one significant trough.  On the GFS, however:


The American model keeps the streams separate.  It has these two distinctive blocs, but it also has a piece of NS energy holding up in Canada.  Basically, instead of how the Canadian crashes all this energy together into a cohesive system, the GFS times them apart and prevents things from ever morphing.  It's a strung-out mess.  See the final GFS look here:


As I just said, the GFS is strung-out and tries to dig some of the energy south, but the northern stream is still keeping other bits of energy off the same conveyer belt.  Eventually it does form a Miller A (of sorts) on its own, but because of the separation here, the cold air is also pulled away and the trailing system (seen here digging into TX) has no cold air to work with.  What we get is a rain storm.  Meanwhile, the Canadian:


Puts a nice closed-off bowling ball right over the Jersey shore.  Even the Canadian setup is kind of off-kilter - resulting in a double-barrel low of sorts - but it brings a lot of snow into the Mid-Atlantic.  It isn't a great look for Pittsburgh because of the confluence, but if shifted just a little to the northwest, Pittsburgh would be in the game for the bigger totals.  Meanwhile, this verbatim would jackpot areas around D.C., Philly, and New York, almost 11 years to the day after a very similar system did the same.

The remaining question is - which of these models has support?  As of the 12Z runs today, it looks like every model is kind of doing its own thing.  There isn't a ton of agreement on the evolution of these pieces of energy.  To be expected at this range and with this many moving pieces.  Clearly it will take some time to lock in the results, but at least for now, we do have a period to watch upcoming.

Whether anything results is pure speculation.  Given how this winter was expected to develop as a STRONG NINA (now backing off that idea considerably, to the point where the Nina may be collapsing imminently), I think this is about as positive as we could have hoped.

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18 hours ago, ChalkHillSnowNut said:

Great write up Jwilson!!

I’ll echo that sentiment. 

Looks like the upcoming blocking regime may help mute the Nina effects. It really just started showing up, a few days ago it looked like lights out for awhile. In my experience that’s usually how it goes when the blocking actually happens; models catch on in the medium range rather than chasing day 14 “trends”.

If we can get the pacific just little more favorable (more ridge out west) that would aid our chances. Either way it looks active next week, I’d be surprised if there isn’t at least one good snow storm somewhere in the East. Time will tell how many rolls of the dice we get. If blocking is a recurring theme that should help make this a decent year despite the Nina.

Now watch the incoming geomagnetic storm fudge up the stratosphere and wreck the blocking. :lol:

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51 minutes ago, ChalkHillSnowNut said:

Yea but the trend is our friend-it keeps pushing more energy back west due to negative tilt....we’ll see and hope-our Friends out in CPA are due tho! 

Stronger storm \ negative tilt trough sooner and or slightly less confluence to the north and I think it could easily shift enough to get us more involved. Of course things could trend the other way and we are partly cloudy cold and dry. Either way, we all know what was modeled today is very unlikely to be the exact end result hence why people always say they don't want to be in the bullseye 5-6 days out.

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There's still quite a few ensemble members of the GFS and Euro that swing a good bit of snow back across the entire state.  Ridging out west, the digging s/w, or the high pressure can all influence the direction the low(s) move.  The Canadian came right back to the same solution it had a couple days ago, however.  It will be interesting to see if it remains consistent.  It was curious to see the Euro come around to that same solution today while the GFS hints a bit more at it, but keeps the flow too progressive.  Maybe the GFS is the new Dr. No.

The GFS keeps it active through the period.  The Euro looks like it transitions to a real +EPO signal around Christmas (not good).  It will be curious to see what ends up winning out if the AO keeps tanking while we have less pacific ridging.  Perhaps we get an "artificial" -EPO due to a shifting or splicing of the PV.

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3 hours ago, jwilson said:

Case in point: the EPS has a 60-80% chance of Pittsburgh metro seeing more than 3" of snow this week and a 30-40% chance of 6" or more with a mean through Friday of 5".  Game isn't over.

Yeah, Nobody should be discounting any outcome, case in point just quickly looking at 18z GEFS there are more members getting the whole state in on the action.

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2 hours ago, CoraopolisWx said:

Not exactly the same setup, but this was an early holiday present. Early dismissal Thursday the 10th, and school closed on Friday. :snowing:


That was so close to being a epic storm. Double digit snows over most of the area, but just missed a widespread 2-3’

(of course that happened anyway 3 months later, and close to that again 13 months later. Good times)

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2 hours ago, north pgh said:

I’m liking the trends for the coming week. A little more west or a more robust system system so we can all be happy. 

I counted 25 members on the 6z EPS using Allegheny county as the measuring stick that give us a solid 6-8 in storm. That's an improvement over yesterday. My only concern is the last few storms the Euro seemed to be the most amped up so take that caveat how you want at this point.

Other models have also increased totals slightly for us too. Overall things trended in the right direction overnight. 

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1 hour ago, RitualOfTheTrout said:

Heh, man what a track.. Nothing like these old forecasts with big CRT monitors etc in the background.

I remember that TWC map. We had a first wave that overperformed and were sitting on like 8 or 9”. That supposed to be 12+ additional, but the big snows from the coastal cut off around somerset. We wound up with about a foot total where I was.  Pretty sure they got 3’ in Somerset 

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