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January 12-14, 2019 Storm Threat

WxUSAF

By WxUSAF,
in Mid Atlantic

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psuhoffman

psuhoffman

Posted
Posted
  On 1/9/2019 at 2:36 PM, frd said:

Have a question for you and this relates to a post about an hour ago by @bluewave in the NYC forum. He makes a good point, and has touched on this point a couple times the last week, stating the Pac jet is so fast it is causing issues,  and we are lacking the typical STJ, that you tend to see with Ninos.

I know we were talking about the TPV , phasing and confluence as factors here with the weekend storm, but is not the fast Pac also a limitation on the pattern producing ? ( effectig SWs in the flow , not allowing amplification and other issues )    

And if so, I imagine we see that hopefully change when the new pattern fully establishes itself later in Jan. 

Even Earthlight     https://twitter.com/jhomenuk  states that we are only at the start of an improved pattern, as we move out of the crap we had to endure. 

   

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I think the fast Pacific jet is wreaking havoc with the guidance and has been responsible for the tanking verification scores at times lately.  The more you speed everything up the more chaos you create.  And in general its not going to help with amplification.  I do think the fast pac flow crashing the west coast could be compressing the longwave pattern over NAM and leading to the deamplification of the trough as it comes east.  But we have had some pretty good snow events out of this type of setup before also.  I don't think the pac jet along is fully to blame.  If the vort comes out stronger and in one piece we will be ok.  The pna ridge out west is somewhat muting the effects of the pac jet right now just enough to allow this threat to sneak in during the pattern transition.  

Long term I agree as the pacific jet relaxes and we establish more stable ridging out west and cut off the influence completely our chances will increase.  Our biggest threat to a snowstorm in the long range seems to be more related to the blocking pattern on the Atlantic side and exactly how the block/PV sets up and situates themselves.  Not saying that is a big problem right now...but a bigger risk in the pattern showing up in the long range than the pacific.  

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Ralph Wiggum

Ralph Wiggum

Posted
Posted
  On 1/9/2019 at 1:55 PM, MD Snow said:

Anybody else seeing that both the GFS and ICON seem to holding things back a bit. Their 6z runs now bring the SLP up to Hatteras between hrs 114 and 120. ICON has been hinting at this. Will be interesting to watch. This would support the idea of maybe a front end WAA Saturday night, a dry period and then getting hit by the coastal Sunday afternoon. Something to watch for today. 

 

For instance, here's the GFS at 0z and then 6z. 

 

gfs_mslp_pcpn_frzn_neus_fh114_trend.gif

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See my earlier post....IcON was setting up for a later possibly more robust system Monday.  Delayed but not denied??

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frd

frd

Posted
Posted
  On 1/9/2019 at 2:49 PM, psuhoffman said:

Our biggest threat to a snowstorm in the long range seems to be more related to the blocking pattern on the Atlantic side and exactly how the block/PV sets up and situates themselves.  Not saying that is a big problem right now...but a bigger risk in the pattern showing up in the long range than the pacific.  

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Thanks psu, we do need the Pac jet to relax.

And, what you said here at the end echoes @showmethesnow thoughts about the evolution of the PV near Hudson Bay, and how it proceeds will effect storm oppurtunities for us here, specifically how far South it drops later in the month and in early Feb. 

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psuhoffman

psuhoffman

Posted
Posted
  On 1/9/2019 at 2:49 PM, Ji said:

well we are never to trust the NAM between 60-84 no matter what is shows...maybe its rearing to crank up a coastal like the ICON on monday

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If the guidance trends towards holding more back that actually does become a viable option...but more often then not when you get a split like that what ends up happening is the "in between" option which screws us.  We had such a solution last January...lead wave brought a very light snow event (like 1")...but better north of us...then the energy that held back formed a trailing low down in NC and gave them 3-6" but we were stuck in between.  Sometimes if enough is held back something can ride the coast in that kind of setup but its rare.  

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cae

cae

Posted
Posted
  On 1/9/2019 at 10:22 AM, Ji said:

Ensembles are pretty much useless. None shut us out but this is exactly what happened

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  On 1/9/2019 at 11:57 AM, leesburg 04 said:

So as novices we sit here and look at the ensemble runs from yesterday and see gobs and gobs of snow and now those same ensembles show the above. Raisins in cookies that look like chocolate chips or a trainer that says one more rep then adds another and ensemble runs are why I have trust problems

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  On 1/9/2019 at 11:58 AM, psuhoffman said:

Ncep is aware the gefs aren't dispersive enough.  Hopefully they fix it soon. 

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What PSU said.  It's mostly a problem with underdispersion in the GEFS.  I know a lot of people here know this, but for those who don't:  that means that the GEFS members have more "groupthink" than in other ensembles, and they tend to cluster around the GFS.  So if the GFS says we'll get a big hit, we can expect to see a lot of GEFS members agree.  And if the GFS says we won't get a big hit, a lot of GEFS members will probably agree with that as well.  Long-range op runs (like the GFS) tend to jump around a lot from run to run, and ideally an ensemble should be steadier.  But because it follows the GFS so closely, the GEFS also jumps around quite a bit.  So following the GEFS leading up to a potential storm can feel like an emotional roller coaster.

One of the reasons I follow the Canadian ensemble is because it is more disperse.  You can see this in the below maps from last night's 00z runs. The way to read these plots is that the red numbers correspond to the centers of low pressure in the different ensemble members.  The shading of the plot indicates how much spread there is in the ensemble members.  Darker blues mean the ensemble members agree with each other more, and lighter blues and greens mean there is less agreement.  The image toggles between the GEFS (GFS ensemble) and GEPS (Canadian ensemble).  You can the tight cluster of lows off the coast of NC in the GEFS, and the broader spread of low pressure locations in the GEPS. 

52TclUQ.gif

The dispersion makes the Canadian enesmbles less exciting, but I find that it also gives me a better sense of how likely it is for things to go wrong.  A slight red flag from last night was that the Canadian ensemble stopped getting better.  Typically, leading up to a big storm the Canadian ensemble will gradually improve as the members come to agreement that it's going to snow.  But in both the 12z and 00z runs yesterday, only about 1/2 the members showed more than 1" of snow for me.  On the other hand, although the 06z GEFS run was not a good sign, I wouldn't worry about it too much unless it gets broader support from the other ensembles and ops.

As PSU mentioned, NCEP is aware of the problem with the GEFS.  Unfortunately, from what I understand, it might not be fixed until the FV3 ensemble is in place in 2020. 

 

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psuhoffman

psuhoffman

Posted
Posted
  On 1/9/2019 at 3:09 PM, AfewUniversesBelowNormal said:

It's been so moist though, it's hard to believe even in the option where the energy becomes split it doesn't trend wetter, with 500mb closed off way back in Colorado. 

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The problem is that the upper level flow is compressing and deamplifying as it comes east.   If the system is consolidated and amplified enough to hold together to the east coast where it would have a chance to amplify again based on lower level baroclinic forces then it could work but if its weak and strung out it might wash out before getting here and then redevelop too late for our purposes.  

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LP08

LP08

Posted
Posted
  On 1/9/2019 at 3:20 PM, yoda said:

One would think that the 12z ICON should come north some based on h5 at 78 -- looking at the s/w in the NE moving NE some compared to 06z at 84, which results in slight height rises in the east

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It's a good run with widespread totals of 3 to the north and the heaviest stripe from Central VA south to the boarder.

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psuhoffman

psuhoffman

Posted
Posted
  On 1/9/2019 at 3:15 PM, cae said:

As PSU mentioned, NCEP is aware of the problem with the GEFS.  Unfortunately, from what I understand, it might not be fixed until the FV3 ensembles are in place in 2020. 

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Unfortunately it's not an easy fix, and probably isnt cost effective for them to fix the old ensembles if they are currently in the process of developing a new system based on the FV3 operational.  Of course if the rumors that the FV3 has been disappointing and they might not switch over for a while are true that complicates things.   I would be interested in knowing if the issues are just because the FV3 is new and needs some minor adjustments or if they are now doubting its viability as a replacement to the GFS.  

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