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16 minutes ago, Chris78 said:

I know there's some doom and gloom this morning but the precip that slides just south of us is very impressive. As long as we Do Not lose ground to the south over the next few days I think we'll be ok. If we get out normal north bump over the final 36 hours it would be a real nice event. The 12/9 Event had the northern extent in southern va at one point and moved significantly north over the last 36 hours. @psuhoffman  always talks about not losing to much ground to the south prior to the eventual north trend and I think this may be the case here.

gfs-ens_apcpn_us_22.png

90% of synoptic systems in our area adjust north with the northern extent of the snowfall the last 36 hours or so. It used to be 72 and a much bigger adjustment but it seems guidance has improved itr. But still the final 36-48 hours 9/10 times it adjusts north about 50 miles or so. That's not going to help if the northern edge is richmond 48 hours out.  But if we're still sitting close like now that would bode well.  

This isn't universal though. March 2014 the first storm trended south right until the end as guidance was too far north with a lobe of the PV pressing down and as that trended south the system trended weaker and south each run right to the end. So that can happen especially if a storm is washing out not amplifying as it comes east. This has some of those characteristics but a much less supressive flow on top than the 2014 example so the outcome is murky. 

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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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2 minutes ago, DCTeacherman said:

Pretty significant drop from yesterday 12z when the 0.5 line was up near PA but still keeps us in the game for a light/moderate event.

True, seems the CIPS outcomes are not happening now,  as a stronger system with phasing is unlikely, but as psu stated getting things to move North in the last 36 hours may be doable.

I like DC better than my location, but maybe a couple inches would still be nice up this way. 

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1 minute ago, osfan24 said:

I think sitting in this position is fine if the trajectory is going to get it to climb the coast. The problem is this looks more like a west-east system and a southern slider type, so I'm not sure we will see the north adjustment at the last minute.

We need some interaction with the NS to pull it up the coast... otherwise it is a light event with a whiff to the south.

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15 minutes ago, DCTeacherman said:

Pretty significant drop from yesterday 12z when the 0.5 line was up near PA but still keeps us in the game for a light/moderate event. 

I like that the .25 line is well up, into pa. Gives us some breathing room for atleast a minor event.

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One thing to be careful for those relying on the extent of the very light precip on the north side...there are a couple ways that could fail quickly.  One is if the light snow associated with the northern stream impulse runs out ahead and goes primarily north of us.  That is the "snow into PA first" thing Ji talked about.  Then if the STJ is weak and stays south...we get split.  We do that very well.  The other is if the system is consolidated but comes out weak and washes out.  At a certain point if the system is too weak there wouldn't be enough southerly flow to create the WAA lift needed to get that light precip and the whole northern part can just become some clouds and flurries all of a sudden...and everyone would be like "where did all that precip go".  It's not like the northern edge up in central PA has to trend 100 miles south...that whole area of precip might just not exist if the system trends weaker and there isnt enough lift to create it.  

This is not mean as a doom and gloom post, I am not saying that will happen, but I keep reading posts saying we have a lot of breathing room because of that and I am not so sure that is true.  

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33 minutes ago, 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

The exception to the trending theory though is the strength of the SW. That has been a big question mark and simply put a weaker wave will have a tendency to stay south with the confluence it’s fighting against. Disagree?

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Just now, jayyy said:

about to get NAM’d.....

we’re nearly 4 days out. Having the storm bullseye VA is perfectly OK guys!

Not every storm heads north at the last second as you know.  The SS is weak sauce so no help there. 1041 is strong and dry and like a blowing on a hot cup of joe it will take the steam off the top.  Where the top of the cup is seems to be the big question.  No steam no snow.  

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We are kind of in the time frame I hate right now.  Some have noticed I post a lot in the long range, and then a lot once a storm is inside 48 hours, but there is kind of a dead period in between.  That is because at long range we are just analyzing patterns.  Looking at vague generalities of what longwave pattern we want to get a threat for snow.  But once we get inside 7 days and there is a specific threat, small details within the longwave pattern like the exact location and strength of a vort, the location of a High, amplitude of the STJ, exact slp track, NS flow to our north/suppression...all become important and NONE of them is modeled that accurately to be confident in anything.  There are rare examples where a stable blocking pattern is in place and those features are pretty much locked in by an anomalously stable longwave pattern but that is not the case now nor is it the case 99% of the time.  In these cases...we can kid ourselves each run in the medium range but the truth is we don't know and no one else does either.  Every run some of the features that will determine our fate will shift around in the guidance and we can make educated guesses and lean on the "better" guidance and historical references and all...but in the end none of us knows.  So I sit back and wait for some clarity to emerge.  Once we get inside 48 hours and those details are mostly figured out it gets fun again for me when we can see how the system is evolving in real time and I can start to get a feel for meso scale things like banding and convection and nailing down the details in the storm.  That is the real fun part for me.  This in between time is frustrating more than anything else.  But that is why I often don't post as much in the day 3-6 range as I do long range and short range...its not that I don't see the threat or like/dislike it... its just annoying getting too worked up over each run when it can and often does change the very next run. 

But pertaining specifically to this threat, it is not the kind of threat that is locked in by a stable pattern, we are in a progressive pattern that is in flux right now during an overall longwave pattern change...the setup is pretty good overall and could work out but has flaws.  I don't like how the trough is deamplifying as it comes east.  We need that vort to be stronger and eject in one piece to overcome that.  Guidance is jumping around with that detail so how anyone can feel too confident one way or the other is beyond me.  We are getting close to the leads where that should come into better clarity though.  Maybe today.  

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36 minutes ago, psuhoffman said:

90% of synoptic systems in our area adjust north with the northern extent of the snowfall the last 36 hours or so. It used to be 72 and a much bigger adjustment but it seems guidance has improved itr. But still the final 36-48 hours 9/10 times it adjusts north about 50 miles or so. That's not going to help if the northern edge is richmond 48 hours out.  But if we're still sitting close like now that would bode well.  

This isn't universal though. March 2014 the first storm trended south right until the end as guidance was too far north with a lobe of the PV pressing down and as that trended south the system trended weaker and south each run right to the end. So that can happen especially if a storm is washing out not amplifying as it comes east. This has some of those characteristics but a much less supressive flow on top than the 2014 example so the outcome is murky. 

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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Be careful with "trends" because mathematically its a myth.  Each run is a singular run.  If there is a trend it is just because the guidance keeps making the same errors in continuous runs but that trend can reverse itself the next run (like 0z last night after the trend towards more amplification the 2 runs before that).  

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3 minutes ago, 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. 

   

Not necessarily related, but did you see Cranky's new discussion on Twitter? Its quite good.

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2 minutes ago, psuhoffman said:

Be careful with "trends" because mathematically its a myth.  Each run is a singular run.  If there is a trend it is just because the guidance keeps making the same errors in continuous runs but that trend can reverse itself the next run (like 0z last night after the trend towards more amplification the 2 runs before that).  

Sounds like Dr Spock, very logical ! 

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4 minutes ago, psuhoffman said:

Be careful with "trends" because mathematically its a myth.  Each run is a singular run.  If there is a trend it is just because the guidance keeps making the same errors in continuous runs but that trend can reverse itself the next run (like 0z last night after the trend towards more amplification the 2 runs before that).  

I agree. I never mentioned a trend. Simply pointing out the idea of some snow showers Saturday night followed by a dry period and then maybe getting the Coastal to gain enough latitude to hit us. This would be different than what is currently modeled as more of a drawn out long duration light event. 

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