January 2021 Medium/Longterm Pattern Discussion.

[John1122]

3 minutes ago, Carvers Gap said:

Something has changed in modeling for that many global models to all of the sudden reach agreement.  My guess is that modeling has not caught up to this storm - trends could obviously be better or worse!  LOL.  We will certainly take a good 12z suite of operatonals though!

The timeframe has a +PNA/-NAO/-AO at a level not seen in combination since the first half of February 2010. There were 3 snow events from Jan 29th to February 15th that year. 

[Carvers Gap]

Just now, 1234snow said:

Agreed. I’m not sure I’ve seen every single global model latch onto a similar solution in one run before.

12z GFS, EURO, CMC, ICON, UKMET all have a similar solution with someone in NE-TN/mountains/NC/SWVA getting accumulating snow.

Even the ACCESS-G (Australian) has a pasting for the mountains. Yes, I just found that model haha.

I hadn't even planned on watching much of the 12z run until I saw the 12z ICON posted in the MA forum.  The CMC has had it for a few runs kind of off and on, but just tough to believe it at times.   That said, the CMC has done really well this winter with systems in this region.  But yeah, something had to have changed to get that abrupt of an agreement.   Might just be that models are converging on a solution - but not sure on that.

[Carvers Gap]

4 minutes ago, 1234snow said:

Agreed. I’m not sure I’ve seen every single global model latch onto a similar solution in one run before.

12z GFS, EURO, CMC, ICON, UKMET all have a similar solution with someone in NE-TN/mountains/NC/SWVA getting accumulating snow.

Even the ACCESS-G (Australian) has a pasting for the mountains. Yes, I just found that model haha.

LOL.  Yeah, you are digging deep if you are dialing up the Australians!  

[Carvers Gap]

3 minutes ago, John1122 said:

The timeframe has a +PNA/-NAO/-AO at a level not seen in combination since the first half of February 2010. There were 3 snow events from Jan 29th to February 15th that year. 

Yeah, the 12z GEFS has a beefy snow mean for the central and NE valley along with the Plateau.  Been creeping up since 0z.  

[Carvers Gap]

Well, that was a pretty wild run of the 12z Euro.  Yet, another storm is in the pattern around 180.  

[Carvers Gap]

Definitely western areas of the forum would also want to give that a look.  Big changes with the 12z suite for sure.

[Carvers Gap]

Not to be overlooked, but the LR pattern has a -EP ridge, -NAO, and BN heights in the Bering Strait on the 12z GEFS....that model is decidedly colder than two days ago with BN temps during week two through much of the nation's mid-section and eastward.  12z GEPS looks good as well.  

[tnweathernut]

What I take from the looks on modeling and ensembles over the last couple of days..........

Many of us are likely to be dog tired after the next 2-3 weeks from tracking multiple systems. Normally I wouldn’t be so bold, but the pattern shown is screaming multiple opportunities.  Could we strike out?  Sure, this is the Tennessee Valley region.  Is it likely?  I don’t think so.  Buckle up.

[Carvers Gap]

Also, be sure to look at the NA view of the GFS on Tropical Tidbits.  Toggle to temps(not anomalies) and watch the cold come over the pole into Canada.  Impressive.

[Holston_River_Rambler]

Yeah the 12z Euro was nice for many parts of the state: 

[Carvers Gap]

So, looking at the 12z GFS and Euro, sure looks like the TPV splits just by the  cold that some this direction.  If you look at the 50mb strat anomalies on the GFS, you can see a significant split. The TPV is very likely under the warmer heights heading over the pole after d10 on the operational run.

[Carvers Gap]

You can watch on both the GEFS and GEPS at 12z, the cold just pouring over the pole once the GOA vortex(which pumps the cold back to Siberia initially...see previous posts) gets out of the way.   The 12z GEFS is very much in the process of relocating a large portion of Siberian cold over the pole once that GOA vort gets out of the way after next weekend.

[John1122]

Some -12c to -14c BN anomalies at 850 showing up on the EPS.  Those showing up in mid January would mean some extremely cold weather at the surface.  Probably closing in on 0. 

[nrgjeff]

Track issues aside, I'm encouraged to see Chattanooga thickness 540 or below when or shortly after precipitation starts with both systems. In January (vs March BL questions) 540 ought to be cold enough. That's only good news farther north and west along I-40 (BNA, MEM?) and especially northeast. It's tricky in Huntsville. What's new for HSV and CHA?

Appears that cold air tries to get in place before both systems. Big upper ridge in eastern Canada helps deliver the surface highs. Then there are 50/50 lows; honestly, I hate that expression. 50/50 is worthless in a mild stormy pattern. However next week proper ridging is forecast in eastern Canada.

Also for a wider swath of snow we need that Western US ridge to verify; and, not let any energy sneak through the Desert Southwest and Southern Rockies. Diving down the Plains and sliding across the Deep South is what we seek.

Southern stream energy caused the Georgia tornadoes. Though the synoptic low went through the Midwest, southern stream energy and trough did Georgia. Now, do it with cold in place. Past performance blah blah blah.

Main takeaway: I always like 540 thickness. The old fashioned method is sweet news to me - esp mid-winter.

[PowellVolz]

The timeframe has a +PNA/-NAO/-AO at a level not seen in combination since the first half of February 2010. There were 3 snow events from Jan 29th to February 15th that year. 

And it was brutal cold. Knox Co school was out for 2 weeks.


.

[Carvers Gap]

18z GFS gets strung out with the storm on the 8th.  However, the 18z GFS-Para now has it.

[Carvers Gap]

The 18z GFS does continue the trend of 12z modeling in finding bitterly cold air after d10.  So as not to create confusions.  The GOA vortex still basically pumps the cold out of northern Canada during the next week.  Post d10, the steady reversal of cold back over to the pole into Canada is still there...but vastly accelerated.  I think a new/continued SSW is playing a role that.

[Vol Man]

Robert mentions the possible storm at the end of the week...

WxSouth possible storm

[jaxjagman]

it's happening

 

 

[Carvers Gap]

28 minutes ago, jaxjagman said:

it's happening

 

 

Good catch.  And the changes due to that may be very abrupt.  Modeling is a lot colder today.  Very evident the TPV is getting split after d10 within those runs.  Seeing models change over the last 48 hours reminds me of Feb’18.

[John1122]

GFS not so good, Canadian a good bit better with system one. GFS shifts 500 miles with system two and decides it's going to be a big cutter even with a massive amount of blocking over the top. AKA very unlikely outcome.

[John1122]

Canadian feels the block and the second system is a deep south slider from Texas to South Carolina. Huge difference between it and the GFS.

[John1122]

Euro looks like the GFS almost with the first storm. Perfect track but just doesn't really blossom precip other than a couple of random spots that get heavy snow, then it nails NC. The second system is a classic Miller A/Slider that also appears to have an underdone precip field. It's been discussed many times over the years how poorly models depict precip fields with Gulf lows.

[John1122]

06z GFS looks like it's going to Miller A storm 2 like the Euro. 

[John1122]

Perfect track, light precip, much warmer than the Euro/Canadian.  See the prior post about models struggling mightily to handle Gulf Low precip shields. 

[John1122]

We get a perfect track Gulf storm that drops .20 or less QPF over a 12 hour period. Also a good part of the area have favorable 850s, 540 thickness, plus it's overnight but it shows rain on the model output. Seems unlikely with that storm track and those upper levels. I figure there would be heavier precip, more top down cooling and a much better chance at snow. 

The GFS is by itself for now on those thermals. 

[Holston_River_Rambler]

Overnight UKMET:

 

Maybe it just sees the snow as 4:1 ratio type stuff as it falls over most of TN?

]

 

 

[Holston_River_Rambler]

MRX mentioned a subgeostrophic jet streak in their overnight discussion and I thought it was kinda cool that the NWS explanation for jet streaks: 

https://www.weather.gov/source/zhu/ZHU_Training_Page/winds/JetStream_Stuff/300_200_chart.htm 

is similar to what what the Euro is depicting for the Jan 8 - 9 system:

 

     

 

 

 

 

[Carvers Gap]

Still think the 8th/9th system is just now coming into focus.  Trends tend to favor western NC, but really tough to rule out the eastern valley at this point or even the Plateau.  Another system is immediately after that one centered around next Monday.  The 6z GEFS mean for NE TN is 6+" of snow w/ 2-4" for much of middle TN and the rest of E TN - increasing as one heads north and east.  

[Carvers Gap]

3 hours ago, Holston_River_Rambler said:

Overnight UKMET:

 

Maybe it just sees the snow as 4:1 ratio type stuff as it falls over most of TN?

]

 

 

The one thing with the 8th/9th systems is the downsloping in the eastern valley.  The system is weak enough and far enough away that some downsloping (and even temps rising) is possible over the far eastern valley including portions of TRI.  Seems like when modeling latches on to downsloping, tough to shake.  12z suite about to roll...