Historic Christmas Cold & maybe snow?! Dec 23rd-30th

[Scottie16]

3 minutes ago, Carvers Gap said:

Say what we want about the lack of snow, but the 18z GFS is straight bringing the cold.

I don’t think any WWA will survive this front. 

[fountainguy97]

I'll be interested to see how long my inch of snow lasts with this airmass lol. 
 

Very impressive cold shot for sure.

[PowellVolz]

For a sliver of hope...GEFS mean actually had a nice little increase for the eastern valley

Baby steps


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[John1122]

Every run of every model gives me 1.5 to 4 inches ratio'd. So I'll certainly take that. 

[PowellVolz]

Every run of every model gives me 1.5 to 4 inches ratio'd. So I'll certainly take that. 

Beggars can’t be choosers


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[Matthew70]

4 hours ago, Itryatgolf70 said:

Hate to be berenger of bad news, but If we don't get a system by end of the week, at minimum we got until mid January before pattern becomes more favorable for winter weather. I'm hearing too extended EAMT event is going to happen and flood the US with warm air. 

I say bring it. Cold & dry especially this cold.  I will take a hard pass.  I’m already thinking about in 10 days we’re back to the 50’s.  With sunshine that will be nice. 

[PowellVolz]

I say bring it. Cold & dry especially this cold.  I will take a hard pass.  I’m already thinking about in 10 days we’re back to the 50’s.  With sunshine that will be nice. 

Yes.. I’d rather be playing golf than counting flurries when it’s 8 degrees outside. That’s almost as depressing as 33 and heavy rain.


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[Jesse from KY]

Hi, I just wanted to chime in and say that I've noticed the models have been delaying the ETA of the colder air on Thursday night/early Friday morning. 

I have been looking at the last several runs of the NBM (Model Blend). At 12z-18th run of the NBM for example, Somerset, KY's forecasted temp @ 1 am Friday was 29F. And as of the 00z-19th (latest) run, the forecasted temp for that same hour is 37F.
 

[PowellVolz]

Hi, I just wanted to chime in and say that I've noticed the models have been delaying the ETA of the colder air on Thursday night/early Friday morning. 
I have been looking at the last several runs of the NBM (Model Blend). At 12z-18th run of the NBM for example, Somerset, KY's forecasted temp @ 1 am Friday was 29F. And as of the 00z-19th (latest) run, the forecasted temp for that same hour is 37F.
 

If you’re looking to get your heart broken, you came to the right place.

Welcome aboard


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[Jesse from KY]

14 minutes ago, PowellVolz said:

If you’re looking to get your heart broken, you came to the right place.

Welcome aboard


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Thank you!  

[fountainguy97]

Oh she cutting hard this run. What a storm this is going to be this week.

[Dankles]

Oi, the GFS just keeps getting worse every run

[Matthew70]

Maybe this front will not make it here. I know it will but it would not hurt my feelings if this Arctic air would stay north of us.  Dry & cold I’m not interested in.  

[John1122]

The GFS has the odd snow fingers look that run.  It tends to do that with the rain to snow scenarios. Basically smooth them out and cover the blank areas between the fingers, cut the amounts by 30 to 40 percent and that's usually closer to what actually happens. 

[Silas Lang]

The LP is in Illinois on this run. It's going to be in Nebraska at this rate. lol

[Matthew70]

6 minutes ago, Silas Lang said:

The LP is in Illinois on this run. It's going to be in Nebraska at this rate. lol

I’m good with that lol.  Maybe makes this dry arctic air retreat quicker.  

[John1122]

The GEFS actually looks pretty good vs the Op. 

[John1122]

Ratio'd would be about 25-30 percent above these totals. 

[MattPetrulli]

Only interested in this for the likely high impact wind event and the cold snap. Don't care for .5 inches of snow

[John1122]

The GFS remains enthusiastic about the anafrontal prospects. We will see if if keeps it up. It hands down beat the Euro for the last several. The Euro didn't really get on board with the Christmas 2020 event until 36 hours out. 

[Holston_River_Rambler]

I can't tell if the GFS is showing a wave running the front to produce the anafrontal precip, or if it is one of those deals where the GFS still thinks there's precip after the front moves through. 

I think what we want at this point is something like Christmas 2020:

 

You can see the shortwave throwing precip back as the precip shield takes on that weird stretched S shape:

 

I went back to the Dandrige Dollop storm thread and found some of the H5 vort maps to see how that one played out. Sorry these are random snap shots of the models depiction of that storms evolution, but that was all I could find:

Euro from about 130 hrs out:

CMC from around 144 hrs out:

 

RGEM from about 80 hrs out:

Each of those has some indication of a secondary vort lobe that spawns the leeside low. 

This one is just a wrecking ball, but there are small individual vort whisps that keep some divergence after the arctic air arrives:

Euro looks less good with regards to that potential:

GFS also has us in *gasp* not the right entrance region of a jet streak, but the left exit (also favorable for upper divergence and lift):

Euro is similar, but a little further north with the jet:

Those are probably the differences in the amount of precip each model drops after the front blows through. 

 

Apologies if that was too much, but I kind of wanted to work through the what and why of the set up, so I could know have a handle on my own expectations lol. 

I like the leeside idea and want it to work since it has worked in the past (Dandridge Dollop storm, Christmas 2020), but as of now (admittedly 100 hours out) ensembles aren't too thrilled:

 

GEFS:

 

 

 

[Carvers Gap]

As many have said, a front that powerful is gonna have a ton of energy. It should churn out some precip,   In addition to the extra precip, the further west that storm gets the more of a window opens for mischief to happen along that front here.  I don’t trust the GFS as it failed miserably in predicting the location of the upcoming low.  It has moved from North Carolina to Illinois.  That said, once it locks in the track...it probably will handle the precip amounts a bit better. As others have noted above, the Euro seems to be missing precip which had been a common bias of that model in this setup.

[Carvers Gap]

I looked to see if there was a wave in the 6z GFS.  On the 700 vort map, there is a small piece of energy which is caught on the lee side of the Apps.  That could be part of it.  The other orographic lift IMO.  The jet has to be roaring above.  When that hits any amount of elevation, it is going to squeeze precip out.  But again and not to beat a dead horse, the front is so strong it is going squeeze precip on its own without the lift. 

[PowellVolz]

I looked to see if there was a wave in the 6z GFS.  On the 700 vort map, there is a small piece of energy which is caught on the lee side of the Apps.  That could be part of it.  The other orographic lift IMO.  The jet has to be roaring above.  When that hits any amount of elevation, it is going to squeeze precip out.  But again and not to beat a dead horse, the front is so strong it is going squeeze precip on its own without the lift. 

Does the cold air overrunning a warm wet ground help with lift?


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[fountainguy97]

06z gfs is actually a nice hit for many. It has MUCH more of the front as snow than euro and crew.  I remain extremely skeptical after the GFS performance with this one. I've never had fun with "cold chasing moisture" setups.  Although this is on an extreme level.

 

Ratios will be extreme. So even .2 more qpf can stack on 4+ inches.

[Carvers Gap]

19 minutes ago, PowellVolz said:

Does the cold air overrunning a warm wet ground help with lift?


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I wouldn't begin to know the answer to that.  Re: 6z GFS.  I think it is just the strength of the front, orographic lift, and the overhead jet.  It also could just be that the 6z GFS is a blip and had more precip on this run.  We will know if it is a trend soon.  It looks like the convection in the GOM gets out of the way quicker which may allow for the conveyor belt to pick up more moisture.  We have all seen the movie before...great forecast but convection fires in the GOM and cuts our qpf in half.  The lift occurs on the Plateau and a secondary wave over the eastern valley - think of a wave on the ocean where you have a peak then a valley and a secondary peak.  The other lift occurs over TRI as we are just a bit higher here.  Points east of I-81 are favored.  

[PowellVolz]

06z gfs is actually a nice hit for many. It has MUCH more of the front as snow than euro and crew.  I remain extremely skeptical after the GFS performance with this one. I've never had fun with "cold chasing moisture" setups.  Although this is on an extreme level.
 
Ratios will be extreme. So even .2 more qpf can stack on 4+ inches.

Those streamers are not shaped like the typical NW flow. Almost looks like it’s part of the cold front.


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[Carvers Gap]

I am assuming MRX probably wrote this prior to 6z...This will be remembered as one of the great pre-Christmas fronts.  We normally don't see these in December, but it does remind me very much of a couple of years ago around this time.  

 

The models are coming into better agreement on the pattern for
Thursday night and Friday, as the GFS has trended toward the ECMWF
solution of a closed low developing over the MS Valley/OH Valley
region on Thursday night, with the surface low rapidly deepening and
tracking across the Great Lakes region. This solution keeps most of
the wrap-around moisture to the north of our area, and the GFS has
backed off on it snow amounts. Confidence is increasing that this
won`t be a significant snow event.

However, the blast of arctic air into the area will still have the
potential to cause significant impacts. The GFS continues to be
slower with the timing of the cold frontal passage, showing it
occurring after 12Z Friday. But this timing is not as much of an
outlier among the NBM members as it was with previous runs. So the
forecast will slow down the arrival of cold air late Thursday night
into Friday morning, mainly between 06Z and 12Z. With this very cold
air moving in quickly, any moisture on roads from earlier rain will
rapidly freeze. This will continue to be the focus of impact
messaging for the holiday weekend.

Through Friday, strong cold advection will result in high temps
occurring in the morning, and falling through the day. Isolated
to scattered snow showers can be expected all day, with the
greatest coverage in the northern half under the upper low. Winds
will be strong and gusty behind the front, likely 15-30 mph with
gusts of 40- 50 mph. With temperatures in the teens and 20s on
Friday, and single digits Friday night, wind chills will reach
dangerously low levels, especially in the mountains.

 

[Carvers Gap]

7 minutes ago, PowellVolz said:

Those streamers are not shaped like the typical NW flow. Almost looks like it’s part of the cold front.


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Yep, that looks like an ana front signature.  You can also see where the elevation is in TN.  NW flow develops the next day.  WB must be more smooth than Pivotal.

[Carvers Gap]

Addendum...that map is heftier due to upslope which follows in the 24 hours after the front.  Many areas north of I-40 pick up 1-2" more in the bitterly cold air that the precip falls into.