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

[McMinnWx]

Oh, hi 6Z GFS. 

[John1122]

06z GFS has pockets of very heavy snow being depicted behind the front now with almost all of the precip with it being anafrontal. Very little rain out ahead of it. Very similar to Christmas 2020.

[Holston_River_Rambler]

One of the GFS soundings is pretty awesome in one of the pockets of heavy snow (this one near Monticello KY):

11000' DGZ fully saturated. 

[Holston_River_Rambler]

Thought I'd check out the Euro soundings to see how it is handling the airmass after the front and I think it gave me a new weenie rule!

If the sounding shows the dewpoint being higher than the air temperature, something could be off with the way the model is rendering that particular area:

[Jed33]

6 minutes ago, Holston_River_Rambler said:

Thought I'd check out the Euro soundings to see how it is handling the airmass after the front and I think it gave me a new weenie rule!

If the sounding shows the dewpoint being higher than the air temperature, something could be off with the way the model is rendering that particular area:

Yeah, something might be off there, it is not possible for the dewpoint to be higher than the temp. Or put another way, the temp cannot drop lower than the dewpoint. (Fully saturated if they are the same value) The temp and dewpoint can lower at the same time but the lowest the temp can go is the dewpoint. 

[Holston_River_Rambler]

1 minute ago, Jed33 said:

Yeah, something might be off there, it is not possible for the dewpoint to be higher than the temp. Or put another way, the temp cannot drop lower than the dewpoint. (Fully saturated if they are the same value) The temp and dewpoint can lower at the same time but the lowest the temp can go is the dewpoint.

It could just be the way pivotal rendered the sounding, but thought I'd look under the hood to see what the Euro saw differently from the CMC and GFS. 

[Knoxtron]

Man these temps/windchills are scary

Sitting at 2100' Elevation north of Soddy-Daisy I really don't know what to expect haha

[fountainguy97]

There is really no major difference in qpf between euro and GFS. The GFS has the bulk of precip falling behind the 32 line will EURO has it in front. 
 

for now the RGEM/NAM seem to favor the gfs although I'm skeptical of meso models until inside 48hrs.

[Jed33]

I remember when the official windchill values were changed to supposedly make it more “accurate”. They raised the values, making it harder to achieve cold windchill readings. Back in the 80’s those numbers would have been even colder than that

[Carvers Gap]

9 hours ago, Jed33 said:

Use caution because it is the CMC, it did look ever so slightly better for the pre-Christmas storm, but look at Tues! That is how you get a clipper to hook up with the Gulf of Mexico, spawn a low pressure, and make a powerful winter storm!

That system is strong enough to bring some warm nose issues up into the eastern valley though, more of a snow to sleet/rain mix and back to light snow at the end. Middle and West TN, North MS and AL fare better than east TN but East TN does ok with it

The CMC has been verifying higher than the GFS and Euro at d10+.  Several times it has had a correlation coefficient of 0,8 or more.

[Carvers Gap]

It is important to remember that wx models are tools much in the same way carpenter’s use tools such as hammers or squares or levels.  Whether they are used accurately is up to us.   
 

On to the ex...The 6z Gfs isn’t budging and is a true anafront where - the precip is behind the front.  While I don’t trust that model, the Euri struggled with this setup a couple of years ago if I remember correctly.   I don’t trust it either.  think part of the issue is tracking storms from ten days out.  There are 40 different runs(one just one operational model) but ultimately one verified reality.  I think a blend of modeling is not a terrible idea at this point.    

[Carvers Gap]

While modeling has struggled w slo placement, they have been incredibly accurate from d10+ re: temps.  

[Carvers Gap]

One thing I am noticing is that the actual cutter is barely a cutter.   I could be wrong(wouldn't be the first or last times), but it looks like a northern system  w/ a cold front.  The snow amounts in the Mid-west and eastern Plains have diminished remarkably.  Not sure that changes the overall solution, but that is looking like an error(too strong) by all global models.

[John1122]

The GFS looks like it's going full on clipper here with the LP moving SE.

[John1122]

Well the GFS drops SE than goes almost straight north as it strengthens. Still keeps the idea of being a nearly all anafrontal event.

[John1122]

You're unlikely to ever see a low take that track that it does on the Canadian and have such a small precipitation shield. That's a big winter storm track for the Eastern half of the state especially.

[tnweathernut]

25 minutes ago, John1122 said:

You're unlikely to ever see a low take that track that it does on the Canadian and have such a small precipitation shield. That's a big winter storm track for the Eastern half of the state especially.

Agree, as shown it's a strengthening storm, but the precip shield doesn't match.  With that track, you'd think the north/northwest precip shield would be a bit more robust.

 

[Carvers Gap]

The system on the 23rd (in the Midwest and eastern Plains) is a shell of its former modeling self.   I am not sure I classify that as a cutter as no energy really cuts.  That is a northern stream system which means the problem we fight is that it goes to shallow as at the even nears.  This systems has gone from Miller A to hybrid to blizzard cutter to as John notes...almost a clipper (if I am reading that correctly as we are talking two storms now in this thread).   

As for the second system...not sure.  The GFS and CMC handle in a completely different manner...one is a clipper and one is a Miller A.  

For the sake of clarity, I probably will move future comments about the "maybe" system on the 27th back to the pattern discussion thread.  If it becomes anything, might worth a thread of its own.

[John1122]

8 minutes ago, Carvers Gap said:

The system on the 23rd (in the Midwest and eastern Plains) is a shell of its former modeling self.   I am not sure I classify that as a cutter as no energy really cuts.  That is a northern stream system which means the problem we fight is that it goes to shallow as at the even nears.  This systems has gone from Miller A to hybrid to blizzard cutter to as John notes...almost a clipper (if I am reading that correctly as we are talking two storms now in this thread).   

As for the second system...not sure.  The GFS and CMC handle in a completely different manner...one is a clipper and one is a Miller A.  

For the sake of clarity, I probably will move future comments about the "maybe" system on the 27th back to the pattern discussion thread.  If it becomes anything, might worth a thread of its own.

I've been including it here since the thread covers the winter threats from Dec 23rd to 30th.

The Euro was closer to the CMC but very suppressed at 0z I believe.

[Carvers Gap]

19 minutes ago, John1122 said:

I've been including it here since the thread covers the winter threats from Dec 23rd to 30th.

The Euro was closer to the CMC but very suppressed at 0z I believe.

So the 23rd system is now acting like a clipper?  (Referencing the comment above). I actually agree with that if so.

[PowellVolz]

We ain’t gonna know anything until it happens it seems.


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[John1122]

2 minutes ago, Carvers Gap said:

So the 23rd system is now acting like a clipper?  (Referencing the comment above). I actually agree with that if so.

It definitely looks like it on the GFS.  Looks like it moves SE then back north across the Ohio Valley.  You rarely see them attached to this potent a cold front. This is basically as Siberian express. Probably not as severe as the 1982 version though.

[Carvers Gap]

Just now, John1122 said:

It definitely looks like it on the GFS.  Looks like it moves SE then back north across the Ohio Valley.  You rarely see them attached to this potent a cold front. This is basically as Siberian express. Probably not as severe as the 1982 version though.

Very much agree.  

[Carvers Gap]

Which to me means we are tracking an ana front as John noted and not a Plains/Midwest blizzard.  I think the Siberian Express is a better term.  There is some rotation over the Lakes, but this is a cold front blasting through.  That changes things some.  Now, the question is when/where the cold is...in relation to a front and not a strong SLP charging into Illinois from TX which would be cold chasing rain most likely.  I like the GFS solution.

[PowellVolz]

It definitely looks like it on the GFS.  Looks like it moves SE then back north across the Ohio Valley.  You rarely see them attached to this potent a cold front. This is basically as Siberian express. Probably not as severe as the 1982 version though.

Doesn’t it make more sense for the clipper to follow the front as it pivots around the flow?


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[John1122]

Looking at the vort maps, the 500mb vort takes a similar path on the Euro/CMC/GFS it's just much more consolidated on the GFS and dips slightly further south.

[Carvers Gap]

15 minutes ago, PowellVolz said:

Doesn’t it make more sense for the clipper to follow the front as it pivots around the flow?


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Yes.  Which is why the second system on the 27th makes sense.  

[Carvers Gap]

The Euro at 168 is much more potent on the 500vort map.  That has trended much stronger though the surface doesn't reflect that yet.

[Carvers Gap]

The 12z Euro just about got to 12z CMC levels at 500 where it turned neutral and then negative.  Something to watch for sure.  I think the system on the 23rd being weaker has allowed room for the development of a system on its heals.....the gradient is still in place versus being sharpened up.

[brianc33710]

6 hours ago, Carvers Gap said:

The CMC has been verifying higher than the GFS and Euro at d10+.  Several times it has had a correlation coefficient of 0,8 or more.

I know last night the CMC showed the area having sub 15F/-9.5C for nights on end. I started a feed in the SE forum. I couldn't find 1 so I started 1.