Winter Speculation 17/18 -December Thread

[Carvers Gap]

Hopefully the Weeklies are correct about cold returning after Christmas. This casts exceptional doubt on that idea. The trough, while not unprecedented, is in an odd configuration.  It basically slides under the PNA ridge.  It is so positively tilted that it creates a mega SER which would create a very warm Christmas week for most. Below is Christmas Day on the 0z EPS.  That trough near HI argues that the SW cold should be kicked out.  But the GEFS has it as well.  This pattern would make western areas cooler than eastern areas....but would essentially force the snow into the Plains.  Wish I had better news this AM.  I hope it is a blip, but both models have this configuration.  IMO, it is the duration of this mid continent trough that is the question to be debated, not if it happens.  Is it simply going to roll forward into the East or is that a new pattern?  I am 50/50.  The only positive I can see is if the models are underestimating how far low level cold can penetrate into portions of the forum area.  This has ice written all over it for portions of the eastern Plains and snow to the north of that boundary.  Sometimes models miss low level, Arctic cold.  My hunch is that this is more than a blip.  The GEFS now is weighted in my mind with equal importantce to the EPS.  The GEFS sniffed this pattern out and held to it for the most part minus a hiccup.

[Kentucky]

that se ridge is nasty enough, I want no part of the upgraded mega ridge

[tnweathernut]

Good disco, everyone.  Enjoy reading Jeff, Carvers, & others....

Most modeling is now showing a SE ridge.   I am not saying this is one of those times, but I remember a few winters ago (I'm getting old, may have been more than a few) modeling kept trying to stick a SE ridge in long range modeling that never really came to fruition. If I remember correctly, it was a year where we had a stout, long duration -EPO. 

Some semblance of a SE ridge can help western areas of our forum, but makes it really hard for eastern areas of the forum when it comes to wintry weather.   Low level cold can win the day on occasion, but who wants an ice storm?  With the configuration being shown on modeling we really need something to break the tie.  A -NAO would probably pull it off, but I don't see one at this point.

Another way we could potentially "win" would be to have a leader/follower situation or to have multiple disturbances over a week+ long period where each disturbance traveling through pulls the height field further south and east with time.  We'd probably have to endure a couple of rainers first, but it's possible the SE ridge would be pushed far enough to the south and east that the TN Valley region would have a shot at a more wintry solution with the final piece of energy.  

One thing I can say about the upcoming weather is it doesn't look boring (to me).  I find it infinitely more intriguing than some of the recent past years where modeling was showing warmth, warmth, and more warmth. 

Lastly, I will say we need some rain!  It's actually been quite dry for the last several months in northeast TN.  We could definitely use some wet/soaking systems and I'd welcome them with open arms.

[Carvers Gap]

Great post by tnweathernut.  Sometimes I miss the forest for the trees.  Check out Nina climo and compare it to the last map that I posted above.  Look similar?   I do agree that the models may be missing how far the cold may penetrate.  Some GFS runs had some huge highs.  And I do remember a winter where the HPs in the Plains were massive and pushed just far enough.  They were like 1040+.

[Carvers Gap]

Bastardi states that the trough stuck in the West should come out.  Stated that the cold in the northern Plains could possibly be strong enough to push into the SE.  Thinks it will correct.  Stated cold will be in the Plains but spread southeast.  Stated that the -EPO ridge should force that cold into the SE.  Now, some of that talk is because his cold Christmas idea may be on the ropes.  But I have said before that the trough axis over NA has an odd look by leaning so positively.

[Carvers Gap]

Here is also a correction.  What looked like a big PNA ridge to me is more accurately a -EPO ridge.  Here is a graphic from WxRisk's page.  It may be that the ridge is spitting the two regions.

[Carvers Gap]

The 12z GFS just destroys any idea of what I have of teleconnections.  Basically, the lack of a -NAO I get.  But the -EPO being undercut by Arctic air and then the lobe breaking off under the ridge  out West and then not moving.   I can't explain it.  It may be real.  Last January had some things that did not seem possible with the trough axis(or the winter before).    Edit...There is a Bermuda HP on that run. 

[nrgjeff]

No sugar coating the Total Disaster on the models overnight. Indeed the classic PNA is absent in favor of classic EPO. For the PNA Hawaii is backwards, as noted on the previous page. PHNL forecaster discussion notes the deep trough and incoming dews in the 50s. Wow! Disco also notes a piece cuts off; more later. 

Carvers realism is valid, but I still like some WeatherNut optimism. First the Euro weeklies have the surface cold undercutting 500 mb flow. Sometimes 850 mb does too, which is good because ice is almost as bad as cold rain. Second, I want to see another 12-36 hours of NWP for the change. Third, timing issues are normal. Last cold shot was delayed, before moving faster, and then dropping snow all across the Deep South. Fourth, my original thinking was cold after Christmas, not right on Dec. 25th, anyway.

Finally, ensemble clusters break-down reveals 25-33% are still cold here in the 11-15 day, especially late. While cherry picking single members strongly annoys me, minority clusters can be useful. We just came off a cold forecast, including the Euro weeklies. Could the warm change just be a wiggle? Remember that cut-ff near Hawaii, and how models stumble over cut-offs. Same charts tomorrow, and of course my thoughts will turn to Christmas severe.

Just kidding, not going to happen with a positive tilt to everything. So, my forecast is of course warm in the 6-10 day. I like a Plains/Texas blue norther in the 11-15 day, with cold oozing east toward us right after Christmas. I keep a cold 16-20 day including for New Year's football.

Weeks 5-6 surface looks dreadful on both the CFS and Euro so I will ignore them. Weeks 5-6 will change anyway. La Nina would lobby for a warm bal-winter starting around mid-January. However the -QBO helps keep blocking alive. Plus eastern Canada and Greenland heights are shown AN. 

Don Sutherland shares some useful statistics in NYC Metro's December 2017 Discussion and Observations thread. Sure it is very NYC focused. However he discusses the broad North American pattern as usual, so his posts are relevant nationwide.

[Carvers Gap]

The 12z GEFS is much more reasonable.   Versus sending San Fran into the Ice Age, it keeps the bulk of the cold east of the Rockies and then sends it East as Jeff mentions.

[AMZ8990]

1 minute ago, Carvers Gap said:

The 12z GEFS is much more reasonable.   Versus sending San Fran into the Ice Age, it keeps the bulk of the cold east of the Rockies and then sends it East as Jeff mentions.

That's a lot better then what we were talking about before.  Im still holding out hope I can see some flakes around the 26/27.  Models seem to be slowing the system down though so we will see!

[nrgjeff]

12Z Euro ensemble is similar to the GFS above. Cold eventually moves east. FWIW the Canadian ensemble is on board too.

Forgot to mention MJO forecasts impact NWP. Models will sort out position and intensity.

Looking back at some previous La Nina -QBO years with (mixed) SER and Alaska signal around Christmas, the cold eventually dumps into the Southeast. Includes some meh Greenland charts. Being near the winter solstice helps the cause.

I was surprised looking back. Perhaps recent history jades. Reality is that a proper delivery pattern (blocking etc.) usually brings the cold. Bering Sea ridge center (vs Alaska) might justify the delay, but I think the cold is coming.

[Carvers Gap]

I agree w Jeff.  Regarding the d10-15, the 12z EPS looks reasonable, very similar to the GEFS.  Western areas of the forum are pretty cold.  The cold presses further southeast than its run at 0z as tnweathernut and other mentioned it might.  Should make for some interesting temperature gradients for a few days as the cold oozes eastward.  Also, will be interesting to see how much precip rides that boundary as one would think it would.   

[John1122]

As was pointed out, the big EPO ridge in winter 2014-2015 dominated the pattern and smashed the SE ridge every time there was a conflict. I do recall the models would show the SE ridge in the extended only to never have it become a reality. NAO didn't matter, AO didn't matter. The Pacific drove the pattern. I don't believe the strange deep sw trough directly underneath the EPO ridge nor do I buy the power house SE ridge. But you can see broad NA troughs are common for the eastern 2/3rd of the country.

 

This is the normal pattern when we have that. I'm pretty excited to see it forecast.

 

 

[John1122]

This is what the GEFS was showing 12 hours ago in response to the EPO ridge. Look familiar?

 

 

 

[tnweathernut]

50 minutes ago, John1122 said:

As was pointed out, the big EPO ridge in winter 2014-2015 dominated the pattern and smashed the SE ridge every time there was a conflict. I do recall the models would show the SE ridge in the extended only to never have it become a reality. NAO didn't matter, AO didn't matter. The Pacific drove the pattern. I don't believe the strange deep sw trough directly underneath the EPO ridge nor do I buy the power house SE ridge. But you can see broad NA troughs are common for the eastern 2/3rd of the country.

 

This is the normal pattern when we have that. I'm pretty excited to see it forecast.

 

 

Thanks, John.... I couldn't remember when, but thought it was in the last few years.  It really was kind of fun watching big SE ridges never materialize.  Hopefully this year will be similar.

[J.C.]

7 hours ago, tnweathernut said:

Thanks, John.... I couldn't remember when, but thought it was in the last few years.  It really was kind of fun watching big SE ridges never materialize.  Hopefully this year will be similar.

You could be right.  The 00z brings the artic boundary further east this time putting much of the Tennessee valley in a ZR situation.  It's obviously only speculation at this point, but definitely a move in the right direction.

[Carvers Gap]

Days 10-15 and moving forward in time on the models.....Not to provide false hope....but I would like where I am sitting if I lived in the western 1/3 of the forum area after the overnight run, specifically Memphis northward.  Pretty much any of the major models are stalling an Arctic front (almost Arctic) over some portion of the western forum area...sometimes further East.  Like I said earlier, be glad we are on this side of the Apps.  Precipitation will run along that boundary.  If we could get that boundary to flatten out a bit, it could be a nice forum wide event.  Again, this setup seems to have ice as part of the equation on the southern side of the cold.  The 0z GEFS snow mean for west TN increased to 2-3" overnight for that time frame. The 6z GFS (operational) is a great example.  Around h240, a 1040 high comes out of the Plains following a front w high precipitation. Happens twice.  Not saying that is the gospel.  But it would be snow on snow for the western half of the state....and an icy mess for the rest.

[AMZ8990]

1 hour ago, Carvers Gap said:

Days 10-15 and moving forward in time on the models.....Not to provide false hope....but I would like where I am sitting if I lived in the western 1/3 of the forum area after the overnight run, specifically Memphis northward.  Pretty much any of the major models are stalling an Arctic front (almost Arctic) over some portion of the western forum area...sometimes further East.  Like I said earlier, be glad we are on this side of the Apps.  Precipitation will run along that boundary.  If we could get that boundary to flatten out a bit, it could be a nice forum wide event.  Again, this setup seems to have ice as part of the equation on the southern side of the cold.  The 0z GEFS snow mean for west TN increased to 2-3" overnight for that time frame. The 6z GFS (operational) is a great example.  Around h240, a 1040 high comes out of the Plains following a front w high precipitation. Happens twice.  Not saying that is the gospel.  But it would be snow on snow for the western half of the state....and an icy mess for the rest.

I was looking at the ensembles this morning and was thinking the same thing.  I was thinking of an ice storm threat from what  saw too.  All the ensembles showed some sort of snow though so that was promising.  Overall it was a good run in my opinion,  I'm anxious to see the next run now.  I did like seeing those cold temps that flooded down into the Tennessee valley around Christmas!

[John1122]

I've often found that during ice storm/arctic front situations that the cold almost always is deeper and further east than modeled 24-48 hours before the storm. It's also much slower to retreat. I would usually add a few hours duration and at least 50 miles south and east to any arctic plunge/ice event. This one is so far out that there will be plenty of time to monitor those detail if it comes to it. 

[PowellVolz]

I’ll take 33 and rain over a ice storm on Christmas. That would be a terrible situation.


.

[Carvers Gap]

Those big highs modeled in the Plains(the Euro OP has a 1040 high in central Canada at the end of its run) are trouble if that front stalls or slows.  With the overnight trends to push cold more south and eastward(John, tnwxnut, and Jeff all mentioned this as a possibility) and the overall trend to move the cold slowly...have to think that boundary potentially becomes a conveyor belt for moisture up and over the cold.  I remember Memphis getting snow in the 70s.  Used to be some crazy temperature gradients....30-40 degrees between Memphis and Knoxville.  Then it would push eastward.  For the longest time as a kid, I used to think our cold came from Memphis, because it sort of did.  Definitely still a ways out there, but the ice threat over the upper South does concern me.

[tnweathernut]

Big cold highs, a big -EPO and the possibility of a muted SE ridge bring visions of ice storms into my head.  If overnight modeling is right, and it looks more reasonable to me than the last 24-48 hours of modeling, then I think someone in the mid-south will have a chance to track a winter event in the days around Christmas.  Let's just say it's not the predominant cold and dry look we have seen with this current setup. 

Enjoy the relative warmth next week, I am fairly bullish more fun and games are just around the corner.  The EPS is really bullish about precip in the deep and mid south in the 10-15.

You probably shouldn't get too excited though, I typically remain optimistic, and as such tend to get let down a LOT.  lol

[Coach B]

31 minutes ago, Carvers Gap said:

I remember Memphis getting snow in the 70s.  Used to be some crazy temperature gradients....30-40 degrees between Memphis and Knoxville.  Then it would push eastward.  For the longest time as a kid, I used to think our cold came from Memphis, because it sort of did.  Definitely still a ways out there, but the ice threat over the upper South does concern me.

This continued on into the mid 80s. I often remember as a kid growing up in the Nashville area that if it was snowing in Memphis it was without question on the way. Seems like during the snow drought of the last 25 years or so this has not been the case nearly as often. 

Looks like the next week is going to make for some quality model watching. The 06Z GEFS is a good example of this. There are some quality hits for our region, but probably even more misses with the frozen precip holding to our NW. 

[Carvers Gap]

December 25th looks a bit different than a few days ago on the 12z GFS.  Bermuda high concerns and  to the current run....will it even get above freezing? 

[Carvers Gap]

Wow at the 12z GFS.  From yesterday night's run to now.  That is how teleconnections should work.

[nrgjeff]

Honestly the 00/06Z GFS is probably more realistic. However I wish the 12Z would be right. Ends with a true +PNA. I infer deeper cold with a steeper frontal incline - snow not ice. Perhaps the truth will be in between, not ice and not a bomb, similar to what happened Friday.

Ignoring the CFS today. All ensemble products are colder than the CFS. Ensembles are right near normal verbatim, but that average includes warm members. The majority of ensemble members are at least slightly colder than normal. Will await Euro weeklies tomorrow. Otherwise we are getting inside the 11-15 day anyway.

Too early (for me) to speculate on precip. However I'm fairly confident the cold front will pass our entire forum area. Might get hung up in the Deep South, but the front should get through the entire Mid-South and our Tennessee Valley.

[John1122]

1 hour ago, Carvers Gap said:

Wow at the 12z GFS.  From yesterday night's run to now.  That is how teleconnections should work.

That's a lot closer to the look of a big -EPO but it throws in a little bit of good for every teleconnection by the end of the run.

[John1122]

The GEFS doesn't bring the -NAO but keeps us locked in the Pacific driven freezer, ala Jan into Early March 2015. It's a pattern that can really stagnate with brief breakdowns. That run on the GEFS has the region above normal for 3 of the next 16 days. 

The NAO can aid even further but it's not needed for Southern storms. The storm a few days ago snowed way south and east of here with a +NAO. The NAO was predominantly positive in Jan-Mar 2015 as well. It was also predominantly positive in the very snowy Jan-February 2016. Granted that year was very latitude driven, as basically border counties with Kentucky/VA and points north were hammered while areas south of there were slightly too warm for most storms. 

If given a choice between a -NAO and a cooperative Pacific I'll always take the cooperative Pacific.

[Carvers Gap]

...and then the 12z Euro.  Great example of the butterfly effect.  The trough in NA finds a way to interact with a smallish piece of energy in the eastern Pacific.  That piece of energy then becomes a gigantic cut-off low and sends BN temps west of the Rockies.  It basically replaced the ridges with troughs and trough with ridges over the lower 48 from d7-10.  I usually never toss a run and won't this one either...but I am tempted.   The overall NA pattern is the same...but the downstream lower 48 pattern is greatly disrupted by the cutoff that comes into Washington.

[Carvers Gap]

OTH...the blocking near Greenland my use that trough swinging through the Northwest to dump some wicked cold into the US.  Pay me now or pay me later type pattern...in a good way.