December 2018 Pattern And Forecast Discussion

[Holston_River_Rambler]

1 hour ago, Carvers Gap said:

I still look at each model run in amazement.

Euro is even stronger with the surface low than the NAM at 12z. 990mb in GA.  I plan on going up to Mt. Leconte, but that plan is based on the idea that snow levels won't drop below 4000 feet until maybe 3 PM or so. Don't think my little car can make it down Newfound Gap in more than 3 inches of snow.  Euro is also now introducing the idea of rain/ snow mix over areas like High Knob as soon as noon Friday. 

[Carvers Gap]

2 hours ago, Icy Hot said:

Hey Carvers, care to share the map you are referring to?

Assuming you mean the weekend system and not the Weeklies maps?  Bout out of attachment memory space...plus it is a rainmaker.  You can go to https://www.tropicaltidbits.com and just toggle the maps to see the storm.  It is pretty impressive.   Rain, but impressive. 

[Carvers Gap]

As for the 12z GEFS, that is close to where we want the 500 pattern to be.  Not there...but close.  The BN height over AK still are a problem as they don't teleconnect to cold along the EC.  That said, the retrograding AN heights near Greenland likely would teleconnect to a trough along the EC.  The 12z GEPS which sort of hit this pattern change to potential cold beginning during wks 2-3 has now lost the pattern which is not surprising given how far out the pattern potential is.

[Carvers Gap]

The 12z EPS is not the progression that we want to see and is conflict w the Weeklies last night.  Again not surprising...but before I believe that nice Weeklies run, I am going to have to see some LR ensembles give it some support.

[Holston_River_Rambler]

While we are waiting to see how everything plays out, I thought I'd try to dig around and find some images of the last SPV split and it's results, so we could use it to compare to what is projected to happen.  Again, I'm not trying to forecast any particular result. I don't think anyone can say one way or the other what or when the result will be, but maybe something to be learned as it unfolds by comparing it directly to what happened earlier this year:

Image/ animation 1: projection of the SPV split this past February:

Image 2, results of that split at 500 mb (taken from Todd Crawford on twitter): 

In some ways, as it's being modeled now, the upcoming one looks a little opposite? (not sure that's the right word here, but can't think of a better one) of the one from last Feb, in that the smaller vortex from the split takes aim at NA while the larger one stays in N. Eurasia. 

[Holston_River_Rambler]

One of the other things I'm interested in is the 3D structure maps some people are posting these days. The reason I think it matters is that the split isn't of a flat circulation, but almost like a big old tornado at the pole. The analogy is not quit accurate and not meant to freak anyone out, but it's the best image I can think of. Do parts of it split at different levels in the atmosphere? 

Example: 

 

As Ventrice states, it is just one model, and as in my above post, probably not exactly what happens in the end, but for the purpose of asking how it all works, see how the whole thing is deformed and the little vortexes seem to extend down not quite as far as the larger one. 

Here's an image from Masiello this AM that I think shows how this plays out through the entire troposphere: 

It looks at first like he is only talking about 500 mb, but if you look at the second map, you can see how that weakness extends up to the tropopause and how the SSW is impacting the highest levels more, tilting the overall vortex into almost one side of a triangle. 

Again not trying to say it will result in this or that, but if we can better understand how these things work, maybe it can start to take some of the uncertainty out of the equation.  Especially with how the effects trickle (or rush?) down to 500 mb, a level from which that is easier to see local impacts.

[Holston_River_Rambler]

Interestingly the Euro and EPS want the larger SPV from the projected split to end up more over the Davis Straits. Opposite of what the GFS is showing (larger SPV after split ends up over N. Eurasia) and the GEFS isn't even all in on a split. 

Not in any way trying to promote this person, but including the tweet because you can see both EPS and EURO in the link. (Saves me image space too) Images for future comparisons for how all this plays out. EPS/ Euro images are always hard to find. 

 

[Carvers Gap]

Just looking at the 12z GEFS trends in the LR (blues are trending towards lower heights...reds are trending towards higher heights).

[Carvers Gap]

Now, the strat split last year was the real deal...it just came about two weeks too late.  I had to pick up a water heater in snow squalls on what should have been a warm, spring day.  Climatology was working against us by the time it hit.  We had about six weeks of strong, high latitude blocking.  It is no magic bullet as is it likely has messed up some decent winters...but it has helped many to be quite severe in one hemisphere or another. Personally, I think the upcoming pattern will be good, with or without it.  I do think it will initiate strong blocking which could likely help us during what would be warm MJO phases later in January.  I will also add that the eastern half of the forum area probably benefits more from a Greenland block more so than say from the Plateau westward.  The block doesn't necessarily make things frigid(it could most certainly make it very cold), but it slows the jet and allows for more phasing opportunities along the coast.  It makes timing much easier.   Just as we saw with the recent system, a slp that taps the Atlantic is an eastern valley set-up.  Blocking allows for that.  Now, for the western 2/3 of the forum area...seems like you all need storms to cut over the eastern valley or up the spine of the Apps.  La Nina's might even be a better pattern for those areas.  You need a far eastern cutter basically OR you can depend on northwest flow stuff due to a PNA or EPO ridge.  Here in NE TN, a block over Greenland gives us the best of both worlds which is why we understandably like them....northwest flow and coastal genesis stuff.  Now, I am not "all-in" on the strat stuff right now.  Strat splits are like a bull in a China shop if they happen.  Sometimes, they are our friend and sometimes they are not.  But what they are...is really cool.  I suspect this winter they help, but that is simply a guess.

Still watching for the LR ensembles to support the Weeklies run from Monday night.  Every time I think we are getting to that great look...we lose it on the next run.  Overall, the EPS didn't look terrible at 12z.   Pumped a big western ridge as evidenced by 850 temps late in the run.

[Carvers Gap]

Basically, the strat split could give us blocking which will give us a nice storm track(provided it is not in New Orleans!) over the Upper South.  No guarantees, but it ups our chances potentially.

[Holston_River_Rambler]

Flash, I feel you in the Strat dept.

Each evening for me = "it's here, it's there, it's everywhere! when will it end??!!", but then I wake up the next morning and there's some new detail (Masiello, Butler, et al. posts), that makes me think about some new aspect. And then I'm like: I wasn't going to post today about it, but.....

then I do it anyway and second guess it for 12 hours.

 

As an aside, I do think hype on social media (and soon mainstream news I suspect) is going to get worse before it gets better.   By worse I mean more people/ irresponsible journalists (not saying all journalists are, but hype and controversy sells and gets clicks) will be using not even real time data, but modeled data at fairly long leads to make claims that the data wasn't really meant to support. Example: I was driving home from Kingsport today and my wife showed me an article on social media that was titled "Polar Vortex to make a Visit" or some such. I basically told her what I just said above and.......... I don't think that was the answer she was looking for. I don't know about y'all, but every time people I know who are not weather nerds/ weenies like me start talking about something like this, it seems to end badly in the sense that the hype dies a painful death. I don't want that for this one, but 'tis out of my control. 

For other folks reading this and thinking: "Well, where do you stand and what does this mean for me?" I really am, like I suspect anyone who knows enough about SSWEs to understand that so much is very uncertain, in a wait-and-see mode. We call it a sudden stratospheric warming, but the warming only helps induce what can benefit us. The warming itself does us no good. As I understand it, the main event is the reversal of winds aloft at high latitudes. In fact that is how SSWs are measured. Heat flux poleward is an indicator, but that heat is a an indicator for the trigger that slows the flow and causes the blocking down the road.   Energy waves heading poleward carrying relative heat from the equator break into the circulation of the SPV and if it is weakened enough, it shifts, or splits and breaks down.  The highest parts of the upper air flow slow and meander near the pole, while increasing and sharpening in lower latitudes. Maybe one way to visualize this is that it's like dipping a paddle into a river running one direction, and paddling it in the opposite direction??  If you've ever done that and watched the swirls and eddies, you know how chaotic it is.  Imagine that on a planetary scale! That's where the uncertainty lies. Even if it seems like the result is bad for us at first, it can change and vice versa.  I think Carver/ Flash's posts above pretty much summed up how I feel about it as of now. Cautiously optimistic? Optimistically cautious? Happy happy, joy joy? Murphy's Law? 

I wrote about a Rube-Goldberg machine earlier and I think the SSW (if a major one happens) will be like the last piece of the machine, the one that kicks it all off. Even without a SSW things are lining up, to paraphrase a poster from the MA forum, in a way people have been waiting for, well, years. The much-anticipated (and prognosticated by JB) Modoki El Nino, a Madden-Julien Oscillation that has thus far this fall favored the cooler phases, overall cool and wet pattern in fall (and not just wet, but record wet across the E and S !), low solar cycle, and probably other factors I can't think of right now. Yet it is the South, even if the upper/ mid South for some and in others at decent elevation. Murphy's Law gnaws at the back of my mind. Maybe it's just my superstitious side?  

Maybe this sums it up for me:

https://tenor.com/view/indiana-jones-drink-gif-10683045 

 

[Carvers Gap]

The 0z EPS, 0z GEPS, and 6z GEFS now have a clear transition to an eastern trough late in each run.  Some are more impressive than others.   The Canadian and American ensembles depict a very good look.  The EPS is almost there.  It has a developing trough in the East, but an east based -NAO and poor source regions for cold air.  As a matter of fact, seems like all three ensemble depictions will take about another week for the cold to drop into the trough...just a guess.  But anyway, very good looks on the overnight suites.  Looks like Jan 2-3 is when those three ensembles want the trough to take hold.  Again, that is the 500 pattern.  It will take the surface some time to reload the cold at this latitude.  As a word of caution, it is not uncommon for a new pattern to show-up on a model only to get pushed back a few days or even a week or two.  However, for now, I like the timing being shown.  It fits with when the teleconnections switch on the Monday Weeklies.  

[Carvers Gap]

Evidently the JAMSTEC is now cool(per JB) for weeks 3-4.  Euro Weeklies roll tonight.  I am definitely looking form consistency(compared to its last run which was good for those who like winter in the East) from about the second week of January forward.  BTW, Ben Noll has some good stuff on Twitter today regarding the pattern progression for January.  I saw a few of those Tweets posted in the MA.  I think he also has one w the JAMSTEC progression to colder.  Edit:  I will post this Tweet so I can save attachment space and it is just easier.  Here is the JMA..

 

 

[Carvers Gap]

Tonight's Weeklies supported the Monday night run....

Pattern begins to switch around week 3 w normal temps showing up that week.  Then it gets quite cold.  There are some dry weeks...but I think Jeff noted that sometimes snowy timeframes will show up w less precip.  The d32-46 time frame was MBN(much below normal) and precip was MAN(much above normal).  All of that is straight out of the El Nino climatology textbook.  Maybe we can get @nrgjeff to pop in and give some comments.  I will hold off on further comments so as to give him time to add his much appreciated input.

 

[nrgjeff]

Cold Pattern may achieve well in Jan. Supply issues noted with Ridge over Canada. However a PV split that favors NA would help it all work out. Sorry so brief. Here's what I've been up to recently.

https://www.tripadvisor.com/Attraction_Review-g1066443-d1946105-Reviews-Weather_Science_Museum-Chiyoda_Tokyo_Tokyo_Prefecture_Kanto.html

[Holston_River_Rambler]

At Carver's request here is the EPS weekly snowfall:

I feel like I have to say a caveat for anyone who might be lurking. This is the mean snowfall of 50 or 51 versions of the Euro run out 45 days.  There's reason to be excited because it at least shows a good chance that there is cold and a southern storm track. Numbers aren't as important in this as the overall pattern represented in the mean. Get the cold, get the storm track, and then roll the dice. 

Off to Mt. LeConte this AM.  Hopefully some pictures later. 

 

[Carvers Gap]

@nrgjeff, that is pretty much awesome.  Enjoy.

 

In other news, the GEFS flipped cold in the LR over night.  It isn't bitterly cold, but well BN.  

[Carvers Gap]

BTW, I like the snowfall maps because they can tend to give an idea of how cold and how much precip will fall.   Last night, the snow plot expanded over the East.  If I were to see it contract as it gets cold, then I have a tendency to think it will get very dry like it did late last December.  That was a good sign.  The amounts rarely verify for MBY, but the trend is what I watch.

[Holston_River_Rambler]

 I always feel like I'm going to jinx it though. Maybe this will offset it (just for my mind) Not that I believe the 3k NAM verbatim, but I may not make it home...

That is Kuchera by the way.

[PowellVolz]

BTW, I like the snowfall maps because they can tend to give an idea of how cold and how much precip will fall.   Last night, the snow plot expanded over the East.  If I were to see it contract as it gets cold, then I have a tendency to think it will get very dry like it did late last December.  That was a good sign.  The amounts rarely verify for MBY, but the trend is what I watch.

I do the same with the snow maps. I just look for movement in them until we get to 2 or 3 days out. It’s just a small tool in a large toolbox.


.

[Carvers Gap]

Not to be all sunshine and rainbows all of the time...I would like to point out that the 12z EPS was about as ugly as it gets.  Rolled the trough through around New Year's and then builds a monster NA ridge across 80% of the continent.  Only a sliver of eastern NA stays under a trough.  Shew, we want no part of that.  Good thing it is at range that the EPS has been all over the place.  Just wanted to mention that so folks don't think there are not counter points to potential cold, even within the same suite.

[Carvers Gap]

Hopefully that run does not gain support from later runs.  Again, the EPS has been swinging wildly during the d10-15 range and has been known to whiff on cold patterns at this range.  But we do need it to lock onto the cold at some point and move it forward in time.  That was a big shift from its recent progression.  Not fretting over it at this point as it has missed some major trough amplifications in the East during the past couple of months.  

[jaxjagman]

2 hours ago, Carvers Gap said:

Hopefully that run does not gain support from later runs.  Again, the EPS has been swinging wildly during the d10-15 range and has been known to whiff on cold patterns at this range.  But we do need it to lock onto the cold at some point and move it forward in time.  That was a big shift from its recent progression.  Not fretting over it at this point as it has missed some major trough amplifications in the East during the past couple of months.  

The MJO looks better today on the Euro,It's been trying to crash it into the COD lately into 4 &5.The last SSWE (split) last year happened when the MJO was into phase 5,seems very possible again.If the MJO can get stronger like the GEFS shows and even some of the Euro ensembles,it should get real cold towards the mid month,least that's my thinking.I've been concerned for our parts of cold and dry,i've been all in yalls parts,hoping we get some freakish storm for us this winter

[jaxjagman]

Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks 
NWS Climate Prediction Center College Park MD 
300PM EST Fri Dec 21 2018 

Week 3-4 Forecast Discussion Valid Sat Jan 05 2019-Fri Jan 18 2019 

The current Weeks 3-4 outlook is issued against a backdrop of multiple active modes of tropical and extratropical climate variability. The above-normal SSTs in the tropical Pacific are forecast to couple with enhanced rainfall near and west of the Date Line during this forecast period. To be sure, this is due in part to continued eastward propagation of a robust MJO signal, but nonetheless seems to represent the first opportunity this cold season of a low-frequency tropical-extratropical teleconnection pattern over North America. While there is some evidence of MJO influence in the extratropics over the past few weeks, the current suite of dynamical guidance is nearly unanimous in forecasting a high-amplitude wave train over the PNA (positive PNA pattern) region during Weeks 3-4. This is likely due to a superposition of subseasonal and interannual variability. 

In addition to the interesting tropical-extratropical connections over the Pacific, there is also the potential for a sudden stratospheric warming before the end of the December. While a lengthy discussion of the literature on this topic is beyond the scope of this discussion, it will suffice to say that the low-frequency negative NAO pattern forecast by the ECMWF during the 15-30 day period is at least consistent with any top-down influence of the stratosphere on tropospheric climate variability. 

The dynamical models (both operational and SubX) support a high-amplitude PNA pattern with limited arctic air available over North America. The dynamical models are thus quite mild over nearly all of North America as a result. The evolution of the MJO, however, would favor more high pressure at altitude over Alaska and far northwestern Canada than currently forecast by the dynamical models. The ECMWF, with a more zonally narrow ridge over western North America, seems to forecast a more reasonable temperature pattern with below-normal temperatures favored over more of the southeastern CONUS. The temperature forecast for Weeks 3-4 is constructed by starting with the objective blend of dynamical and statistical tools, and tweaking it colder over much of the eastern CONUS due to forecast NAO and MJO considerations. One exception is over the Florida Peninsula, where a very mild pattern in Week-2 and long-term trends preclude favoring below-normal temperatures for the time being. 

The precipitation forecast is neatly derived from the forecast circulation pattern. Two orographically defined dipoles are evident over Alaska and the Southeast CONUS, respectively. A southward-displaced storm track is inferred over the eastern CONUS, while anomalous southerly flow over Alaska favors above(below)-median precipitation over southern (central) Alaska. The preponderance of model guidance favors enhanced onshore flow over California during the forecast period, and so a modest tilt toward above-median precipitation is indicated. Below-median precipitation centered over Montana and extending into the Plains is consistent with mild anomalous westerly (down-sloping) flow. A fairly large areas of equal chances is forecast over the southwestern CONUS where statistical and dynamical tools are in poor agreement. 

While we do not issue explicit forecasts of winter weather potential at this lead, it would seem prudent to note that the forecast circulation pattern would favor an enhanced chance of winter storm events east of the Appalachians, including the major population centers of the Mid-Atlantic and Northeast, especially later in the period. 

[Carvers Gap]

1 hour ago, jaxjagman said:

The MJO looks better today on the Euro,It's been trying to crash it into the COD lately into 4 &5.The last SSWE (split) last year happened when the MJO was into phase 5,seems very possible again.If the MJO can get stronger like the GEFS shows and even some of the Euro ensembles,it should get real cold towards the mid month,least that's my thinking.I've been concerned for our parts of cold and dry,i've been all in yalls parts,hoping we get some freakish storm for us this winter

Great post, Jax.  Yeah, I am not saying I buy that run...just saying it is out there.  I think your reasoning is very good.  I agree.

[Carvers Gap]

The 0z EPS, 0z GEPS, and 6z GEFS now show the ridge over the East breaking down sometime around Dec 30/31 w a brief transitional window and then a trough establishing itself a few days later.   Temps will lag a bit due to source regions as Jeff noted.  The good thing is that most show some sort of retrograding area of AN heights working into the Davis Straits.  The GEFS shows it really well, and would be a great storm setup due to confluence over this area due to the Greenland block.  The EPS is a tad too eastward w its PNA ridge.  Now, we need that look to hold (during upcoming suites) and then advance forward in time.  If you haven't had a chance to read Jax's post on the MJO just above, it is an excellent write-up of the MJO and how it is influencing the pattern.  Overall, nice run overnight.  Transition at 500 looks set to begin around the new year.  The unknown variables right now are source regions which effects the speed and strength of any cold potential. 

[Carvers Gap]

Just took a look at the most recent GEFS and EPS runs...they look reasonably good.  The progression from above still looks on track at 500.  There are some not insignificant temperature differences between the two ensembles.  I say blend them, and should be about right.  

[Holston_River_Rambler]

Euro has been interested in New Years eve for a few days now, still is at 12z today. Might be worth keeping an eye on. Doesn't look like much cold air outside of extreme NE TN and SW VA, but maybe the rich get richer? 

https://imgur.com/a/jydwGw2 

 

 

[Carvers Gap]

12z EPS individuals have several that show a very cold intrusion of cold air just before the second week of Jan.  Now, obviously that is not rocket science as January is normally cold.  That is BN air at the coldest time of the year...whether it is right, IDK.  However, BN temps at the coldest time of the year is a pretty good shot at cold.  The opposite would be one would never want AN temps during August.  Why?  That is would be incredibly warm....mid to upper 90s stuff.

[Holston_River_Rambler]

12z EPS looking good at range for western areas for Jan 3 - 5.  500mb anomaly, MSLP, and 24 precip. show a storm coming out of the gulf in that time frame with western areas favored at this time. Fv3 shows an active pattern, but suppresses the storms. EPS shows a little more of a SE ridge, so more room to amplify. I'd say about 1/6th of the EPS members have a storm with snowfall in that general vicinity in that time frame.

FWIW the GFS/ GEFS family went wild with the MJO amplification into phase 5/ 6 today. Not sure whether or not that has a bearing on how it handles our weather, but a stark difference between Euro/EPS and GFS/GEFS today in how they handle the MJO over the next couple of weeks. Would be interesting if the amped GFS was right (IIRC it was last year in Feb.) Will also be interesting how that impacts overall pattern progression if such an amplified solution verified. As Jax pointed out if it can get stronger and stay amped in the cold phases, might be good down the road.