Carvers Gap

The 12z CMC is now showing a similar break(like the Euro yesterday) from continuity. The MJO is now almost universally in phase 7 in the medium to LR which is a cold signal west of the Apps (warm for January though). At 144 the CMC has a severe ice storm for western North Carolina. Interesting this is the timeframe which was showing up on modeling a few days ago and then went poof! Probably a one-off, but that CMC run is not warm. Details embedded within patterns are what matter. Beware when cracks start to show in modeling, especially with the MJO showing high amplitude into phase 7 on some modeling.

The cold snap of 17-18 isn't spoken about much as it produce very little snow and bitterly cold temps. It occurred at the end of December and went to mid-January. That was pretty much it for that winter if I remember correctly. Would not surprise me to see a similar event. If that cold spell had not straddled two months, it would have created a ridiculously cold anomaly for a month. That cold shot is hidden buried in monthly climatology by means which were warmer on the front and back end of that cold snap. That cold snap was preceded by very warm tempt, almost 15 degree departures during a few of the days prior. The rivers here in NE TN (which didn't have dams on them and warmer generator flows) froze almost solid. I remember seeing squirrels walking across creeks which were frozen solid but nearly clear ice due to lack of snow. The squirrel looked as curious as me when it walked out there. This reminds me a lot of that winter. If we had any precip at all, would have been more memorable than it was.

Good post. Will be interesting to see if the MJO sorts itself out during the next couple of days. WxBell has had some good articles about it - D'Aleo's, as I mentioned yesterday, discussion was stellar. The SSW potential is there, meaning sudden warming is modeled in the stratosphere. I think the warmth Dec 10-20th is legit. I think the anomalies will be warm enough to make December as they will override and BN days. After Christmas, all bets are off. Lots of conflicting signals out there. And yes, as we previously spoke in this thread, ridges that connect into high latitudes from low latitudes are often like bringing a jack hammer into a China shop regarding what happens after that. My guess would be that cold is going going to press into the western forum area after the 20th. Will go back and look at trends in a bit. CFSv2 is definitely interesting. Could just be a blip and/or the model just a wicked cold bias...Modeling the next few days will be interesting to watch.

To clarify.....that November turned out super cold!!! LOL. Models were locked on warm. Looked like a slam dunk, and bam! They reversed course. May very well have been a La Niña year. Happy first day of met winter, everyone!

As the phrase goes, time will tell.

Normally, I would toss the Euro. I remember years ago that I was trying to convince John that November was going to be warm. Every model had it, especially the Euro...until it cracked in one run. So, I have learned my lesson. I tend to question modeling which doesn’t show at least some variation. That November Euro would then waffle around for a few days, until it finally flipped. The CPC MJO data is trending to 7 with some 8 showing in the individual ensembles. D’Aleo had a great article today on the MJO. Basically said the BN SSTs in the 7, 8, and 1 regions (La Nina) are not allowing waves to propagate into colder regions. Said this is why models are sending the MJO into 7 and stalling or circling back to 6. So the big question is does it stall in phase 7 or loop back to 6? It may well be that we see some loops from 6-7 and back in a wash-rinse-repeat cycle. If so, the pattern will be more transient than models have depicted. I am super suspicious of the wall-to-wall warmer look. Runs against a big cluster of climatology. So, we will see if the Euro is a one-off. Should see it bounce around some of it is legit. It would take very little to move the needle towards cold. The -QBO is a surprise this winter and will have to be dealt with at some point. We usually get our share of winter here at some point.

Sitting the school car line, but just wanted to state that the 12z Euro is quite the break from continuity from d5-10.

Hoping we see some of that rain. We are far, far from flooding problems IMBY. The Euro Weeklies from Monday were bleak in that regard. Hopefully as La Nina improves during the next 4-6 months, that will get better. If we get under the return flow from the Bermuda High(meant as a joke...kind of), maybe we can get some rain.

November finished -3.1 for the month. That is a stout departure from normal. Can't tell what the rainfall departure(very dry) is at the moment, but it is likely significant.

NE TN and the Plateau have a tad more wiggle room(different formula) than most in the forum area. The mountains here have already received snow - without blocking or a favorable MJO if I remember correctly. Still, we have some winters which were goose eggs. I think we get our chances. Nobody knows at this point.

And while we are on the topic of the MJO, there is still not a definitive trend on its loop into phase 7. In general, looks like it takes a turn into phase 7. Whether it loops back into 6 is a question. Whether it loops into 7, back into 6, and back into 7(hence a loop) is a question. However, I would not rule out a high amplitude turn into a colder phase 7 later in December.

Agree we are very likely in for some prolonged, very warm December weather after the 10th. However, the GFS has pretty substantial warming at 10mb and has consistently shown this for several days. Whether it can split the SPV, now that is another question entirely. I see a temporary displacement into separate regions before coming back together. However, by my definition, that is an SSW(sudden stratospheric warming event for new folks) - I did check the definition before posting this. Last winter we saw several times where the strat warmed, and it looked like it would knock the TPV off its game and did not. Finally, we saw a massive discharge of cold directly south into the nation's mid-section later in winter. I actually consider it a good thing for the SPV to get disrupted early. Now, glass half empty, one could say there is an SSW but the actually TPV is pretty tightly wound. I think we are seeing the top of the polar vortex disrupted, but it is not propagating down to the surface at this point.

And I should add, that if I saw modeling wall-to-wall cold, I would not trust it. Same rule applies for modeling today. A few years back, we had an SSW event during early February. Majority of spring predictions were quite warm. Pretty sure we didn't actually feel spring temps until mid April that year as winter was essentially felt during much of March. Again and not to beat a dead horse, most of the non-winters in E TN are a result of strong El Ninos and a few strong La Ninas thrown in for good measure. The coldest temps I have seen occurred during weak La Ninas and often had very little lead time in terms of forecasting. Always kind of a bummer to see warm temps prognosticated during the run-up to Christmas, but until the last few years(where we have had early season snows), December was a "no go" IMBY for snow. So, not overly concerned at this point with mild December temps. I don't think the base winter pattern is even close to showing itself yet. My non-winter comment originates from the idea that a warm-start to La Nina sometimes foreshadows warm winters, but if one looks at John's data above, there is a cluster of years where the cold didn't arrive until mid-winter or later. It is worth repeating that each year is its own analog.

My ideas during June had a seasonal to BN month of December with January and February being AN w/ BN snowfall(but more than last year). I think all bets are off right now. I "think" I remember correctly that during a handful of weak Nina winters that the overall pattern was not MJO driven. The MJO has been a huge driver of late, and I expect that to continue. However, I don't have all of my eggs in that basket. Second year, weak La Nina's generally have strong climatology which supports strong to severe cold shots even if the overall pattern for the winter is base warm. That was my thinking in June and still is now. The cold shot may not fit perfectly in the month of December. Models this morning are pretty warm for most of the Lower 48 not name Washington state -very zonal. Long way to go as meteorological winter doesn't even start until tomorrow. We have 14 weeks IMBY until things generally break for spring. I am sure lots of unpredictability and volatility awaits. As with any winter, surprises are a near certainty.

After Dec 10th, looks like some warm weather(above to much above is the question at the moment) is highly likely. Models have been persistent with this look. The Weeklies are SER in perpetuity(relentless on that run). I think my idea of an early start to winter (which I put out in maybe June) is headed for bust city. I think January and February have a good chance at verifying. That said, Jan may have a chance at seasonal if the cold is delayed. Although unlikely, I do think a non-winter is possible if the front end of winter is warm. Weak Ninas tend to deliver cold which models are generally blind to at range. So, I think we see 1-2 severe cold shots. Right now the MJO and high latitude blocking are a problem - bad Atlantic and bad Pacific set-ups. The strat warm is a MAJOR wild card. If the SSW occurs from Dec10-15, we could see the first incoming shots of cold into the lower 48 about 20 days or so after that....Cosgrove has a good timeline with that which is sometime after Christmas to the first week of January. So, the Weeklies are likely missing that shot of cold. However, if the SSW doesn't verify, we may be in for a long stretch of warm weather. That is surprising to me, but welcome to modeling chaos - it ain't always predictable. LOL. Huge grains of salt. Volatile pattern, but models seem to be leaning warm during the past 48 hours. Big ridge possible between the 10-20th of December. Would not surprise me to see us in the upper 60s and into the 70s IMBY.

LOL. Let's hope that run of the Euro Weeklies is not correct.

That is gonna leave a mark. What to really watch for is if a SER connect with the WAR, and consequently sends a ton of warm surface air from the subtropics into the TPV. That has been the sign of a top to bottom split. The EPS has been close as has the GEPS. Cosgrove correctly points out that most splits result in the cold heading to Eurasia. However, just seems like modeling likes having cold on this side of the hemisphere in the LR. I can say this though, modeling is going to be a total mess. A strat split can actually trump a poor MJO phase. I do not think modeling is even close to sorting out the LR outside of the SSW which seems probable.

I haven’t looked at them today...However modeling does show a few shots of cold consistent with phase 7. Then, MJO site shows a cluster of models which try to loop the MJO back into 6 which is consistent with the warm-up late in the LR. So, model output seems to be consistent with that uncertainty as they bounce around. Interestingly, the warmth seems to be getting pushed back some. I still like the 10-20th for a ridge to roll through/form in the East.

Not uncommon during second year La Nina's I don't think. JB has been calling for a strat warm forever. He has to be right at some point? I have noticed when SSWs begin to appear, modeling goes absolutely haywire. Was my first thought when I saw modeling go warm, then cold, and now warm again. I don't think they are done bouncing around. I think at some point, if real, we will see a high latitude blocking signal appear on LR modeling. Past few years, the West has won the SSW lottery. Climo might favor the eastern part of NA if the split pushes cold onto our side of the hemisphere. That is another reason we want an early split. Wavelength pattern favors us early.

Yep, indeed the 12z GFS nearly or completely severs the SPV late in the run at 10, 30, and 50 mb. Now, normally I give it little credence at that range, BUT it has an uncanny ability to nail those events at range even if it misses nearly everything else. Huge implications down the road if that early season split occurs.

With that big high, is the GFS beginning to sense an SSW?

There is a 1065 hp in the Canadian Rockies around 324 on the 12z GFS run. Fantasy land for sure, but I generally have found that when the GFS starts to "sense" those big highs, it is a hint that cold may well press eastward after first pooling in the Rockies. Definitely some uncertainty with the MJO as modeling can't seem to decide whether to leave it in phase 7 or loop it back towards 6. But wow, some gigantic highs on the 12z GFS.

Bit of a suppressed storm track on the 12z suite of models.

The 12z operationals for the Euro, GFS, and CMC all show potential in the d8-10 range. This is an amplification that was missed by the GEFS if I remember correctly. Now obviously, at this range no model run is right or wrong. The 12z Euro has a 1-2 punch late in its run. Way out there, but something to consider.

May be worth beginning to consider Dec 5-10 as a potential window for the first accumulating snows for someone in the forum area.