Carvers Gap

Not a lot of changes overnight. There is one trend which I don't like which is seeing the MJO loop into 8 and back into 7. The GEFS switched from being very cold at 0z to quite warm at 6z. Might be a blip and might not. Looks like American modeling, CFSv2 included, has had something change between 0z and 6z. Now, that is no uncommon but worth noting. GEPS and EPS look very good. However, I am wary of any blip on the GEFS in particular as it can grab a trend first. I do think the NAO does its work. Addendum: The GEFS at 6z weakens the -NAO more quickly. This is a bias in American modeling which is to break down high latitude blocking too quickly. I don't discount it though quite yet. Let's see what other modeling does.

JB mentioned this evening that some of the air being modeled is so cold that it is giving models fits. Remember last year how the models had the EC at record cold temps for a while, but it switched to the nation's mid-section. Models will be all over the place with very cold air. Key right now are the delivery systems are in place for Arctic air. Looks like cold will setup shop out West and push East. Classic, classic La Nina look. But everyone should have a health distrust of modeling at this range. Huge grains, right!!!

Another nice set of ensembles at 12z.

As Holston mentions, the 500 pattern after d10 has the NAO retrograde west and slightly south. Trend overnight(and yesterday) is for some modeling to connect that NAO to the Pac ridge. What we are seeing, and it is out here so huge grains, is a pattern which could potentially go BN right during the coldest weeks of winter. It is not impossible that a piece of the PV could get dislodged under that type of block and get sent into the Lower 48.

And the 0z. ICON looks similar, but is probably too quick with the transition....but that is a whopper of a NA trough at 500. 0z is less enthused, but if extrapolated....likely would have gotten there.

That is the first time in a while that we have seen the GFS break in continuity for that time frame. Really can't draw-up a better LR pattern than the 0z GFS. We have rarely had that look during the past 25 years. Both a -EPO and -NAO. Kind of doubt that verifies, but the NAO is doing its work there. Big change. Let's see if the model can hold onto that at least somewhat consistently for the next few days.

The 0z GFS looks great. It will surely change by the next run, but that is a perfectly placed -NAO and the model reflects that.

Reminds me A LOT of last winter....w/ the blocks in almost identical positions. Aleutian Ridge looks like it is going to be there for some time. As Jax noted a few pages ago, sometimes that ridge slides into the GOA...and that is optimal. Thing is that second year Nina's (off the top of my head) tend to center cold a bit more eastward. I noticed feedback in modeling in early December. I took 10-14 days for the feedback to eventually show something that didn't look like a "copy and paste" pattern. Pretty good look out there right now. Again, I think when modeling shows the "copy and paste" look in the LR, it is likely wrong. We don't need wall-to-wall cold for snow in January. Very interesting to see the CPC go w/ equal chances for pretty much the entire forum areas. Brave forecast in the face of a week of big warmth. They wouldn't put that out there if they didn't have pretty good reasoning. So, some good signs. Important to note that the Atlantic can drive our weather pattern here, doesn't always have to be the Pacific. Been a long time since we have seen back-to-back winters with strong -NAOs to work with. Though, I do think Pacific driven patterns are generally easier for computer wx models to work with.

Fantastic post. Click the header. That much of an anomalous west-based -NAO on a 10-15 day mean is just insane. We should start to see some chances around Christmas into the New Year with shortwaves rolling underneath the block (like the 12z GFS). It might warm up for a bit as the SE ridge pumps for a day or two in that timeframe, but that will be transient if it happens. Models often take a while to see the full effect of the block on the longwave pattern, and the EPS has generally done a horrible job from the start determining the strength of the block to begin with, so I'm not so sure I trust its depiction of the pattern over the CONUS as much as the other ensembles.

Boone right on time with those comments as both the 12z GEFS and GEPS both show what would be a sharply colder pattern just edging into view of LR models. Get some split flow into that pattern and that has potential.

Courtesy of WxBell. The Australian MJO plot....that is a good look.

These were published yesterday. Seasonal temps with normal precip in January....we take.

Just looking at both the 6z GEFS and 0z GEPS, I think it is reasonable to begin to start looking at a cold shot beginning somewhere during the first two weeks of January which given climatology is not surprising. Those are normally cold weeks. It would appear that Dec20-30th will be a transition time. IMHO, we are looking at roughly a 1-2 weeks of seasonal cold to potentially BN in early January. If we see BN temps showing up in early January, that is cold indeed as that is climatologically one of our coldest weeks of the year. The flip of that is that we don't want to see AN temps in early to mid August, because those temps are really warm. Again, once we see the MJO settle back down and the NAO establish itself, I suspect we see modeling trend colder. An aside, I consider a good thing to see the NAO for a second year straight during winter. -NAOs tend to cluster in groups of winters. Maybe we are at the beginning of a cycle where the NAO becomes a dominant feature during winter after a prolonged absence.

The 6z GEFS is a classic -NAO look. Will be interesting to see how that plays. I have seen some talk that NAOs are not a lock for cold. Noted and agree. However, what will happen is likely a suppressed storm track. I still think modeling is just now settling back down after the MJO snafu. Again, I also thing modeling takes a while to adjust to blocking. The trend on the GEFS this morning might be evidence that modeling is now starting to work through those things. The GEPS is nearly perfect. Let's see if the GEFS trends that way.

Love the posts @Mr. Kevin. Some of that makes my head spin, but good stuff!!! 18z GEFS is a great pattern evolution with the -NAO placed perfectly. Would be seasonal cold with a suppressed storm track. That would work.

Feel free to share. Would enjoy reading them.

Models looks really good at 12z. GEPS ensemble looks perfect. -NAO is showing up. Models are sensing that feature now. Always seems like it takes a few days to reflect effects at the mid latitudes once the NAO shows up on modeling.

Amazing. And then models should settle in a bit....they were all over the place today.

-NAO and -EPO on modeling are right there with the MJO. I don't think the MJO is related to the -NAO. The HLB in the medium and LR is textbook weak La Nina. The MJO is not without its exceptions as well. Kind of an interesting aside, I am pretty sure NC gets a lot of snow in phase 3...maybe one of the guys over there can comment on that. It also seems like that cold can come even if the MJO is in warmer phases during La Ninas - that is the exception but no without precedent. Again, have to be careful no to lean too much on one indicator, but it is also true that it has been a strong indicator during recent winters. I would argue the -QBO has equal or stronger correlation to cold winters. In fact, if this winter does not have a sharp cold shot, you might be able to count on one hand the number of times that happened with a falling -QBO - very few examples of that. Very much agree on the looping aspect. And also maybe @PowellVolzsaid this on another forum, but warm winters don't mean no snow. Sometimes warm winters can have a bit more snow due the storm track not being suppressed.

Good info. Yeah looks east based to me which is why the SER will likely fight all winter. That little ridge in TX is also a product of that on ensembles I think. Yes, the MJO is likely going to crawl. Looks like models have finally corrected for the tropical systems. We should now get a consistent progression with some loops(note crawling) embedded in that progression. The one good thing is if this can get into phases 8-1-2, it could be there a while and during the middle of winter at that.

edit: Actually not so much a dual block as a perfectly positions EPO ridge which is very similar to 17-18.

So the 12z GFS is how it is done...with one tiny problem. The air that gets sent southward from the Arctic is somehow warm! LOL. Normally, when one sees dual blocking send cold off the pole it is bitterly cold and well BN. This is like sending air out of the sub-tropic southward(some hyperbole intended). VERY UNLIKELY that occurs, but the look at 500 we take at this range in spades.

The other thing that is beginning to be a fairly significant feature on LR modeling is a well-placed -NAO. Now wouldn't be something to see a -NAO get us through phase 7, and then the MJO rotate in 8, 1, and 2. I do think dual blocking is now likely. So, the delivery mechanism is there to send very cold air into the Lower 48. But that SER is going to fight for every inch. Remember last winter when the cold made it to the Plateau and stop - THAT kind of fight. Now, I would guess the cold gets at least to the Apps this time, but with the sever cold holding to my west. But there are still a ton of uncertainties out there right now. Those uncertainties are whether the MJO can get into phase 8, location of the NAO block(trend is west), location of the Alaskan block, and whether the jet kinks just enough to allow cold to tuck under a big EPO ridge. I think the -QBO and cold fall argue for winter to push eastward. So, just could be a winter with some really wild swings coming up.

Last winter would be my example. D'Aleo does a great job discussing those tracks as does Cosgrove. Typical Nina tracks would cut west of the Apps and have sliders as primary tracks w/ secondary track along the coast which cuts through the Piedmont. Normally, tracks are rotten for the Carolinas unless on likes ice... Now, western Carolina can score BIG during Ninas and our TN communities in the Foothills can get upslope snow. But primaries are to the Ohio Valley, sliders along the mid-South, and secondary would be inland runners. Really, there is a good reason why many of our most memorable seasons are weak La Ninas. But....not sure what we are seeing on modeling is that traditional golden egg set-up....yet.

Surprised there hasn't been more talk about overnight model runs. Ensembles look good as do the operationals for the most part. 6z GFS even has Christmas Eve mood flakes for the higher elevations. As Mr Kevin noted yesterday, EPS has shown some good trends regarding the EPS and the -NAO. Looks like that continued overnight. Euro control is very cold and really locks in cold after the 21st. The GEFS and GEPS have a progression that makes a lot of sense, and would put into place a very cold pattern by the New Year. Still some things to sort out, but overall nice set of model runs overnight.