Carvers Gap

These are the changes for week 3 of December. Ridge is out of the Aleutians. There is no ridge bellying into the SE. This would allow for northern stream systems and sliders. The control is MUCH colder than this.

Comparing week 2 of December. This is the change which is seen on the Euro Weeklies. This was derived from the 0z run. The 12z derivation would have certainly been even better. Notice the SER is gone. Notice the EPO ridge? It isn't in the Aleutians which teleconnects to AN heights over the SE. That is a 1,000mi change in the Eastern Pac ridge. There are AN heights over Greenland. Those changes IMHO are a direct result of things resolving w/ the erroneous(?) Baja low. The SER doesn't get pumped long term. addendum: Yesterday, the blues and yellows were exactly where u didn't want them. Today, they are generally where you want them

Noticeable shift colder today on most models with the exception of the CMC deterministic. The Euro Weeklies have returned to their cold look and serviceable 500 pattern for December. By the second week of December, they begin to push the cold for the rest of that month - equilibrium restored. The Weeklies, contrary to some comments on other forums, had a major change about two days ago. That first week of December has pretty much been warm on those Weeklies for some time. Nobody is upset about that. The thing that was frustrating to see was the Weeklies completely lost the rest of the month of December, especially after nearly 4-5 weeks of cold being shown. The Euro Weeklies have been anything but steady this past week - welcome to shoulder season. I really think the problem was feed back over the Southwest. Now that is being resolved with each passing run, modeling(deterministic and ensembles) is beginning to correlate again with the MJO and LR ext modeling.

The 12z Euro deterministic also kicks out the energy out of the Southwest. The EPS is a little slower to do so, but I am going to guess it does the same. Both the 12z GEFS and EPS have a formidable cold look now. The SER flexes are short lived. Just file this one away for later used. I would say 75% chance that what we saw yesterday was feedback across all modeling. It caused havoc downstream from that. I would suggest modeling in the d8-14 is still in the process of correcting.

The 12z Euro has correct as well. Storms are kicking out of the Southwest as one would expect. Now that modeling is getting that fixed, we should see some downstream corrections. I would expect for something to track pretty soon.

I think the multiple cutoffs to Baja and/or Southern Cal....was an error. The GFS has a bias to be progressive, but because of that it will work this out more quickly. The 12z gfs and ensemble matched the 6z run. The CMC is still coming around. In fact, the GFS is flirting with snow around Dec7-8. My guess is that cuts along the Ohio River Valley. But things don't hang up...that cold front will come roaring through at the end of the first week of December.

Overnight, it looks like the GFS started to get rid of the feedback over the SW. The 6z run pretty much eliminates it after the 6th. There will be a cutoff out there, but the GFS(and its ensemble) kick out everything after it. Is this because the model has a progressive bias? Maybe. But it would also be the first to fix whatever is going on(if indeed there is a feedback error which seems to be growing more likely).

Hour 276....we have some things to get worked out. The difference in the Euro AIFS and GFS ta 18z over Nashville is 58 degrees. The Real Feel on the AIFS is 3. The GFS is 61. The AIFS did not dig into the SW w/ the SLP FWIW, but it did the second. That still allowed a massive cold front to crash eastward on Dec 3 on the AIFS. The AIFS even dropped 1-3" of snow north of I-40 from Nashville eastward.

Option 1(and there will sure be options 3,4, and 5!) is that the trailer vortex spins out to sea. That is the 18z version. Option 2 is what happened at 12z. The trailing vortex followed and dug out a huge trough which allows a third vortex to drop into. We need that first vortex (even if it goes to the FC...to dig less and kick earlier). I think the first vortex digging into the SW is legit. I am not sure I buy the second and third vortices doing the same - that smacks of feedback. If the second and third vortex simply "don't go to Baja" then the trough likely digs into the EC. Take a minute and looks at the little vortices which modeling is juggling. There are four rotating around the EPO ridge - not counting the Four Corners low. This set-up is an absolute thorn to work out. The downstream effects are huge. It will be interesting to see how this works itself out. OK, enough stream of though posting. It is Friday night, and I am chilling. Will check back later.

Night and day differences when the SW doesn't have multiple lows cutting off...I don't know which is right. But the 18z GFS gives me some hope that the multitude of cutoffs in the SW may well be a feedback error.

The second vortex (which follows the Four Corners low) is the problem. During the 18z run it literally cuts directly through the ridge in the GOA. At 12z, it cuts over the top and dives into Baja which deepens the western trough. You can see the variations on the panels of the ensembles. About half have a trough in the East and half have a ridge - thanks to that little vortex. The EPO ridge is so tall that it is rotating energy back under it which is causing westward flow of Cali. If that vortex doesn't sit over Cali, I do wonder if Santa Anna winds might develop as a result. edit: When the first Four Corners low doesn't dig as much, it doesn't really leave much room for the second to follow. All of this is something to watch on future runs. Until this gets worked out, everything from Weeklies to deterministic runs are going to be impact IMHO. Why? That series of cutoffs takes almost a week to resolve. In other words, there are 5-7 days of cutoffs if not more (on previous runs). If we are looking at just 24-48 hours of a single, cutoff low...that allows for the trough to form in the East. It is a great example of the butterfly effect. The difference between record highs at 12z and the PV heading south at 18z....look nor further than the SW sequence.

Look at the different in the eastern half of the US. The first low(now in the Plains) is shallow and digs less. The second vortex spins off the Cali coast(westward). Not sure how much of that is believable, but this illustrates what happens when perpetual lows don't form in the SW.

Just watching the 18z GFS run, it is already very different over the Southwest. The second shortwave does not dig over the Southwest. That yields an entirely different outcome. That subtle change illustrates how important that sequence is....

Haha. I know I have lived this discussion before! This is why I love this site...we can look back at other winters. Also, google our forum for Baja cutoffs. Lots of great discussion for those.

If the Baja/Southwest cutoff is simply feedback, we should start to see the slp slowly creep eastward with each run, especially the first (in a series of 3!). If that is indeed feedback, you can bet the rest of the (previous runs) are probably not correct. Something to watch on this rainy, fall night.

The flip has been quick! The trend has not been our friend, but it is only November and we have just begun to fight...or something like that. The pivot away from BN heights over Tenn Valley has voluminous support both in width and depth in the model world. From ensembles to Weeklies....the trend is towards a standing wave SER over the SE. It can be beaten down, but it immediately returns. Outlier models such at the Euro AIFS and GEPS persist. I don't discount those. If cold is coming, the Canadian model will see it first. What we really want to see is the GFS deterministic to start bringing cold eastward OR the Euro control weeklies. That Weeklies Euro control is a nifty tool. With the exception of a few days earlier this week, it simply refused to be cold for December. The repeated troughs into the Southwest are an ominous look if you like snow and cold. I keep asking myself this question, "Have I been burned more by Baja lows which actually formed...OR have I been burned more by modeling which erroneously (due to feedback) put that feature in the Southwest?" I guess we will find out soon! Modeling often performs so poorly over that region. I find it pretty hard to believe that the MJO in phase 8 is going to end up being warm. So, I do think there will be some moderation(from AN heights) back towards seasonal and maybe even BN heights at some point for a 7-10 day period during December. The Euro Weeklies today are cold at the surface, but I now think that is a bad, bad bias(and a new one at that) and an error. Its 500 heights are now pretty much AN for most of December. That would imply cold will push some, but the SER is the base pattern. Again, this is shoulder season, and trends will likely still change - we can hope, right?! However, for me anyway, my hopes that models are delaying the cold diminish with each passing run. The reality is that it might not come to pass for much of December. But it only takes one memorable snowstorm to make folks forget a warm pattern! Besides, we usually don't get a lot of tracking in the valleys until January or Feb. We aren't even gonna talk about the retrograding BN heights(over the HB) into the West to start January! If LR ext modeling was wrong about December cold, it could certainly be wrong about a January pattern at range! I wish I had better news. I will give it a few more days, and then I will almost certainly have to adjust my winter ideas. Have a good weekend, everyone! At least we are getting some much needed rain.

Very short post. The Baja low looks legit. It is still possible that is feedback, but unlikely since both the 12z CMC and GFS both have it. After the Thanksgiving cold snap, a standing wave will result due to the Baja low. That BL will pump a ridge over the eastern 2/3 of the United States w/ a rare Bermuda high set in place to start December. Record highs are possible over some portions of the SE. It will take some time to break all of that down. Right now, the bigger concern is that ensembles continue to hold the cold pattern in the d10-15 range as does LR ext modeling. This could be a delay in the overall cold pattern or it could mean that modeling is just wrong. Something is gonna have to give though. The MJO is set to rotate into cold phases. Either the MJO forecast plots are wrong OR modeling is simply not recognizing the MJO plot quite yet. Remember, sometimes modeling will not "see" MJO influence in the d10-15. I would guess we will see a very strong cold from around December 10th (edit...NOT d10), and that unleashes the cold into Lower 48 (east of the Rockies). Interestingly, I do believe the Euro Weeklies have developed a cold bias. I don't know if they tweaked something, but it seems to be the default in the week 3-6 range???

The Euro Weeklies look like they have for the past 3-4 weeks which is cold weeks 3-6 w a warm up at the very end. They were prob a bit quick with the pattern change. They are about two weeks delayed from the original cold looks of a few weeks ago. For now, I think Dec 10 to just a few days after NYs looks BN for temps. For snow lovers, the concern would be cold and dry. The good thing about a +NAO is that the Gulf would likely be open for business. Could be warm up and rain…just have to time it with some of those inevitable highs coming from the prairies of MT. With a potential for SSW…we could see the cold hit 2-3 weeks after which would be an extension of cold into Jan. Model chaos on the horizon indeed.

IMHI, it really isn’t a Texas Blue Norther. That Euro cutoff partially pumps a ridge which locks all but the northern tier out of the cold during the first week of Dec. It is the Four Corners cutoff which drifts southwest into Baja and slowly runs out of steam…that is the pattern issue in my book. I am fine with a SW cutoff which eventually kicks out - pay me now or pay me later set up. The slow stall and drift into Baja is the thorn. The good thing is most ensembles get to the same EPO/PNA ridge setup by ~d14. The NAO(chuck mentions this in the MA) has gone poof, and that doesn’t push BN heights(over Canada) as far south as originally prognosticated. The Weeklies are only half completed as I type. I see Jeff has posted. Gonna hit enter and read it.

I mean really this is just a repeat of the start of our past La Nina winters for the past decade, including the model delay of cold air. What I am really interested in is this....With this shakeup on modeling, does it displace the entire pattern cycle by at least 7-10 days IMHO??? That may well leave us cold to start January - maybe.

There should be some wild model swings, but we are gonna have to let the dust settle after the past 24 hours of models flip flopping. They may go back cold like the AIFS. They may trend much warmer if that cutoff is a reality. So things to watch? Does that cutoff leave the SW or does it stall out? If it cuts of and stalls -> SER here. If it ejects -> big time cutter w/ cold following. Until that gets worked out, just guess work.

I had a ton of posts up this morning, but as I dug through modeling one thing was clear...ensembles and their deterministic runs were signaling a big warm-up after the Thanksgiving cold. How long does it last? IDK. In a rare move, I deleted all of those posts. Why? When modeling moves in unison towards warm...something is afoot and it usually isn't cold. The MJO argues for a very sharp cold trend in LR modeling which is not present yet. Sometimes, modeling doesn't "see" the MJO until about d10-12. The problem is the MJO really doesn't drive winter weather until Jan/Feb...and maybe late December. Right now, everything is very volatile after d10. Extreme cold is still on the table but kicked to December 8th or later IMHO. Outside of experienced mets, nobody knows what is coming w/ that cutoff low and SSW projected. An amplified pattern appears likely with wild swings between cold and warm.

Yeah, sure bet SSW is wrecking havoc on what looked like a good pattern without it. We have seen this many times during the past winters -> good pattern at range gets wrecked by an SSW. The only positive with an SSW is that it could put very cold air over the eastern US. My guess is that it dumps into western Canada and Montana and SLOWLY oozes west over a period of 1-2 weeks and modifies greatly. The big thorn in the medium to LR is a cutoff low over the SW which dives into Baja to start December. Until modeling works that out, the EC wx pattern is probably wrong. If that is real, that will pump a monster SER over the SE. There is ample precedence for this. Sometimes modeling is correct. Sometimes it is feedback. The 12z Euro goes absolutely bonkers with it. It creates a chinook over the southwest which pumps record heat into the souther half of the United States - like summer time heat for early December. I have looked at major ensembles today at 12z, and they are just wrecked. No other way to put it. What do I mean by that? Consistency is just shredded. In "general," the can has been kicked by a week at least. The Weeklies caught this first. I may just start using the Weeklies...LOL. However, the MJO and ensembles definitely foretell of a huge trough over eastern Canada by d14-16. Problem? The SER is flexed big time, and that standing wave is gonna have to get knocked down w/ several cold fronts. It cuts the bottom out of the trough. Seasonable cold looks like the outcome if today's iteration is correct, and it probably isn't. Let's hope the EURO AIFS and GEPS are correct, and they could be. For now, I am kind of watching the timeframe just after Thanksgiving. I wouldn't be surprised to see a NW flow event or storm pop w/ that. 500 vort maps are not missing by much when it comes to both streams. Overall, I think the cold is coming, but any time models start "can kicking" in unison, be very careful about expectations. I wouldn't be surprised to see a record cold outbreak. I wouldn't be surprised to see it completely vanish at our latitude. My gut says extreme cold is coming for the Mountain West. Why do I think this? 15 years of watching it do that 90% of the time. It will make its way here probably between Dec 10-25. Then we warm up. I suspect the cold reloads quickly and we see another bout to start the new year. While I am bearish now for early December, I still think we see a reloading cold pattern which is prob the result of the SSW. But for now, I am "out" on early December extremed cold. I think it will be seasonable to AN for week one, transition week 2, and maybe a cold week 3 before warming back up...and reload.

What is even wilder, a lot of higher elevation folks are already on the board. I am even on the board w/ 0.5" of snow already, and w/ a NW flow event to boot!

The mean doesn't have dump into Texas. In fact, it might have the trough too far to the East. Right now(and I know you know this...but this is for new folks), it is so tough to know the trough axis at this range - IDK at this point. Some modeling is just sending the cold straight to Texas. Some tends to send into the SE or NE and the MA. I would suggest the MJO is driving that along w/ the SSW. If that MJO stalls, we all will probably be just wanting it to warm-up. In my mind, I see a cold shot after Thanksgiving, a warm-up, another cold shot around the 3rd which means business....and the cold keeps on coming until about Christmas when the pattern moderates. The danger is that some modeling does not want to moderate after Christmas. There is a small camp of model runs which deepens the cold to enter January. In fact, seasonal cold is the warmest those runs get w/ well BN being the base pattern. Now, I hate even to mention that on a forum. If it doesn't happen, the disappointment is tough for some....and that hasn't happened since maybe 09-10 But it is worth noting. Those runs aren't quite outliers either. The MJO above would support some of those runs. The interesting thing is if the MJO were to loop back into the cold phases w/ no tour through the warm phases...we haven't seen that type of plot recently. Plus, there is the rare tour-de-warm MJO that never gets warm. This is IMHO is class -QBO territory in terms of analogs.