Carvers Gap

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.