Carvers Gap

The 6z AIFS Euro EPS is almost identical to the 6z Euro…looks like they may have fixed the algorithm for the ensemble at wxbell. General agreement right now between deterministic models and their ensembles and the AIFS ensemble. Either way, four days to go(five for some), this could change. Right now the 6z AIFS is an increasingly bonified cutter. The AIFS has change quite a bit overnight. The AI models handle hp over the top completely differently. Honestly, I don’t trust the AI models as they have each burned me this winter pretty badly…I will have to dig back through the Dec or Jan thread and find it. The AIFS Euro has been very warm d5-15 and badly so…but sometimes it swings very cold. I have found the Euro deterministic to be more dependable in my own experience as we have gotten deeper into winter. The AI models look over amped….but deterministic models seem to be inconsistently handling the Baja low. The AIFS models may or may not be mishandling hp over the GL area…deterministic models have been sometimes too aggressive with cold this winter. When looking at the model verification graph posted by Tellico last night….the AIFS was kind of mid. The best model was the AIFS Euro ensemble, then the EPS, and then the Euro. Now, admittedly maybe that was just for that moment in time. As for the AiGFS…it has been completely awful at all ranges. I give it no credence. The UKMET/AIFS is a formidable pair and cannot be discounted. As for now, neither is budging. I had fully expected the deterministic models and their ensembles to cave to the AI. They have not. In fact, they may have trended a hair south from 0z or only nudged a hair north.

AI models have almost a completely different alignment and evolution of hp over the top of this storm. Are they right? IDK. But deterministic modeling is almost uniformly placing more cold hp above or just to the NW of the system whereas the AI models quickly dissipate the hp over and behind the system. Are they right? IDK that either! The 12z Euro jogged south of its 18z run, and is a tick north of its 12z run. Pretty decent agreement w/ the three deterministic models. It is not surprising to see models jog north a bit. However, there remains a risk of suppression w/ this and even at the last minute if those big highs verify to the north and northwest of the storm and can persist longer than AI models depict. Important aspects still to be ironed out, but we are getting closer to a solution - maybe. As of now, we are potentially tracking a strong winter storm which could impact portions of the forum area. Nothing written in stone at this time, but we will see where this goes.

ICON, GFS, CMC vs AIGFS, UKMET...so far

Choose your own adventure at 0z. Welcome to the show!

At this point, I think we take a bit of a suppressed system at this point. Once those systems jog north of us on modeling, they are tough to get back south. I suspect those big highs will either verify too big OR they will produce a storm along the front, and significant at that. I definitely didn't expect a southward jog at 0z. Let's see where other modeling goes. Pretty huge run by the GEM.....

at 132...full blown winter storm on the GEM and similar to the GEFS. I think suppression w/ that big high is the concern so far. I can't decide what to be worried about...haha.

At 114, the GEM has a 1055 high over the top of the system.

Oh, wait......

0z GFS.....is trying hard.

I want my power, Jeff. LOL. I can't watch Tenn lose heartbreaking basketball games without it!

Slider w/ no warm nose. Need that storm a little to our south - I think.

0z Icon is on board!

No idea, but fun question about if/how their is a connection. Just spitballing, I would probably say the tendency for amplification is partially QBO related. When you dig back through years with strong amplifications during winters, the QBO is often negative during the heart of winter. As one poster noted in this thread, some big snows in Juneau and Russia.

Of note, the 18z EPS and EPS AIFS are super similar. The AI is a tick north, but not by much. I can't say I like the trend for E TN at 18z, but we have a ways to go before that gets nailed down. A big trend north or warm nose tomorrow, and I will politely hand this off to the middle and west guys(same for most recent Nina winters!).....again, probably need 3-4 more runs to really get a good handle on where that nose sets up shop. All great storms have the warm nose....need that high to build in. HOWEVER, I do worry a little about suppression w/ the 18z GEFS and EPS losing moisture transport northward....so let's worry about it all. Haha.

For sure, hopefully we will have a clearer picture by tomorrow evening. We battle the warm nose w/ nearly every big system over here. Will reset and head to 0z.

So w/ the AIFS EPS out of commission on WxBell...here are the 18z(left) and 12z(right) comparison of the EPS and GEFS runs. I prefer the EPS right now as it has been steady. Let's hope their algorithms are right! The 18z GEFS trended south. The EPS might by 20 miles north and a bit drier as well on the northern fringes.

Haha. Definitely a bias or algorithm issue there!

Eyes -> 18z GEFS and 18z AIFS EPS snow means for the entire run.

Better than tracking SLPs in the Lakes!!!

I am gonna ride w/ ensembles for about 24-36 more hours, and watch deterministic runs for trends. I don't use the AIGFS stuff. I barely use the GFS. Overall trends: 18z Euro(only to 144): trend north w/ ice over much of the forum, but...sure looks like the second wave would be snow. 18z EPS(only to 144): Looks super steady...maybe a tick north. Looks ready to deliver the goods. Looks remarkably similar to the AIFS Euro. I trended a hair colder. 18z AIFS: Slight trend north, and northernmost of all guidance. Looks a little overly aggressive w/ the warm nose, but that has precedent for sure. 18z AIFS EPS: Slight trend north but the accumulation map has barely changed at all. Temps barely budged. Steady. 18z GFS: Slight trend north, and southernmost of all guidance 18z GEFS: Accumulations are much higher than previous runs Things to watch....we need a true banana high over the top without a hp slipping eastward too quickly. I highly doubt models have this nailed at this range. IF(huge IF) the GFS is half right, then the followup waves will almost certainly be frozen for E TN. It does look like a multi day event. E TN for sure will have to watch the precip axis. I can just about guaranteed modeling will continue w/ its ebb and flow. NW TN looks favorable w/ this setup as it normally does. Middle looks good. E TN north of I40 probably is ice to snow. Crapshoot south of that...and maybe a crapshoot in NE TN. FWIW, one of those 93-94 or 95-96 events(maybe both!!!) started out as freezing rain during an over-running event and switched to snow. I think we see that setup. TBD on rain/snow/ice lines. I may try to do the late night suite tonight, but my tradition is to look at those in the AM along w/ 6z and then post at 12z.

I like the 18z Euro(non AI) and 18z Euro AIFS EPS. The look almost identical. Ice to snow over NE TN. May even start as some light run. The AIFS EPS pushes the cold front in quickly as soon as precip starts. That cold air just crashes into the system.

The AIFS has never really been snow for the eastern valley, but its ensemble has. I haven't looked at the 18z ensemble yet. The actual operational Euro look about right IMHO.

The BIG difference is how the AI models are handling hp. They are quicker to move it east which allows precip to nose northward. The deterministic runs hold much more hp behind the system. I will have to look at trends to see if one set is moving to another.

The 18z Euro(non AI) makes a lot of sense.

And that AIFS ensemble was honking for a winter storm at 12z. Let's see what 18z does. Looks to me like AIFS Euro, then EPS, then Euro??? The AIFS (at that time) deterministic looks a bit down there, but I can't really tell. I agree w/ the top 3 if so. Though the AIFS EPS is a bit to snowy as a bias.