Carvers Gap

With the potential or much colder temps this month, and a tendency not to soar way AN....we could be looking at a top 10 cold month for TRI. I'll have to go check and see...but that is off the top of my head. 7 day ensembles for mid month are -10 to 15F BN

I am just now catching up on overnight and afternoon modeling, so please forgive me if I am on stepping in old footprints. These are the real feel temps for the mid-month cold front. The GFS I "think" had this on d16 of its run a few days ago. It is now well within d10. The 12z EPS is the colder of all the ensembles, and that gets my attention w/ its usual warm bias. Some deterministic models don't get us above 20 degrees. This reminds me of the 09-10 setup. It got cold right as school let out - as in the very day school was dismissed for Christmas. Cars were stranded in a pretty good commuter snow storm. This could be an 83-84 deal where it gets cold and doesn't snow. I fully see that. However, I see the Euro cranking a big storm high around this time frame. Often, we will see cold temps and big snows coupled. These temps are pretty much on bare ground. The GFS gets TRI below zero(in some places) with actual temps. The thing that concerns me a bit is that the GFS has the warmest MJO!!! If it is just now catching on(and it has a habit of seeing cold shots before other models at range during December), then look out. Still time for things to change, but a big shot of cold air is growing likely but not certain. Once we get to day 6-7, I think the cold is baked in the cake...so a few more runs to go. TRI has managed -6.8F and TYS -7F(for the first six days of the month) without strong amplification. What I am seeing w/ deterministic runs is a tendency to amplify the pattern sooner than later.

The other thing I am noticing is an uptick of the mean snow total over TRI. That might be "IMBY" a bit too much, but that is usually a good thing for everyone when it goes up. The 12z AIFS-Ensemble has 2-5" of snow from TYS to SW VA. The 12z GEFS has 1-6" of snow from TYS to TRI.

I just think climatology really doesn't support super cold air until mid-December. There are lots of "whys," but I also think the MJO wasn't in the phase where the cold centers in southeastern NA. But it is MUCH colder than models had it when the SER was once modeled here w/ highs in the 70s. IMHO, modeling has tended to have a shallower trough and that has verified. The bitterly cold air I have seen modeled has been w/ the cold air masses of Dec 8th and 14th. And to the number that matters, TRI is -6.8F for the month so far. That is pretty big departure. Every day has been BN w/ a trace of snow on two of the six days. I can say this...I have been freezing my tail off while running in the mornings. I pretty much ice skated one morning on freezing fog. Pretty good start in my book.

Apparently, I just need to miss the 12z suite for all **** to break loose. Shiver me timbers, GFS w/ a piece of the TPV! Storms on the Euro.

Agree. As noted by a poster in another forum(maybe ENSO on the main page), this is a pattern which is often hard to break down, i.e. cold over the Hudson Bay, a small ridge over the Southwest, and kind of a flat, stable trough in the East. That Alaska feed into the SE is a classic old-school pattern. I know we've talked about it before. It seems like modeling has shown this in the past only for it not to verify. This time it is in place. That is a cold, cold feed at times.

I kind of see this more as a system where NE TN folks(SW VA) see the snow hang on just a hair longer w/ NW flow to follow. It isn't a big NW flow event, but it is present on all short range models, especially for the Plateau.

This is probably a more favorable trend for our folks in North Carolina, but you can see the various iterations of precip backing.

I really thought there would be zero support for the 18z GFS solution w/ ensemble members, but there are a decent number which have similarity. There were almost none of those at 12z.

The 18z ICON hints at it w/ a second wave of precip. I would be really surprised to see it deepen this close to the event, but the dynamics are there. Just a timing thing I guess. All I can see as a difference is a weak area of lp forming along the coast. I am not sure if a lee side forms or an inverted trough forms. I am terrible at seeing inverted troughs.

The 18z GFS apparently popped a weak coastal and backed the flow. Definitely want to look at ensemble members regarding that. For a progressive model to form a weak coastal....that might be something to watch. It would normally be the first OTS.

You know, the 12z AIFS had a similar solution to the 18z GFS. I just didn't look that closely. It just wasn't as much snow, but still 1-3" of it.

They added 09-10 today.

Best I can tell is that we caught the same jet streak from the 12z run, but it backed flow just a bit. That is an extreme outlier, but interesting. Doubt it will be there in the future, but something to keep an eye on w/ low expectations.

Might have been a hiccup, but the 18z GFS lollipopped NE TN and SW VA for Sunday into Monday....as in half of a foot.

Someone remind me…the SOI tanking means a potential bigger winter storm, right? Strong amplification incoming and stormy.

I mentioned 95-96 yesterday. Interestingly, the d8-14 analogs have that analog(I didn't see it until today FTR). I am glad not to see 83-84 in that mix! Dec 2012 is double weighted as well. 19951129 20161209 20121128 20221129 19961223 20101212 19951204 20211222 20121203 20081231

Just looking at northern hemispheres modeling, the coldest air on the planet will likely be over the Yukon d8-15 roughly. The mechanism to deliver that into the Upper South is present in the forum of a flat western ridge. The colder of the air (for now) will slide across the upper MidWest and into the NE. HOWEVER, any kind of cutter or storm which gains latitude could send all of that into the Tenn Valley region. Both the 6z GFS and 12z Euro have minor slp events which do it. I cannot imagine what a big storm would wrap in. A portion of the TPV is basically parked over the Hudson Bay, and just pinwheels cold air southward. In other words, we have a trough modeled. The source region for that trough is very cold air. Remember these winters where NA was void of BN air...not this year!

The 12z GEFS has temps twenty-five degrees below normal in WI at 195 w/ all of that headed SE. During that same hour, our forum area has departures of fifteen degrees BN. That is frigid for an ensemble at this range. The 12z GEPS is even colder over our forum area w/ temps 20 degrees BN over much of the area. The GEPS brings another cold shot around the 21st. The 12z EPS is rolling. It has the same cold shot, and is a bit "warmer." It is only 10-15 degrees BN. That is cold for a model w/ a bit of a warm bias in d10-15. Short story, even at this range, there is a growing likelihood of very cold air making it to our latitude by mid-month. Both the GEPS and AIFS ensemble(to some extent), show the second cold shot around the 20th. With so much snowpack immediately to our north, these cold air masses are on greased skids.

The 12z Euro is frigid w/ a couple of days of real feels that have below zero readings. Both the 12z GEFS and GEPS ensembles show cold temps some time between Dec 14-17th. I suspect we see an anafront(a constant them of mine I know) at some point in that time frame. I think we could see 1-2 very cold air masses push through the area mid-month. And honestly, all of us would probably appreciate some moderation if those come to pass.

I think the next "system" will be Sunday night. The 12k NAM has it as does the RGEM. it is coming in at night. If the NAM is correct, that could be minor to moderate upslope for the Plateau and maybe the Apps. The MJO is a "choose your own adventure" this morning at CPC. It has yet to loop back around. But....the GFS and Euro now show it stalling in 8 - and I am still not sure that actually happens! If it actually stalls in 8 for a long period of time(and it is already halfway across 8), that would leave the door open for very cold temps. I almost kind of wonder if the CFS has it right. It trucks across the cold phases, rolls through the COD to 6, and then goes back through the cold phases again. That looks an awful lot like those CHI graphics Jax recently posted. Strong 1-2, strong Maritime, continues to dateline. I do think we have a cold shot coming mid month...we'll see if I am right! LOL.

The GFS has had this time frame(give our take a couple of days from Dec 17th) on-and-off as a potential time for very cold air. The 0z Euro also has this but just a bit shallower. The extreme solutions have not verified yet, but only IMHO because climatology really hasn't supported it yet. By mid-December, very cold air has precedent over the valley regions. This also fits recent MJO rotations - I have not looked a today's as of this post. Again, if you like nickel and dime events(sometimes w/ mixed precip), the next 2-3 weeks are full of them. Let's see if they verify. Right now the trough axis is slightly too far to the East. Where is the actual SER when you need it, right?

The 6z GFS might be its coldest run yet. The 0z Euro and CMC have several light events which are northern stream driven. Models continue to get colder.

You all are keeping the lights on which we appreciate greatly!!!!

I haven't talked a ton about the d10-15 today, but modeling is MUCH colder with it. The 18z GFS is frigid. Its ensemble isn't much warmer. The EPS at 12 was cold. I think the MJO juice has made it to the deterministic models and their accompanying ensembles @Daniel Boone! The juice is loose!