Carvers Gap

So the 23rd system is now acting like a clipper? (Referencing the comment above). I actually agree with that if so.

The system on the 23rd (in the Midwest and eastern Plains) is a shell of its former modeling self. I am not sure I classify that as a cutter as no energy really cuts. That is a northern stream system which means the problem we fight is that it goes to shallow as at the even nears. This systems has gone from Miller A to hybrid to blizzard cutter to as John notes...almost a clipper (if I am reading that correctly as we are talking two storms now in this thread). As for the second system...not sure. The GFS and CMC handle in a completely different manner...one is a clipper and one is a Miller A. For the sake of clarity, I probably will move future comments about the "maybe" system on the 27th back to the pattern discussion thread. If it becomes anything, might worth a thread of its own.

One thing I am noticing is that the actual cutter is barely a cutter. I could be wrong(wouldn't be the first or last times), but it looks like a northern system w/ a cold front. The snow amounts in the Mid-west and eastern Plains have diminished remarkably. Not sure that changes the overall solution, but that is looking like an error(too strong) by all global models.

While modeling has struggled w slo placement, they have been incredibly accurate from d10+ re: temps.

It is important to remember that wx models are tools much in the same way carpenter’s use tools such as hammers or squares or levels. Whether they are used accurately is up to us. On to the ex...The 6z Gfs isn’t budging and is a true anafront where - the precip is behind the front. While I don’t trust that model, the Euri struggled with this setup a couple of years ago if I remember correctly. I don’t trust it either. think part of the issue is tracking storms from ten days out. There are 40 different runs(one just one operational model) but ultimately one verified reality. I think a blend of modeling is not a terrible idea at this point.

The CMC has been verifying higher than the GFS and Euro at d10+. Several times it has had a correlation coefficient of 0,8 or more.

The CMC has a major winter storm in the 27th. Modeling is all over the place with that system. Something to watch,

This thing is coming like a freight train.

Both the CMC and GFS at 12z are picking up on northern stream energy around the 27th. The GFS solution is wild - dives the system through west TN all the way to the GOM and brings it back up the coast. The CMC has a slider. Something definitely worth watching.

For posterity. Departures from normal and not actual temps. 12z GFS...

Tagging onto @Stovepipe

I think it is reasonable to say that there is potential for some snow with this front. Could be flurries. Could be snow showers. Could be light to moderate snow. The CMC has it, but likes middle TN more. The one thing I noticed is the 12z sped up the second storm quite a bit, and the spacing between the first and second storms decreased by quite a bit. Upper middle/west TN continue to be in the consensus sweet spot w/ NE TN being a wild card - may depend on totally on upslope(not good for MBY but good for areas east of I81). I highly doubt modeling is anywhere close to nailing down ana front amounts if those do indeed occur. While I don't trust the GFS at all past d7, it seems a bit more adaptable than other modeling w/ stronger storms in close range. Good test upcoming. I would not be surprised to see it score a coup, though amounts were slightly lower this go around.

Pretty significant upslope signal for NE TN and SE KY. 2-3" fall after the initial front. Let's see if it has any support. This is basically the same set-up as 6z, just a little bit less juice. There are some changes to the overall storm. As this nears the coast, we could see one final switch-up in modeling, and that may account for the changes we just saw.

Just digging into the dreaded MJO, the GEFS looks like it is forecasting the MJO on a different planet compared to other models. That is likely why it is putting the trough out West d10+. It is trying to stay in the warm phases when virtually all other modeling rolls into the colder phases. Could it be right? Sure, but would be the first time in several months for it to be right at d10+.(really since the fall upgrade).

But...we are going to have to see it get some support. It is on an island with that run. So, all caveats apply when looking at clown maps of one outlier run. Let's hope it is the beginning of a trend. The run does make sense though.

Addendum...that map is heftier due to upslope which follows in the 24 hours after the front. Many areas north of I-40 pick up 1-2" more in the bitterly cold air that the precip falls into.

Yep, that looks like an ana front signature. You can also see where the elevation is in TN. NW flow develops the next day. WB must be more smooth than Pivotal.

I am assuming MRX probably wrote this prior to 6z...This will be remembered as one of the great pre-Christmas fronts. We normally don't see these in December, but it does remind me very much of a couple of years ago around this time. The models are coming into better agreement on the pattern for Thursday night and Friday, as the GFS has trended toward the ECMWF solution of a closed low developing over the MS Valley/OH Valley region on Thursday night, with the surface low rapidly deepening and tracking across the Great Lakes region. This solution keeps most of the wrap-around moisture to the north of our area, and the GFS has backed off on it snow amounts. Confidence is increasing that this won`t be a significant snow event. However, the blast of arctic air into the area will still have the potential to cause significant impacts. The GFS continues to be slower with the timing of the cold frontal passage, showing it occurring after 12Z Friday. But this timing is not as much of an outlier among the NBM members as it was with previous runs. So the forecast will slow down the arrival of cold air late Thursday night into Friday morning, mainly between 06Z and 12Z. With this very cold air moving in quickly, any moisture on roads from earlier rain will rapidly freeze. This will continue to be the focus of impact messaging for the holiday weekend. Through Friday, strong cold advection will result in high temps occurring in the morning, and falling through the day. Isolated to scattered snow showers can be expected all day, with the greatest coverage in the northern half under the upper low. Winds will be strong and gusty behind the front, likely 15-30 mph with gusts of 40- 50 mph. With temperatures in the teens and 20s on Friday, and single digits Friday night, wind chills will reach dangerously low levels, especially in the mountains.

I wouldn't begin to know the answer to that. Re: 6z GFS. I think it is just the strength of the front, orographic lift, and the overhead jet. It also could just be that the 6z GFS is a blip and had more precip on this run. We will know if it is a trend soon. It looks like the convection in the GOM gets out of the way quicker which may allow for the conveyor belt to pick up more moisture. We have all seen the movie before...great forecast but convection fires in the GOM and cuts our qpf in half. The lift occurs on the Plateau and a secondary wave over the eastern valley - think of a wave on the ocean where you have a peak then a valley and a secondary peak. The other lift occurs over TRI as we are just a bit higher here. Points east of I-81 are favored.

I looked to see if there was a wave in the 6z GFS. On the 700 vort map, there is a small piece of energy which is caught on the lee side of the Apps. That could be part of it. The other orographic lift IMO. The jet has to be roaring above. When that hits any amount of elevation, it is going to squeeze precip out. But again and not to beat a dead horse, the front is so strong it is going squeeze precip on its own without the lift.

The GEFS may be right here, but it mishandled the upcoming pattern pretty badly in the LR. The verification scores above actually show the CMC scoring higher than all other modeling on multiple occasions at that range. I lean it’s direction for now. Until the GFS shows me otherwise at d10+, I am weighting it less in the LR. The EPS could be right as that is a phase 7 MJO? That said, what we are seeing sure looks like a reload of the current pattern and it should be as the current pattern’s clock doesn’t really run out until mid Jan to early Feb - 4-6 weeks. if one can ignore the Cfsv2’s cold bias, it’s evolution at 500mb seems reasonable this morning. It looks like the Canadian. The Canadian nailed the upcoming cold pattern and it’s intensity...prob due to its own cold bias. The GEPS was great at 500mb.

As many have said, a front that powerful is gonna have a ton of energy. It should churn out some precip, In addition to the extra precip, the further west that storm gets the more of a window opens for mischief to happen along that front here. I don’t trust the GFS as it failed miserably in predicting the location of the upcoming low. It has moved from North Carolina to Illinois. That said, once it locks in the track...it probably will handle the precip amounts a bit better. As others have noted above, the Euro seems to be missing precip which had been a common bias of that model in this setup.

I truly don't know. The difficulty with tracking systems so far out is that inaccuracy is plentiful. We will know more by Tuesday morning. I think our best chance is for the cold to rush into that front. If the cold hangs up even slightly it is cold chasing rain. However, this front is powerful and the dynamics are going to be extremely difficult for modeling to handle well IMO. We see fronts like this maybe once out of every four or five years.

Flooding is quite common during even the most severe of winters, and so is severe weather.

La Nina years are full of extremes. Take that to the bank pretty much every year we have them. That is what makes them crazy. We are going to be approaching some record lows. The sheer power of the cold will be impressive, even for long time weather watchers. We are 100% fighting seasonal climatology - it doesn't want to snow here until January through early March. We have been spoiled w/ a few early season snow storms in the valley during the past 10-12 years. Prior to that, the valley experienced very few big, early season snow storms - even when I was younger. I encourage everyone to enjoy the potential for snow showers and cold weather for Christmas. It could be so much worse on many levels.