Carvers Gap

I am going to try a new way of posting. For the 12z suite, I am going to put all note here instead of 5,000 posts in a stream of thought fashion. I will simply edit and amend this post as the 12z suite progresses. Feel free to comment! 12z CMC...is having nothing to do with a prolonged warm-up prior to 240. It has the Dec 20th cold front. 12z GFS...Doesn't have the 20th cold front, but has one on the 23rd. The 12z GFS...gasp...erases the furnace by 276. JB mentioned that last night that all it will take to dump more cold into the East would be for a piece of that trough to split and head eastward. That is the 12z GFS. haha. The 12z GFS has snow showers along the Virginia apps on Christmas Eve. What a turn of events. Feedback. Have I talked about that? Well, the deterministic models (GFS and CMC) have less of it over the NW. That, in turn, reduces the raging chinook which develops with west-east flow. It really isn't a problem to have a ridge roll through in front of a NW PAC slp. It is a problem when that slp spins, reforms, spins, reforms, spins.... With that feedback loop lessened, the trough gets kicks eastward and an Alaska ridge pops. The MJO plots on CPC are much more favorable than the previous days. That may be why we are seeing more cold fronts on medium and long range modeling. Will we see a complete reversal of the heat wave back to a cold shot? Probably not, but just a normal ridge or two rolling through is not a huge problem. If I was waiting on cold and saw the GFS/CMC begin to eat into it the way they just did the warm spell...I might call that a can kick and question whether it actually comes to pass in large quantities. To me, this looks like a back-and-forth pattern w/ a great cold source which comes eastward with any kind of amplification whatsoever. Good trends. I will have a separate post on the Euro if it is similar. Feedback on the GFS 300+ is pretty apparent off the West Coast. If that is feedback, the trough roars into the East. ---> almost the exact some thing which led to the head fake(warm up) for earl December. It pumps the ridge in the East. Without out, that amplification is less or absent. When we see a storm exit Washington state, drift southwest with no steering, and it amps up...that doesn't look realistic to me per the GFS. If that gets worked out, a colder east is possible and even likely.

@Holston_River_Rambler, you jump right in here with your nifty short range graphics. I don't want to be taking your job! Here is the RGEM right before the map above. It dissipates as it heads south. As we so overnight, sometimes it hold together. So, let's watch the trend on this. The 3k NAM is generally just a higher elevation event. With such a strong air mass coming in, the jet streak with this might help. Also, a lot of models won't see lower level moisture getting squeezed out w/ below zero air masses. This might be 15:1 or 20:1 type of stuff.

The 12z RGEM "almost" has what looks like a gradient type anafront which comes in early Sunday morning. By Monday morning, temps at TRI are below zero. I am posting the precip map for Sunday AM and real feel for Monday AM.

1-1.5" seems about right. Some areas have a lot of melting. Raises surfaces did well. I ran this morning in the snow(no complaints!), and the pedestrian bridges were all slick w/ about 1-1.5" of snow covering them. Honestly, this morning felt about 10x warmer than recent mornings. I need about a week long stretch of warm mornings! Nice to score on a clipper for once in Kingsport. Haha!

What is wild, I normally don't look to the MJO as much of a driver in December. The PDO is really what we need to help us. If that can come up for some air, then the MJO takes a back seat.

Yeah, it was a good pop for sure. LC has been adamant(and right for the most part) so far this winter. Looking forward to his updated Saturday night.

I just think we are fighting climatology at this time of year. The deeper TRI gets into December(as evidenced by the sneaky system overnight), the better chance we have at lower elevations. I would suspect the NAO will fire at some point. I "suspect" the worst of winter probably sets up shop in the northern Plains which is not always a bad setup for us. International Falls was a number I watched as a kid. If it was cold there, I knew cold was coming here! That didn't always work out, but that was my "teleconnection." During the 70s, we must have gotten a lot of sliders. I always watched Memphis as well. If it was snowing there, it made its way to Knoxville where I grew up. My general rule of thumb was trying to get one snow before New Year...if that happened, then winter was on track.

89-90 is definitely a concern during any winter where we start fast like this one - lots of cold and snow. That said, this winter just seems like it might have some more fight in it. I always remember 95-96 not being overly cold, but I was in Knoxville. We just hit jackpot with every cold wave. The storm track was nearly perfect by January. I kind of divide my winters up like this. Pre 1990 and post 1990. Post 1990, I really enjoyed 92-93, 93-94, 09-10, and 14-15. Whichever recent year we had that howler of a cold front hit on Christmas Eve..that was fun. Prior to 1990, I just remember the 70s as generally having several consistent winters, and of course 84-85 which is my favorite winter of all. Lots of negative QBO winters in there, and that might be our saving grace this winter as well.

Traditionally, you all "should" do better if/when the cold returns. Here in NE TN, we normally have to hit early with regards to La Nina winters. Middle and west TN should get some chances as the SER should help your storm track. We are fighting climatology IMBY regarding snow this early, but December is usually better for E TN folks during Nina winters w/ some notable exceptions. I picked up about and inch or two of snow this morning which is a bonus. Anything before Christmas here is bonus. I have kind of resigned myself(due to recent winters) to January thaws. That said, La Nina winters tend to deliver extreme cold at some point. Sunday and Monday should be cold w/ wind chills in the single digits for some and light snow showers. I don't think that will be the worst of winter. I would guess we see 1-2 weeks of cold by late Jan or early Feb. As for where this heads in the medium range...really tough to know. Models had early December cold. Then, they flipped warm. Then, they flipped back cold again. Model feedback was a problem over the Baja then, and I think the Pac NW now. I kind of suspect we may see something similar(feedback issues), but that voice in the back of my head also notes it could be a pattern shift. The chinook looks like a lock. I normally roll with 4-6 weeks per pattern during winter. By the 20th, we will be right at four weeks since we shifted to an eastern trough. During recent winters, we have had pretty stable 6 week pattern cycles. We are likely looking at four weeks cycles right now, and the Weeklies sort of show that. Both the GEFS ext and Euro Weeklies have temps back to normal by mid Jan. Larry Cosgrove has been adamant that winter would be at its worse from late January through March. He was saying this while the weeklies were cold and warning of a December warm-up along w/ muted cold. He may be about to score a coveted seasonal forecast coup. Great to have you posting.

Ripping pretty good!

Interestingly, several overnight runs found another cold front(strong on Euro) right around the 20th. It sure looks like another front is gonna roll through on the 26th. So, maybe this won't be a full on torch? IDK. Modeling today and tomorrow should either erode the warmth or lock it in after the 20th. Last night is a good example of what cold fronts can do during winter, and how modeling can indeed miss. Congratulations to @Holston_River_Ramblerfor going with the thread!!! Sunday looks like the next chance for a sneaky system. I gotta be honest...I wouldn't mind a few warm morning to run. I am gonna need moderation after Sunday/Monday.

Welcome to the board. Tell us more about the PDO going up. I haven't even looked at it lately!

I am waiting to see if new WWAs are posted. Almost would have to be.

What is the timing onset for TRI(if it gets here) tonight? I haven't even bothered to look!

The 12z CFSv2 also lends some support to the "jail break" cold pattern potential just after Christmas.

Here is a prime example of the ensemble mean being skewed by anomalous members. I mentioned this yesterday. A substantial number of members from the EPS(2 sets of panels) and the GEFS (1 panel), have a cold front coming through on Christmas or the day after. The first group of thumbnails is from the GEFS at 366. Most of those members have a cold front pushing through. The EPS also has several members which produce cold. Surprisingly, the 12z GEFS has more of colder solutions. (I am pretty sure the GFS and GEFS were not updated at the same time. That leads to some discontinuity between the two at times.) This "could" be the first chink in the armor of the duration of the presumed, longer-duration warmup. Time will tell. In early December, the first signs that modeling was reverting...the oddball deterministic run which became more common and individual ensemble members.

Somewhere, Larry Cosgrove has to be smiling. The Euro Weeklies have a strong EPO by about Jan 17th. So, we need to weather the storm between Dec 20 and Jan 20. It seems like the patterns this winter are not as stable as past winters, i.e. they are shorter in duration(4 weeks and not 6 weeks). If we can swing a cold air mass or two during that "warm" time frame, that would be awesome. If we can find a way to go cold during that time frame, we have a shot at a cold winter. We are all pulling for the 12z Euro to be a trend and not a blip. It does actually have support from the 12z GFS which is just about 48 hours later w/ the trough pushing east. But huge grains of salt at that range.

I think it is a really amplified pattern. That is Arctic air under that ridge...1054 hp sliding down the Plains. Deceptive look for sure. Cold air is traveling close to the surface...some of the coldest air of the season under that ridge.

Not clipper, but interesting I think...The 12z Euro loses the infinite loop feedback over Pac NW. We saw something similar w/ the repetitive and erroneous Baja lows earlier this month. The 12z GFS got locked into a Pac low(maybe it is right?) complex, but the Euro kicked the trough eastward. Take a look at the differences. There is cold air drainage into the NA Prairies on the Euro. Compare that to the GFS at the same hour. Now to be fair, the GFS eventually kicks everything eastward. I think anytime we see a standing ridge over the SE this winter, we are really going to have to question what is going on upstream. Those ridges can happen and there is precedence. But they have been mirages this winter. I do think a Chinook is coming. But until the PAC NW repetitive low situation gets resolved, everything after that is probably a crap shoot. BTW, infinite loops have always interested me, mainly because they are a pain to programmers. I had to take three programing classes at UT. Infinite loops were challenging puzzles to solve, and sometimes a huge pain in the you know what. We really want to be routing for that 1050+ hp to continue to show up on modeling. This could be a blip, but worth watching.

Bring me some snow, Holston.

We saw this EXACT thing happen already in this short winter. I referenced my erroneous Nov 21st post yesterday(which caused some confusion). Let's see if the Euro stays with that solution. But the 12z Euro is a great example of what happens when things don't stall or feedback over the Pac NW. I have little doubt the GFS is having trouble in that region, but I don't remember it having feedback issues w/ troughs there. It does have some issues with building up cold air masses in the Canadian Rockies front range and then not kicking it out. But w/ the comparison I had above w/ the snowfall amounts vs AIFS, the GFS is an outlier at this time. Now, it can snow out there big time, but it really is out on a limb. When the trough doesn't stall there, it "should" kick out which it did on the Euro. The bad thing about that possible error is that it absolutely wrecks LR ext (weeklies) until it gets fixed. And if we are looking at 1055 HPs coming out of Canada, that would explain the models bouncing around.

I will be interested to see if CPC updates their official plot. I honestly don't know if they derive their own plot or get it from ABM. I haven't ever thought about it. Thank you for clarification on that.

I "think" the black line is the observed index. The black line is the same on the Euro. The starting points for the model are the 11th. Prior to that I "think" is observed. It is possible the CPC site corrects that later? I haven't really watched to see if they change it, but I don't think they do.

The 12z Euro slides a 1052 hp into the Plains late in its run. Wild swing. I will post some graphics when my stuff updates.

The 12z Euro (it hasn't run on WeatherBell...but has on pIvotal) gets rid of the infinite feedback loop and kicks a strong trough into the East and completely flips the d10-15 pattern. Is it right? No idea. But I feel like I have seen this movie before....like about 2-3 weeks ago.