Carvers Gap

The 18z AIFS has a -EPO ridge at the end of its run. A lot of this looks like SSW signals - hints of HL blocking.

I think what we will see is the MJO slide into phase 6 as the NAO fires. The mid continental ridge will hook into it briefly. That will create a significant SSW. The MJO will slide into 7-8 as the CHI charts showed over the weekend. The entire cold air mass gets released into a full latitude trough over the US w/ the storm track south of the Ohio River Valley. Good sign if it holds. The NAO will work against us at first, but as it matures...that is when it pays off.

Wow. If that NAO is real on the 18z GFS, it very well could force split flow...and you kind of see it at the end of this run. That will completely upend modeling over the next few days if legit. That would be a major player. The 12z AIFS and 18z GFS now have this.

By 200, the NAO is having significant effects on the run compared to previous runs. The 12z AIFS scores a coup if it nailed it first.

That is a big time NAO on the 18z GFS run. It doesn't have a lot of impact yet, and its staying power is TBD. It may be a forced NAO which just results due to dynamics and is passing through, or it might be the SSW finally working its magic along w/ the QBO. It could hook into the mid-continent ridge, but that generally would cause an NAO and subsequent cold outbreak about 3 weeks later...and has been a common feature of winters of late.

Yeah, cold and viruses have been making laps in my crew. Pretty miserable stuff and hangs on forever as @Daniel Boonenoted. Hopefully the 12z Euro Weeklies are right and we see cold return right after mid-January. The 12z CFSv2 breaks for cold at about the same time. It looks like when the NAO fires(if it fires), that puts a clock on the chinook. Maybe if that NAO can fire earlier, we can return to a colder pattern more quickly. But really, I am good with a couple of weeks of warm weather. Something makes me think the dam is gonna bust at some point sooner than later. One good cutter, and it could all come south.

The 12z AIFS pushes back pretty heavily on the chinook - even more so than the 6z GFS. Take one look at the 500 map, and it doesn't look great. But take a look at what is creeping into Greenland. That is a game changer if it stands(and doesn't connect to a WAR). But take a look at the surface. Not what you would expect. That isn't warm. Cold air is seeping into the EC. A cold hp over the GL is not a bad thing for us. FWIW, the 12z GFS looked ready to break the chinook look by the end of its run. The NAO firing will force everything south.

I will say one thing. The flu is gaining strength in some areas. The blessing of any warmup would be to get people outside some, and get some air. Flu and cold outbreaks go hand-in-hand. I don't think the flu shot has been working super well this season. I will take a chinook over a house full of kids with the flu!!!!!

This is kind of what I am talking about. Two cold fronts are now firmly present right in the middle of the Chinook. Originally, it was torch city. I wouldn't be surprised if some didn't see a snow shower or flurry from this. The 12z GFS won't be as cool as the 6z as it gets bogged down(guess where?) just after 200.

One thing to watch is how wx modeling responds to potential negatives from the NAO/AO couplet. I highly doubt those details are worked out. Now, an NAO during mid-December is pretty meh in my book, but later in December...it could help. Evidently, I cropped the model information from some of these. The first is the GFS 6z AO plot. The second is the NAO for the 6z GFS. The third is the 0z EPS for the WPO. The fourth is the EPS 0z NAO. The fifth is the AO for the 0z EPS. Those are not bad teleconnections for us. Let's see how modeling builds those into their looks for the medium and LR.

I also agree the WPO has been a key driver so far this winter. JB has mentioned it a lot. It has been extremely fickle to predict out past two weeks.

The 6z GFS, right on cue, again cuts into the chinook look. The CMC is now on board with this as well. One thing I am noticing in modeling is that across the board it is greatly modifying the warmth as it draws closer. We have seen this happen(in reverse) when advertised cold air masses(which are supposed to last for days....modify and are merely a frontal passage. Right now, the 20th and 22nd look ripe for decent cold fronts. Is it possible the deterministic models were to quick in bringing in the chinook and it still may materialize? Maybe. The chinook pattern has been pushed back by at least 10 days by my count so far. I think it likely we see some chinooks, and some inevitable warm days. I mean, we are due some warm days. TRI has been BN since Nov 26 - every, single day. That is a stretch of nearly three weeks without a single day AN. We live in the sub tropics - it is going to try to get warm in a multitude of ways. TRI has recorded a trace or more of snowfall seven days this month. IMBY, that probably adds up to maybe a couple of inches. The number of days(not the total) with a trace or more is way AN. Right now, TRI is -6.8 to start the month. As for 84-85, JB mentioned it last week. I didn't bring it to the forum with much discussion, because that is a landmark winter. I did mention it to one poster on a sidebar to record the thought, and see what they thought. I pulled the 500 pattern to look at it - made the map myself. The 500 pattern looks exactly the same as the next four weeks on LR ext modeling at 500. It is another reason I have been saying to be careful not to cancel winters. And hey, we may go the way of dreaded '89, or we may score like 95-96 or we may chart an entirely new course (more likely). With so much cold available, all it would take is a decent NAO or EPO(even temporary)...and it discharges. I don't think we go 84-85...but 95-96(light) would be the ceiling in my book. But I think the hand wringing over an inevitable warm-up after three weeks of cold is not something this forum has traditionally taken part in, and hasn't this time. We pride ourselves in not devolving into group think. I also think it very important to look at model biases, and learn to factor those into thinking. The Pac NW feedback is real, and it likely caused erroneous solutions at least for the dates Dec 15-22. The repetitive Baja lows never materialized earlier this month - feedback error. Let's see if that continues. Infinite loops are real problems in computer programming, and wx models are not immune. There is one other winter where this feedback occurred. I will try to dig that winter up today. Our conversations were almost identical as now. I have noted many times. In the IDF(Israeli Defense Forces), if everyone agrees...one person is required to take the other side. It prevents mistakes. I am thankful this forum doesn't try to drown out opposing viewpoints. I think we do a pretty good job of that. That is what makes our forum strong.

And it could end up being warm. But in the end, it is just something none of us can control. The thing that will irritate me when tracking winter patterns....a model flip away from a cold, storm pattern. In this case, the chinook pattern has been well advertised. What I want to see is that pattern to be muted. Modeling is apparently going to miss at least two cold fronts...maybe more. Those fronts are getting colder as reality approaches. That is a sure tell that modeling is correcting. There is also a bit of a disconnect between 500 and the surface. So, interesting times ahead. Prim climatology is still almost a month away. And yes, I could use a few warm days just to thaw out. It has been BN here since Thanksgiving...I need a break from the cold. You won't hear me say that often!

The surface pressure anomalies are not bad throughout.

Have to look at the surface. 500 maps are missing cold shots. I think we are going to see a fairly normal pattern for December at this latitude. What I am looking for is not non stop chinooks. I am resigned to some chinooks mayhem. We were close to a winter storm that run.