Carvers Gap

The GFS and the GEM (if one extrapolates past 240) continue to tease some big changes just after d10. The NAO is trying to be a player. It backs up the entire flow upstream and basically resets the 500 chinook pattern. Is it right? IDK. If we can get a storm to hit the West Coast near Los Angeles, that might do the trick in flipping the trough back East.

12z suite is rolling. I am going to put my thoughts on this suite in this single post. I will simply update it by editing. Feel free to comment. Just know this post is going to have several comments. So, you might "like" one thing, and it might be followed by something you don't like. Haha. 12z GFS -The GFS is really the first model to correct the Pacific NW. It has beens slowly doing this very several runs. Let's see where this run goes. I generally just toss the run if a slp wonders from British Columbia to 500 east of LA. 6z had a realistic solution. -@ 132 the GFS is flirting w/ a winter event over SE KY, SW VA, and NE TN. Probably is WAA, but tough to tell. Interesting development which I don't think has been there before. -The interesting thing is that there is a hp sitting over the top of that. -@ 195 that looks like more feedback over the Pac NW. Interestingly, there is an EPO ridge forming(temporary?). Definitely seems like this timeframe is a demarcation between a good path back to winter weather and on that is not. -@204 that storm off the coast of Cali looks like it might move inland. Any storm that enters at the latitude of Los Angels has to be watched on the EC. Many times a storm will enter and exit at similar latitudes of NA...not matter how far north our south they wonder while over the continent. -@240 generally I just look at the long wave pattern as details are going to change by the next run. The GFS got lost around 195...and ended up with a much different solution -the Dec 22nd cold front is present w/ wintry precip on its northern edge as it departs...big take away and we'll see if it sticks. -I should add that the -NAO is present on this run, but slightly less strong. The NAO is very difficult for models at range, but can make big difference upstream if they form a block. -As wild as that run got, it pretty much got to the same point that 6z did by 270. -300+ The GFS puts the trough back in the East(temporary?). The run-to-run change graphics for this time frame are gonna be fun - really fun. -On both the GEM and GFS...the NAO is east based but having a major effect on the 500 upstream pattern of all of North America. Right now, the GFS has a window from Dec 23-Dec30 for the chinook. Then, recent deterministic runs tend to slam the door on that by the New Year. The real fun begins is if the 6z GFS run blends w/ the 12z run at some point....chinook muted and then trough into the East. Don't know if that can happen, but w/ the MJO in the COD, the SSW may be taking the driver's seat. The NAO would likely be a result of that. 12z AIFS -Looks remarkably similar to the GFS. Looks like around 300 it wants to send a decently amplified trough eastward. Not sure if that is temporary or not, but w/ the NAO sitting up top...that teleconnects to an eastern trough more times than not with the usual caveats mentioned by Boone and me in early posts.

Kind of wild in the wx model world at 0z and 6z. The 6z GFS cuts into the Chinook lifespan fairs significantly. IF the NAO is a realistic player, it is likely going to turn the pattern after 240 upside-down. It sure did last night on several runs.

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.

The 18z GFS joins(?) the 12z Euro in muting the chinooks with multiple cold fronts. I did notice ensembles beginning to cool off at 12z (look at the run 2 run for reference). I hesitate to say the GFS joins the Euro since the GFS was the first to the party and then went and smoked a cigarette on the back porch at lunch.

I think the trough shifting back NW makes sense given climatology. I also know that LR models like to end winter with that....only to have the entire trough come crashing SE w/ one good cutter. I suspect we have a really big cold snap coming...timing TBD, but I would guess LC has this nailed to the wall.

12z suite highlights. The 12z Euro(surprise!) now carries the banner for cold. The Dec20-30th timeframe for NE TN is normal-ish. It has the least feedback over the PNW. The Dec 19-20 cold front is now a "go" with it being legit Canadian cold. Can we score another front on the 22nd per the Euro - the GFS lost it, but I bet it's real. The really interesting one is the backdoor cold front on the 27th. Yes, it looks like Christmas should be warm with the cycle of warm fronts and cold fronts seeming to have it locked in between cold fronts - but who knows really. At nine days out, anything can happen. Maybe the really big news is the NAO looks on steroids on both the GFS and Euro 12z runs. It is east based, but retrograding to the West. It doesn't take much imagination to see a full latitude trough developing over NA between the Aleutian and NA ridges. A true block w precedent.

The 0z Euro is much different w/ the Dec19-20 cold front potential. I think it likely wrong. The 6z AIFS has the cold front. It would not surprise me to see snow flurries or snow showers behind that front. If you watch the 6z GFS at 500, it makes sense. It pops a ridge in the East. It gets knocked down. The next ridge(chinook) pops further west. It gets knocked down. Each time the ridge goes up, it gets knocked down, and retrogrades westward. By the end of the run, it is a EPO ridge. Jax mentioned the atmospheric river. It may well be we are still in a base-cold pattern w/ the AR overwhelming the MJO signal which wouldn't be unprecedented (reference earlier discussion). As it retracts, that trough would slide right back into the East. I need to actually look at modeling in the Pac to see if that is happening. Interesingly, western Montana has had severe flooding when they should have had snow. Troy and Libby have lost several bridges in western Montana.

The 6z GFS is back to normal for Dec 19-29th after a warm run at 0z. Interestingly, the 0z run developed what appeared to be feedback over the PNW. When that occurs, the rest of the run is warm. When it doesn't occur...it is back and forth. For now, it looks like cold air masses will visit(24-48 hour duration) on the 19-20th, possibly the 22nd, possibly the 24th, and then too scrambled to even guess after that. In between the cool downs, there will be chinooks likely. I am really interested to see where this pattern settles after this transition timeframe. But the back and forth pattern might the the actual pattern for a few undetermined amount of weeks.

It looks like temps (not right by the river) are ranging rom 7-9F for my area of TRI. It is 8 at the airport. We had wind chills yesterday in the mid-single digits.

And be sure to keep posting! Great to have our input...I meant to add that.