Carvers Gap

This may just be a case of climatology taking over(January is our coldest month). We don't need as many things to be exactly right in order to get cold. We'll see. See all of those AN heights at 500 and so much cold at the surface is counterintuitive. So, wary I am.

@tnweathernut, looks like the first significant disruption of the AH begins around Dec 30/31 if modeling is indeed correct - between 120-130h. Looks like a couple of storms crash into it. Almost immediately after that, the area of hp loses its uniformity and lifts out over the next few days. And you are on the money about whether this is correct or not...just tough to know. I think this scenario very possible, but not ready to take the step and say it is likely. 18z GFS again with another flip of the pattern. Agree also it could be rushing, but other modeling seems to be there with it. What is crazy on this run is that NA gets so cold that the AN heights at 500 are still cold at the surface and the BN heights are even colder at the surface. What looks warm is just "less cold" air getting moved around. Not sure I have seen that on a map in a long time. At the end of the run, there is this big ridge in the central US....generally below normal at the surface with another shot of cold incoming.

Will just use this post(update as the run progresses) to cut down on tons of posts for the rest of the 18z run: -Hudson Bay high will drive this pattern for the rest of the way along with what would seem a very -AO. -By 288 the big red blob over the Pac is adios'd -The Hudson Bay high will force the storm track well south if real. This would be an Atlantic dominated pattern if real. Check that...AO dominated pattern and a HB high dominated pattern. -Europe has turned sharply colder by 288 which tele connects well to cold temps over the EC. -1068 high coming down out of Canada around 300. Super smiler to both the Euro and CMC which had monster highs coming down. -Fairly massive Arctic outbreak being modeled after 300. -This is 2020 February 2.0 light...yikes -Pretty epic run as at one point roughly 1/3 of the US (mid and upper Plains, Rockies) are below zero.

18z GFS does indeed begin to severely erode the AH immediately after 240. Going to be some crazy cold air coming into the Lower 48 this run it would seem.

18z GFS to a lean towards the 12z CMC with the cold front on Jan 3rd. Temps are 10-15 degrees below normal. Let's see what it does with the AH this run. Looks displaced already. Pac Ridge has connected to the NAO....stage would seem to be set or a fairly southward displacement for cold air on this run.

Past week or so we have seen an increased frequency of the AH(tired of typing Aleutian high) to lose some steam on LR modeling. Last night, JB mentioned the EPS may be hinting at the MJO firing. The IO has little convection. Need it to fire in order to push the MJO along. Right now the maps look very much like a phase 7 which is pushing near 8. Looks like we may potentially have a window for tracking between the 3-10 with the window between the 6-8th having the most promise. Crazy thing, nobody remembers those great Niña winters if you subtract 10-14 days of cold during those winters. Just need the pattern to relax which it may. Great discussion today by everyone!

I suspect we fight that Aleutian ridge all winter...There is a reason people out West absolutely love La Nina winters. Weak La Nina winters here(southern Apps) can be very cold at times(maybe even as a general rule), but not always. People on the EC don't like La Nina winters. West of the Apps it can work. We don't need super cool weather in early January to have a chance. Just need seasonal. Right now if forced...I would way the trough lifts out around the 10th. However, what happens after that is really open for debate. Does the Pac ridge reform or does another trough drop into the center part of NA? It has been my experience that La Nina cold comes in waves. Usually the dam releases, a ridge builds back in, and we are fortunate, we get a second shot later in Jan or early Feb. I was going to note that if you watch carefully, there is almost a large cyclonic flow over all of NA. The cold crosses the pole from Siberia which sees NA, is forced against the Rockies where it creates a huge cold air mass, warmth builds over the south, and the cold release SE once there is enough of it. So you get pulses of cold which head SE. A lot of those fronts wash out right as they hit E TN. The cold if it can get something to move it quickly, is often well below normal. You subtract those 2-3 weeks in 84-85, nobody talks about that winter. That cycling flow, if it stays in place, would keep pulses of cold in the pattern for as long as that "feature" is in place.

Really, because we cannot see past the 10th...can't be sure if this is a pattern change or just the PNA relaxing as a result of the Aleutian ridge weakening. The Aleutian ridge could restrengthen. We need the current block to reconfigure just enough to allow the buckle in the western jet to swing forward. That either is going to have to happen with a weakening of the ridge in the Pac OR (and this may seem counterintuitive and may even be an error in my thinking) a slight weakening of the NAO. I have been watching this very several days. When the NAO weakens just a bit, the trough kicks eastward. Only problem, it lifts right out with no block in place. So, we need the NAO to weaken just enough to allow the trough to slide underneath, but get get blocked and not allowed to scoot out. That may we an error in my part....but that NAO needs to soften up just a bit. But.... we still need it. AO may be the driver going forward.

The BIGGEST thing I thought was interesting....watch the Aleutian ridge on all three of those operationals. What do you all see?

Not Jax or Holston, they are the SOI gurus...but when you see the SOI move like that....all kinds of movement occurs regarding hemispheric flow. IMHO, usually means a sharp pattern change would be under way. Now, we may or may not like the end result of that pattern change, but that is usually a signal of things switching up.

Anytime, the SOI jumps like that...usually a big shake-up ensues downstream. Also is true in reverse. Things start moving. We don't want the SOI in strong El Nino territory. Santa brining the goods(meaning the gifs). Thank you!!!!

All three 12z global operationals reverse the current pattern over the lower 48 in one form or another...and especially off SW Alaska. The Aleutian ridge is currently digging a downstream western trough which is forcing a SE ridge. The weaker that Aleutian ridge after Jan 1, the weaker that SER and the more the cold pushes. Everything hinges on that ridge being displaced, removed, or weakening. The bigger development is seeing the GFS pop a +PNA. Euro has something similar at 240 with ridging building out West. Canadian just puts all of NA in the icebox.

Looks like the Aleutian ridge weakens more on the 12z EPS. Great thing is I think the EPS is getting into the part of the season where it is a bit more trustworthy - maybe. LOL. Operationals are very cold. Trends are good right now in regards to the Aleutian ridge. The GFS has been leading its ensemble for a few days....and it is a total pattern flip. For now, looks like a decent window for winter wx between the 3rd and 10th. Could definitely change as that is still a ways out there....key is the weakening of the Aleutian ridge. That SOI bump may do the trick. Do you have the gifs for the 12z operationals handy?

One potential we may see Went and looked it up. Below -8 is El Nino. Above +8 is La Nina according to BOMM. So, basically we have been in an El Nino SOI state( @John1122all over that) and now we are returning to a Nina(edit) state. That jump is going to create a shift downstream. Just looking at ensembles. Looks like the trough just goes nuts over the East for about 7 days beginning on the 3rd. Looks like that is decent window for storms if the STJ will stay as active as it looks. Then, potentially the trough lifts out....not convinced that is actually what happens but it could.

The 12z EPS is now very close to being in that CMC camp from a few days ago. Good trends. ALWAYS wary of the rug being pulled out...but seeing BN temps at the time when it is climatologically coldest is cold indeed.

The 0z Euro control, which has kind of been leading the ensemble for the past few days, is quite cold after the 3rd. "Bitterly" might be too strong of a word....but it is headed there.

The 12z EPS is much cooler through 300 than it was at 0z, and 0z was not too shabby.

That is Nino level, right? Like strong Nino? Would also be indicative of a pattern flip over NA pending I think. That is craziness. What is your take on that, Jax?

12z CMC is better in terms of the pattern here. Snow on the 3rd and then a cold period follows.

12z GFS with a complete pattern reversal again in the LR. The erosion of the Aleutian high begins around Jan 1 and is eventually replaced by a trough. PNA ridge replaces the strongly negative PNA. Likely the GFS is jumping the gun, but a fun run from a 500 pattern perspective.

Couple of general and finer points this morning in no particular order: 1. The Aleutian high is weaker, displaced from its current location, or completely gone in the LR depending on your model of choice. 2. The EPS teleconnection for the PNA goes from extremely negative to nearly neutral - positive on the control. 2. Pattern itself may become one dominated by -AO. Maybe the -NAO for at time as well. EPO showing some signs of cooperation. 3. Tough right now to say whether we are looking at a pattern reversal, a temporary relaxation, or simply 4-5 days of cold. If we hold to patterns lasting 4-6 weeks as a general rule, the current pattern is due to change during the first two weeks of Jan. That doesn't mean the new pattern is any better. I think it is possible on modeling that we are seeing the beginnings of that shake-up. Just tough to know where all of the pieces end up once the current pattern begins to erode. 4. The first cold front to set this in motion may well be Dec 31st. It is not overly powerful, but could potentially knock down the much above normal temps behind it. The Jan 3rd front could be fairly strong, but that is not a given. 5. Lots of things in motion this AM. Truly those have been seen on modeling for about a week, but we can "see" those changes now on operational modeling. Word of caution is that the base pattern seems to really be a trough in the Mountain West. However, the cold temps being modeled at times is just insane. There is a mid-1060s hp at the end of the 6z GFS run over MT and the front range of southwest Canada. That will change, but it shows the extremes on modeling right now. So, lots of stuff to get worked out. 6. Big takeaway is that extremes are on the map. If the Aleutian high weakens which in turn will weaken the monster -PNA...the cold has a legit chance of coming eastward - likely in waves with very warm temps between waves of very cold air. ALL OF THAT IS SPECULATION RIGHT NOW IN TERMS OF THE LR PATTERN. 7. addendum: The MJO is just crawling across 7...it is in no hurry. Several of the maps look a lot like 8. But work remember what John noted about low amplitude 7 a few pages ago...that is a cold signal for Atlanta.

Good morning and Merry Christmas!!! Fingers crossed, ensembles and operationals (speaking in general terms) are continuing the trends from yesterday. Let's see if those trends continue at 12z.

Hate to gum up the thread with a million posts about LR modeling...but the Canadian is about to go bonkers in terms of cold. Will simply post my comments here int this post so as not to add 10 more posts. If the 0z GFS had not feed back into that trough, this is likely what would have happened. No idea which one is right, but that looks an awful lot like what happened last February. Wow. Likely too cold, but the CMC has single digits over northern portions of the forum area with no snow on the ground which is impressive. We have seen these types of looks before....Head fake? Plausible scenario. Extreme swings? Also a plausible scenario. We have seen both head fakes and wx extremes during the past two winters. If the elimination of the Aleutians high is legit, we could see a November-esque pattern develop but I am way ahead of myself with that.

Indeed post 300, the GFS again simply gets rid of the Aleutian ridge. The gradient between Kansas and northern Montana would something like 80F to sub zero - very sharp. Trough likely goes into the east again as it did at 18z, but just a bit later. Just one run and likely will be different at 6z. It is now officially Christmas!!! Merry Christmas to the best wx forum in America. Hope everyone has a great day. I will try to post some, but tomorrow will be busy. Keep the home fires lit.

When I talk about pay me now or pay me later with that big ridge hooking into the NAO....If memory serves me correctly, the reaction during past years has been quite abrupt regarding the TPV - not the usual waiting game for an SSW to propagate downward. Now, I am not sure this run is even realistic given the aforementioned feedback, but in the off chance this is even closely correct....cold air would likely be jettisoned towards the mid latitudes quite quickly.