Carvers Gap

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.

Oddly, the problem this run is that the NAO is so strong(big change since 18z and maybe not a great change) is that the NAO just bottles up the flow. I think it still gets to where 18z did but a day or two later. The mid continental ridge feeds into the NAO in a pay me now or pay me later pattern regarding cold. That big ridge is a tell tale sign of an SSW that would almost certainly disrupt the TPV and SPV.

Though the 0z GFS is a much different variation, after 300 it is beginning to weaken(or eliminate?) the Aleutians ridge again. If that trough doesn't free back off the coast of California, it would flip the pattern again...may still yet do it. We'll see.

Looks like there is problematic feedback within the model with the storm that drops southwest out of split trough(?). It should recurve toward the coast a bit more quickly which delays the downstream response over the eastern US.

One recommendation...With so much cold, it is wise to actually look at surface pressure departures and surface anomalies. What looks like a warm map at 500mb can actually be quite cold at the surface sometimes. 500mb is roughly 16,000-20,000' above sea level. Definitely truly on the 0z GFS.

Merry Christmas to everyone!!! Though warm, it is a beautiful night here in NE TN. Watching the 12z GFS roll-in. Yet another variation of the Jan 3rd event. Cutter and this unleashes very cold air between the Rockies and the Apps.

The 18z GFS again flips the pattern...just switch the blues and reds on Tropical Tidbits over the US in the LR. Basically, the Jan 3 cold front begins the flip w a transient ridge after that cold front. No idea if that verifies, but impressive nonetheless. If a pattern change does a occur, the CMC and CFSv2 score the coup.

Grabbed this from the MA forum...great write-up about the potential seen today in modeling by @brooklynwx99

General trend across the board today(operational and ensembles) is to weaken, severely displace, or completely remove the Aleutian high. Opens the door for cold if true. A true MJO 7 would allow for that. As John noted, the atmosphere has been more a 6. Generally speaking, seeing a large area of BN temps slide eastward and expand between the Rockies and the Apps. In between Christmas activities, so hopefully this post hasn’t missed something major! LOL

12z EPS is a fantastic run and ensemble at that. @jaxjagman, hang in there. Glad it is getting better. Great to see you on the forum more.

Guessing the GFS is jumping the gun, but the continued erosion of the Aleutian high is apparent on that model yet again.

12z GFS is a complete pattern reversal. Its ensemble, while not a pattern reversal, is winter.

Thanks, man. Hope you and your family are doing well. Is Nina expected to last through winter or move to neutral?

The 0z European control lifts out the Aleutian's high, and temporarily reverses the pattern downstream. We have seen that look on a few recent GFS runs, notably the most recent 6z.

So something to watch is the breakdown and/or weakening of the Aleutian high. The EPS is very aggressive with this. I ned to see a couple of more runs before I give that look credence. However, the GEPS is similar. The reason the GEFS is an outlier this morning among the big three global ensembles is that it is slower to weaken the high. However, the trend across the board was to weaken the Aleutian high overnight(in the long range). Let's watch and see if this is a trend. This is the time of year when the EPS begins to rule the roost. So trends on it must be taken into account. Could just have been a blip due to data input or could be the beginning of a trend. Just don't know right now. One other thing to watch, and the Euro Weeklies had this yesterday, is for the cold to push under the SER. That is sometimes a mistake by modeling to depict that, but it can happen during January as climatology(favors stronger cold across the northern hemisphere) supports colder air masses which can push....

That is an El Nino signal right, and strong at that?

Oddly this AM, the warm biased EPS has a nice set-up from the 3rd forward with a ridge rolling through during that time. Will wait and see if it holds at 12z before discussing further. Right now we have the EPS/GEPS with colder solutions after the 2nd with a ridge rolling through after the cold shot. That window around the 3rd has some potential though the window is tight.

We get back to what Typhoon Tip talked about several years ago which is the SST gradient between an ENSO event and surrounding waters. The gradient has to be sharp for the analogs to work. Additionally we have not seen a lot of trips through 8-1-2 with the MJO either due to the IO or other reasons. I would probably disagree that we have seen a true -NAO show(Davis Straits) up at the proper time until last year. Having a -NAO that lasts most of the winter is a rare thing. I definitely agree that the trough tucked into the West(under an EPO ridge) has been a strong commonality for roughly four years or so - regardless of the wx pattern. My personal opinion is lack of SST gradient and convection in MJO zones which less than advantageous. That said, what we have seen IMBY are quick starts to winter which fade. This year, that cold came in November. The trend here has been early snows, even as early as Halloween. Last year, even with a similar pattern as this year, we still managed a historic ice/snow storm over the forum area. The other thing this winter is just how cold Canada is... I suspect that we see a bit of a scaled reset of Pac SSTs after this La Nina. We have had good winters after La Nina cycles. Why? Water cools and the gradient for the Nina which is surely to arrive next has a better gradient.

Going to hit the sack and will end with this, there is a lot of precip running that boundary after the 30th. If it manages to get colder, that event has low percentage chance of being a frozen event.

0z GFS is a strung out mess with vortices all over the place....like I said, be ready the next run will change.

This GFS run will revert back to a strong Aleutian high. Trough may rotate through after the cold front on the 3rd. Feature that seems kind of new is the vortex over HB which is spinning cold air southward. That cold work. Let's see how that works in future runs. Been there for several, but is seemingly more pronounced with each run.