Carvers Gap

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.

By 210, the Aleutian high is back....the question is will it rotate eastward as the trough digs SE. If so, and EPO would pop.

At 204, it appears the cold front has sped up a bit...let's see if it makes it all of the way through.

Just because it is a slow night....will talk the 0z GFS By 189, there is a continue trend of disrupting the Aleutian high. Trough would appear to be headed eastward...we'll see if we don't get a cutter first.

That pattern I just posted looks remarkably similar to LR modeling today...and also to Feb 20'. One was a nada and one was a La Nina. One was a dud and the other was historic. @John1122, very interesting about LA and great post. I have always considered storms coming in at the latitude of LA a good thing. That has not held true so far. I have held to the rule of thumb that storms that enter the west at a specific latitude normal exit on the east at a similar latitude. Not always true, but wonder at some point if that works in our favor.

Yeah, I kind of stumbled into the Feb 20 thread. Pattern looks very nada right now...similar to that. Here is last year's pattern that ran up to the big storm.