Carvers Gap

Just tagging on to @Matthew70's post...Here is the Euro Weeklies (ensemble) make from a week ago and compared to todays run for December 30th. There is a PNA ridge which is likely just temporary. There is a -NAO whose duration is TBD. The Rex block relaxes. This could easily flip back, but that is big change. Want to guess what caught the trend? The Euro control of all things. The extended version of the deterministic run possibly sniffed out out this cold front at full range(360 hours).

Digging through ensemble members. It looks like there is potential for another strong cold front on Jan6-7 - per GEFS. This looks like a very active pattern coming up in regards to cold. Let's hope some precip can work its way in. I would think clippers and NW flow would be on the table for even norther portions of Gulf States IF that pattern verifies.

I know this is a bunch of posts and my apologies. The 12z para GDPS goes back-to-back w/ cold fronts beginning w/ the 28-29th. We could certainly be cold and dry. That is with precedent. However, the storm track should be suppressed with this. With the return flow behind these fronts, one would think at some point either the cold air doesn't get out of the way(over running WAA) or the warm air doesn't get out of the way. To me, the para GDPS is a logical path forward, but by no means not the only one.

Take a look at the difference in on the ensemble between 18z GEFS yesterday and 12z today...I have been griping about this for weeks. This is for Dec 28-29. There were a few really strong warm air masses embedded in the ensemble mean. They were greatly skewing the mean - even though there were a greater number of colder members included. As we get closer to the event, the anomalously warm air masses are subtracted. And we get this substantial move. Do I still think we see chinooks? Yes, that seems baked in the cake. However, this may we a winter where the colder air masses get colder as reality gets closer. Those are kind of fun winters BTW. We don't get a lot of those. Normally, we see cold air masses moderate as they get closer to reality - Ex A is early December. To be clear, I do want to see a few more runs before declaring the Jan 2-3 cold air mass has legs. If models are flipping this much, they could easily flip right back.

The gradient boundary presses further and further southward with each passing surface wave. If we can line up precip on an east-west boundary, we could see a slider in play.

Just for kicks and giggles...12z AIGFS gives us this look. That will certainly change, and was a red herring in early December. However, IF the second cold shot is real, I would certainly think winter wx might be on the table. At some point, one of those warm air masses with lots of humidity won't get out of the way fast enough.

The 12z AIGFS(no idea how accurate that model is???) also sends a pretty strong cold shot around Jan 2-3. It is more Texas centered, but spreads eastward. It has an anafront - there is that word again. Models were overly strong w/ the early December cold. We have to guard against that, but this is January. Climatology favors colder air masses.

Here is what is interesting. The Euro doesn't see cold...until it does. When it finally gets it in its crosshairs, we usually are good. So, on to the 12z Euro....There is a cold front on the 28th which is getting colder with each run - thanks to @GaWx for the ensemble info. The Music City Bowl...moderation of temps would be appreciated(Dear CMC). I about froze at the Vandy game w/ a stiff little 5-10mph wind in my face in the South end zone. In my younger days, no problem. Back to the point...the Euro has another cold front on the 2nd which looks legit cold. General takeaways....IF the NAO is in place and has staying power, it very well could pinwheel one cold shot after another w/ warm interludes. It would force that cold well south per @Daniel Boone's comments - I agree. Those were some WILD runs at 12z. Want some fun? Go look at the 500 map for the CMC at 240. Then, go look at the surface pressure anomalies under that. Then, go look at temp departures from the norm. Single digits sitting under a monster 500 ridge. How does it doe that? Welcome to the NAO. Basically, the cold air gets sent into the SE, and it can't escape out to see due to the Atlantic block. It gets trapped. I have no idea if that is right...just so counter to what we normally look at. BUT, if that is really, that is an ice storm setup if I have ever seen one. Like I said...crazy 12z runs. The interesting question. Is modeling still playing catchup?

The 12z Euro is about to send it late in that run....

Amplified patterns with an NAO and cold…definitely worth watching.

Well, the Tenn sub-forum wins the internet today. You all did good, Flash! Cute as a button. So, if flash is up watching the 0z runs…we know Flash is on the midnight baby shift!!!!

If the cold air mass for Dec 28-Jan 1 verifies, ensembles across the board missed that cold air mass outside of day 7. To me it looks like another one is right after that(roughly Jan 6-7). As John noted, the late December cold snap looks like a dry frontal passage. I would guess higher elevations probably see some upslope if the CMC is correct. It would make sense that the atmosphere would wring out some moisture. One thing in weather, we are rarely going to get perfect placement of every feature on the map. What we want is the feature(which is in our favor) to be the driver. Outside of climatology Jan10-Feb10, it really doesn't want to snow at lower elevations in the Upper South. The base pattern is rain. So, we generally need a little bit of help outside of that window. As is, the pattern in the weeks 2-4 is likely going to have some cold shots, and some warmups. Timing and intensity of any longterm cold snap when/if it returns is TBD. That is why we are tracking what happens after the cold shot to end this year and begin the new one. My guess...models are handling the NAO poorly (duration, intensity, placement). That has occurred more times than I can count. As LC noted, it makes it difficult for models and forecasters to get a handle on things. That is creating wild swings in modeling. It does make sense that at some point, things line-up just enough to send a lot of cold air into the east at some point during January. But really, that is a pretty easy call - it is our coldest month! LOL.

And honestly, after like 20ish days of BN temps....we were long overdue for some warmer weather. I kind of roll with LC. I don't think the MJO is actually having an impact right now...just a really washed out and conflicting signal. I think Nina climatology is driving this. The trough should pull back west for part of the winter due to Nina climatology alone. Then, as the pattern relaxes at some point in January, it may all rush eastward. Very, very complicated pattern in the week 2-4 timeframe right now. The duration and strength of the NAO is likely key. The good thing is that we now know that model feedback has caused two pretty significant errors this winter in the week 2-4 range. As one met noted in another thread yesterday, when models start flipping back and forth....can't really trust that until it settles down. The potential NAO and HL has upended things. We are really one good cutter or coastal from having a pretty massive cold air mass slide all the way to New Orleans. I think we will have a better idea by around Christmas time...

Cutters would help. Where the Aleutian sets up shop as I noted yesterday is what matters. Lots of noted uncertainty ahead. That is what make the hobby both challenging and fun.

The Euro Weeklies control...the majority of that is Jan 10-11. IF that trough slides east due to the NAO, there is a window for strong amplification which we talked about earlier. Just a control run...so TIFWIW. At least two runs in a row of cold temps. If that cold in Canada can ever make its way to the Gulf....sparks are gonna fly IMHO.