Carvers Gap

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.

Yep. Get rid of that feedback over the Pac NW, the vortices kick eastward, and deepen. For whatever reason, models are having a very difficult time (past 5-6 weeks) with infinite vortices over the West Coast. That error is rendering modeling almost useless after hour 200...not that it is super accurate after that during normal times. @John1122got me into watching Mammoth's snow cams during winter. I follow a bunch of their pages after the Carver Gap family visit over the summer. That place is beautiful at all times of the year. Anyway, they are stuck under that western ridge.

I think as soon as a model spins up a low over the Canadian Rockies, sends it SW to where is spins off the CA Coast until it strengthens anomalously, and then dies out...has to be tossed right at the point. The 18z GFS makes a lot of sense until it does that at 210. Those solutions haven't been materializing. When the feedback occurs, it spins up a deep trough in the eastern Pac(which originates in Canada!) and that deepens the AN heights over the EC and ensuing Chinook. Those western Canadian coastal lows are going to get kicked eastward - just how it goes in real life "most" of the time. I think that problem is over cooking the ensembles.

The 18z GFS does indeed find a Christmas Eve cold front. Chinook-then-cold front pattern in place. I actually don't mind that. That is a far better option than the standing ridge(which had rain into almost the Hudson Bay). It will be interesting to see if it intensifies that 24th cold front with time. Originally, it had an anafront on that day. Of course, it has also had sever as well! LOL

Great observations. I appreciate your input as always!

For whatever reason, deterministic global models are having a very difficult time seeing cold fronts in the d10-15 range. I think that is feedback(infinite loop stuff). The chinook looks plausible and is a pretty normal phenomenon in my book. The cold fronts pushing it back make a lot of sense as well. I doubt that pattern is very stable as it requires a lot of amplification to sustain that type of back and forth. I just read LC's writeup from last night. He is firm with his last 1/3 of January and most of Feb being cold. To me that is a 95-96 type of analog. But it fights winters which return with some fight - lots of analogs for those. If the QBO wasn't negative, I would be more solemn. I suspect we see the NAO fire, and as we know, the lead time on the NAO firing is very short.

There is also a part of me that wonders if modeling might not actually correct until inside of d10. The December 20th cold front is fierce as modeled by the 18z GFS. It has steadily gotten colder with each run. I think the time frame monitor after that is the 22-23rd, and then maybe another right after Christmas -a back and forth pattern. Ensembles still haven't caught up regarding the 20th likelihood.

I don’t worry to much about that really. This warmup almost certainly is going have some cold shots embedded. If it keeps eroding, it may become a base cold pattern with warmups. LOL

Really, early December is not snowy IMBY. Sometimes, yes. I have sat through many Christmas parades without barely needing a coat. Normally, the last of my leaves haven’t fallen until late December - that tree drives me nuts. All of my leaves have fallen this year. To be clear, we actually aren’t in the chinook pattern - yet. Let’s see how much of that materializes. The GFS will sometimes lead the way(albeit too quickly sometimes) in finding more cold. Again, we have been dealing with model feedback errors IMHO and still are. I think some type of warmup is nearly certain. I mean it has to warm up, right? I have been BN almost every day this month. Again, I need a few warm days.

We need ensembles of flip…at least one.

The 12z GFS is exhibit A in what happens when the trough doesn’t feedback over the NW.

The GFS has had a sensitive habit of being able to identify cold before other models. It is absolutely lit at 12z.

The 12z GFS again almost wipes out the weeks long AN temps regime. For portions of E TN, we are normal to below for the last ten days of the run!

Dabbling a bit w/ models this morning, the 6z GFS comes pretty close to erasing the standing ridge at the surface. One cold front after another. The Euro and CMC are less enthused, but as we've seen, that can change. The interesting thing this AM is a the TPV paying a visit to New England, and we get a backdoor cold front from it. That has been on several model runs. Been a while since we have seen an air mass strong enough to seep down the western slopes of the Apps(from the East).

I mean this is wild. That is a 5 day map. PNA ridge. EPO ridge. Alaska block. Low east of Hawaii. That is a snowstorm setup. Yes, it is a deterministic run at 300+ AND ensembles have yet to flip....but that is quite the opposite of what has been shown for the past few days. When I see an ensemble finally flip(and they will take some time if they are going to do it), then we know feedback(infinite loops) were at fault here. Let's see if the trend(which began a couple of days ago) ends with a decent pattern. No promises, but fun and interesting to track. Are models finally starting to feel the MJO? Maybe.

And a nice little inland runner snowstorm where that chinook influenced SER has been forecast to pop. I may be in the minority, but I really don't see the warm-up as a phase 6 SER. It is more like a chinook getting pumped by feedback over the NW. Get those lows moving more progressively, and the chinook dissipates as they pass to the east.

We have below zero wind chills in the middle of the warm-up. If that is the warm-up, I would sure hate to see what a cold snap would look like in January w/ that cold air mass parked in Canada.

And as we see the feedback over the NW resolved....modeling begins to look like an MJO on the left side of the plot. Those constant spinning vortices are replaced by more reasonable solutions. That allows multiple cold fronts to march eastward. I don't think it will be wall-to-wall cold like the first 15 days of December, but we could end with a back and forth pattern which is more amplified.

RIP to the southern standing wave on the 18z GFS. We hardly every knew ye.

Here is an article about atmospheric river events. During the 2022-2-2023 La Nina, California experienced nine atmospheric river events. Mammoth got absolutely buried with snow. I thought for sure ARs were Nino driven, but new research suggests it actually has less connection than I thought. An atmospheric river event can actually overwhelm either ENSO signal regardless. https://scripps.ucsd.edu/news/atmospheric-rivers-explain-atypical-el-nino-and-la-nina-years

Middle and Western forum areas definitely do better with a good PAC. The Atlantic helps us with inland runners. We can also do well with a good PAC in NE TN…but many good winters IMBY have good NAO setups, even if briefly. In some ways, TRI scores when DC does.

Definitely good trends here. If the Pac is gonna be taking its time getting its act together, we can try the Atlantic. With the QBO negative and the SSW, a strong NAO is possible and even likely. Keep in mind that -NAOs are often not forecast well in advance. They can upend LR modeling in a New York minute.