Carvers Gap

I don’t have a ton of time, but good trends at 12z across modeling. The 12z GEPS has a much stronger eastern trough before dumping it west in the last few frames of fantasy land. If we take the idea that modeling trends west with storms….not a bad place to be right now.

The 12z GFS and GEM....now, that is a much better way to start a suite. Very, very close to being something good. I would think models are getting a handle on that EPO ridge now. Plenty to digest with those two.

Just sifting through teleconnections this morning, the 6z GFS deterministic run is the only model(that I can find) which goes positive with the EPO on the 12th. All other modeling turns the EPO negative - ensembles, AI, determinstics. Could the GFS be right? Certainly. But I have some serious doubts. The real question in my mind which has to be answered(and really cannot be yet) is whether that EPO ridge continues to retrograde into Asia, and whether another subsequent EPO ridge then takes its place. I tend to think it continues to retrograde, but then another EPO ridge reforms as the pattern continues to retrograde even more. That second EPO ridge, in my mind, delivers the worst of the cold per winter toward the end of Jan and beginning of Feb. That does not mean I don't think we see chances w/ the first EPO ridge...I just don't think those details are not worked out in modeling w/ so much being juggled and with us still being about ten days out. It is still entirely possible(probable) that the first EPO ridge sticks, modeling adjusts, and locks in that ridge for 3-4 weeks. I just think a back and forth pattern is more likely as that has been the pattern all winter.

Looking at the CFSv2 LR model this morning, it does indeed keep retrograding the 500 ridge into Asia. It retrogrades the eastern trough into the Mountain West....and then it retrogrades yet another ridge into the West and holds it. If that happens, Larry Cosgrove is going to score the coup, and kudos to him for a great seasonal forecast if it does. He has adamantly held that the end of January and early February will hold the worst of winter, and cautioned patience. I think the ridge getting knocked down out west, reforming....wash, rinse, repeat...is the likely pattern beginning on the 12th. One could make a pretty good case that began on Dec 29th. I think at least one of those cycles will have very cold air in the pattern. A lot of decent winters featured that pattern. Let's see if that is how it unfolds. Either way, this winter has been one of wild swings...I fully expect that to continue.

The good thing about mid January is that AN Canadian air masses often verify as BN or seasonal here. Watch as the air moves south…it often flips to BN. Of note, I didn’t think the surface maps looked terrible at all at this range. The real risk is if the EPO ridge at 500 continues to retrograde and the upcoming trough retrogrades after the 20th…leaving us with only a 7-10 day window. The GEPS ensemble at 0z shows that risk at 300. We need that retrograding pattern to pause or slow once in the right spot. Nina winters really want to put the trough in the Mountain West after January. I am gonna give things a few runs to shake out in terms of whether cold fills the trough or not. If the trough forms and the EPO holds, then cold is less of a concern for me. So with the “what could go wrong” out of the way first. Here are some things to consider. The EPS and Euro at range have struggled to see cold this winter…but generally have been good at 500 - but not infallible. That last comment is generally true for most models not named the Canadian. I have simply stopped using the GFS…It flip flops every run (or every other run) and has too many biases to account for. I like the GEM, but must account for its cold bias. The GFS is going to have to show some skill before I use it past day5. I will discuss its solutions, but it has been bad. As for AI, the jury is still out. The AIFS Euro and ensemble have had some rigor. They look good for the upcoming pattern reshuffle, but they aren’t remarkable in their scoring in my book. The AI GEFS ensemble - I don’t trust it but it looks good. So overall, let’s get this potential pattern inside of day 5. The EPO ridge setting up shop has sped up just a hair overnight. I think the EPO ridge forming is about 48 hours from locking-in as “real” on modeling. It is about 5-6 days out. Once inside of d5, I will “buy” that feature, and that goes for the rest of the features in the map. Until it sets up, I don’t think we are going to really know if the trough fills with cold, if the NAO bridges over, or if the EPO ridge holds long enough to be a force. That is a lot to juggle. I would guess (and could be wrong) that once the EPO forms that cold will fill the eastern trough IF the EPO ridge holds and doesn’t continue retrograding to Asia.

After seeing the Sierra Nevada this summer and seeing the deep snows from forecasts and webcams...we started talking about the Donner Party. They got stuck north of Mammoth Lakes and Yosemite National Park in a place just west of Lake Tahoe. I never could understand why they didn't turn back once it started snowing. Once it snows 4-5', you really are stuck without modern machinery or unless a thaw occurs - I understand now why they got stuck. Really, there was nothing east of the Sierra Nevada at the time (to over winter), and other than grass meadows(where Reno is now) there was no place to wait until spring. There "point of no return" might well have been Fort Bridger. Once they crossed the Wasatch, they were committed. If you are interested in the story(and it indeed mentions the MJO of all things!!!), The Indifferent Stars Above is a great book. It is not for the faint of heart due to the subject matter, but...it provides a riveting story which begins in Illinois, covers each section of the trip(from Great Plains to the Sierra) and ends just short of Johnson's Ranch. There is debate on how bad that winter was. Some say it was a low water year. However, the photos of the stumps in that camp were cut nearly 20-25 in the air. It is likely the snow was incredibly deep, but water content low. There were roughly ten winter events that winter, some from atmospheric river episodes. Winter came early that year, and by some reports, even the hills above San Francisco saw snow that fall. Winter, for sure, came early that year. It buried the inexperienced travelers(at least inexperienced in winter camping and survival). What came next is one of the most horrific narratives in the American settling of the West. Amazingly, some of them walked out during the dead of winter. I though most died in that bowl of ice and snow near the summit. Nope, roughly half survived. 2/3 of the men died. Only two single men survived. Larger families survived.

GEFS trends from 0z to 18z. Pretty big moves.

The 12z EPS and GEPS have this as well. AI models can be sketchy for sure - completely unknown. I am not sure they are actually "learning.". I like the EURO AIFS better than the AIGFS(seems not overly rigorous) FWIW. The 18z GEFS continues to trend the rest of the other ensembles w/ the eastern trough. The good thing is the EPO ridge moving into position is almost 7 days out. I will feel a lot more confident once it sets up shop. The NAO has verified as pretty strong...so good sign modeling is handling blocking well. We have definitely tracked patterns which fizzle. Let's hope this isn't one of them. We have also tracked many patterns which eventually verify. Good info on the ENSO and PDO regions - thank you!

The actual EPO is to supposed to build Jan 8-9th. So, that transition is well within ten days. Right now, that ridge building starts at about 180. The transition to that ridge is arueably occurring now.

The 18z AIFS Euro ensemble is pretty much awesome. Big ridge out West, and big trough over the East. Makes sense.

The deterministic GFS over the last four runs has shifted the 500 pattern about 500-1100 miles eastward depending on the feature.

We will see. The GFS is relying on the ridge being over the East and return flow from the Gulf. The trends right now are bit time towards a trough over the East on that model. That model is incrementally caving IMHO. If so, the trend would be much more dry.

The great thing is the 18z GFS seems to have figured out that the trough has to kick out if under an EPO ridge like that. Just wait till 0z, we will have something new! Haha.

The EPO ridge hasn't been delayed as of yet. We lost a couple of cold fronts on the 4th and 8th. This has been moving pretty steadily in time. But we all obviously know the rules. Most of the folks here are pretty solid veterans when it comes to flip flops.