Carvers Gap

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.

Area Forecast Discussion National Weather Service Morristown TN 154 PM EST Sat Dec 13 2025 ...New DISCUSSION, AVIATION... .KEY MESSAGES... Updated at 1236 PM EST Sat Dec 13 2025 - Light snow accumulations expected across the high terrain of East Tennessee and southwest Virginia overnight into Sunday morning. - Bitter cold will surge into the area for Sunday through Monday morning. Please see the Cold Weather Advisories for additional details. - Warming trend begins Tuesday with above normal temperatures by mid to late week. Conditions will be dry during this time. && .DISCUSSION... Issued at 1236 PM EST Sat Dec 13 2025 A broad upper level trough remains in place over much of the central and eastern CONUS. Shortwave energy translating through the synoptic feature tonight into Sunday will sharpen the troughing as a surface front progresses through the region. Some light ra/sn will occur during the overnight hours as this energy translates through the central and southern Appalachians, however, the greatest probabilities for light snow accumulation will be limited to higher terrain of the East Tennessee mountains and southwest Virginia. Overall, moisture in the DGZ is lacking and better northwest flow does not initiate until the bulk of the moisture is departing the region. Will cover this with an SPS for now, ending it at midnight to allow for the next forecast desk to make any additional considerations. The main concerns will be well below normal temperatures advecting into the region as winds veer NNWly and become gusty behind frontal passage. Temperatures around 20 degrees below normal are largely expected across the region Sunday into Sunday night. A Cold Weather Advisory has been issued for the Cumberland Plateau, southwest Virginia, and our East Tennessee mountain zones starting around sunrise tomorrow morning. The gusty winds and well below normal temperatures will result in wind chill values around zero, to as low as 10 below zero in the highest terrain of the mountains. By late Sunday afternoon, the remainder of the valley locations are introduced to the Advisory as cold air continues to filter into the region. Overnight lows in the low teens to single digits will be widespread. Many valley locations will see wind chills in the single digits to near zero. Cold Weather Advisory products will come to an end shortly after daybreak Monday, when a gradual warming trend is expected into the mid-week as the anomalous troughing ejects northeast and H5 heights slowly recover. For Wednesday night through Friday, the main storm track will be across the northern third of the nation. The fast but more zonal flow will quickly move a series of short-waves with associated frontal boundaries moving across the region. Ensemble cluster analysis shows differences in timing of systems but overall increasing chances of precipitation are expected towards the latter half of the week.

The CFS forecast has been a lot different than any other MJO forecast. Is it an outlier, but also correct?

I really hate having to dig through MJO data - yuck. Anyway, I read the MJO report from the 8th by CPC. So, I think I know how to read the following map. The orange is suppressed convection. Now, it is important to remember there is almost always convection at this time of year over the MC, and I think that is a mistake some(not in this forum!) are making. You can have convection, but it be suppressed IMHO. That simply means less than the norm. I don't "think" phase 8 and phase 5 have a one-size-fits all scale for convection. I would guess the MC has more convection, ie it could still have convection but less than the norm. The enhanced(more than normal) convection is blue...and that is phase 8. It isn't moving. In fact, you can see some convection firing in east Africa which is 1-2. What I want to know on the CHI plot is which color is enhanced and which is suppressed. I need to get that straightened out so that I can compare the two. @jaxjagman

I think modeling has been suffering from really bad feedback(infinite loops). The other thing is that our cold source this season is insanely cold. We have seen years where 500 maps don't match the surface, and this might be one of them again.

The CPC MJO plots, and this is not meant to be contentious, are in phase 8(has never left). They are parked there. Something is gonna have to give...either warm modeling or incorrect/correct MJO plots. Please answer --> Someone remind me...the green is the MJO convection, right? If so, mid Jan could be freaking cold. If green is suppressed convection....

The warm-up has been pushed back past the 20th as most models now see a cold front(another strong one) around the then. Will there be another prior to Christmas and after the 20th? Maybe. This pattern will have some anomalous warm days, but will also have some anomalous cold days. It may average out warmer, but that is not a full on torch on deterministic runs. It seems like each suite is wiping out more warmth. If it were the other way around and I was hoping for a flip to cold...I might be questioning whether it could hold on.....

I really think it has been a while since we have had a cold source like this. Models/people are trying to adjust.

I don't have a lot of time this morning. A trend worth watching...overnight and morning deterministic runs (CMC, Canadian para, 6z AIFS, and 0z Euro) continue to erode the warmup. That doesn't mean we won't see warm air masses, but go look for yourself. They have, even the gfs, found the Dec 20th cold front. This really looks like more of a back-and-forth pattern where warmth surges, cold erodes it quickly due to the cold source, and wash/rinse/repeat. Ensembles aren't there yet, but at this range...they will wash out any trends.

The 18z AIFS is one big HL block at the end of its run. The Euro Weeklies control had a ton of blocking at the end of its run. That sure looks like the fingerprints of an SSW.

I finally just got a cheap Photobucket account. I click host and the photo has a link.

Well, it's Friday. Here is a bonus...Take a look at the run-to-run change when the slp (spinning endlessly off of Cali) doesn't feed back. Then take a look at the actually 500 map. There is the Alaska block, and the same persistent pattern(hard to break) that we have seen for a few weeks. The PNA flips positive. Should be a good run the rest of the way here in fantasy land.

I think most of us are not used to having a decent cold air source. 500 maps can get wonky and sometimes are not represent the surface w/ these. When that happens, it is really important to look at surface pressure. The mechanism(on that run) is in place to send the TPV south. It just got hung up. Still, that is a good run at this range. Cheers. Maybe I will come back for 0z.

That is just a timing issue or that is a huge winter storm. As is, it is CAD city and Virginia gets hammered. The surface high slides a little bit too far ahead. If this were to get over the top, slider city. Very, very close. And just amazing given the torch that has been shown for days for Christmas. This is the GFS' second run w/ Christmas cold. Let's see if it can hold and get this inside of ten days.

If there was no potential feedback over the PNW, all of it would have come out. Oh so close.

Give me this, and we ride at dawn...

18z suite commentary...I will just update this post. 18z GFS: At 162, it looks like it is about to unload some cold air into the Lower 48. The trough in the PNW is less, and the BN heights over northern Canada look to be rotating southward. At 183, this looks like it is gonna send it all???

This is probably a little bit over done, but wow. The 18z GFS puts down 2-3" on Sunday for TRI and the foothills. I would not be surprised to see more areas which see at least some snow in the air - maybe not even seen on radar.

Afternoon disco from MRX... 922 FXUS64 KMRX 121734 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1234 PM EST Fri Dec 12 2025 ...New DISCUSSION, AVIATION... .KEY MESSAGES... Updated at 1232 PM EST Fri Dec 12 2025 - Light snow accumulations possible mainly in the mountains Saturday night into Sunday. - Bitter cold will surge into the area for Sunday into Monday. - Warming trend begins Tuesday. && .DISCUSSION... Issued at 1232 PM EST Fri Dec 12 2025 Tonight into Saturday we will be under the influence of surface high pressure, and high temperatures will be near to slightly above normal for this time of year on Saturday. The brief warmup will quickly be forgotten as a strong cold front surges through our area Saturday night ushering in an arctic air mass for Sunday into Monday. The front will have little moisture to work with, but we will likely see some showers quickly changing over to snow showers and flurries Saturday night as the front moves through, with snow showers and flurries lingering into Sunday especially over the normally favored higher elevation areas as the northwest flow and cold advection continues. Right now, it appears any snow accumulations will be most likely over the higher elevations of the E TN mountains and SW VA as is typical in these scenarios. Current ensemble data suggests a very low chance (around 10-30%) of exceeding one inch of snow even in these favored areas, but think this is underdone at this point and as more hi-res guidance is incorporated these probabilities will likely increase. Even so, any snow accumulations are expected to be light. The bigger story for most folks will be the cold. High temperatures Sunday daytime temperatures will generally be near or below freezing even in valley areas, and the wind will make it feel even colder. Lows Sunday night will be in the single digits and teens, and while it currently appears winds will be on the decline during Sunday night which will suppress what could be even worse wind chills, still wind chill values in the single digits will be common in the valleys with below zero values for the higher mountains at times Sunday night into Monday morning. It is still unclear how much if any of the area will dip into cold weather advisory territory Sunday night into early Monday, but it looks close enough to warrant continued inclusion in the HWO for now. The center of surface high pressure will eventually shift to our east by Tuesday allowing for a gradual warmup to begin, and temperatures will likely be above normal by Thursday. Both Tuesday and Wednesday will be dry, but moisture will begin to increase later in the week. Models are still in poor agreement on exactly when the next chance for precipitation will arrive, but current ensemble data supports having chances for rain back in the forecast by Thursday.

MRX graphic from social media. Feel free to post your local.