Carvers Gap

Just looking at northern hemispheres modeling, the coldest air on the planet will likely be over the Yukon d8-15 roughly. The mechanism to deliver that into the Upper South is present in the forum of a flat western ridge. The colder of the air (for now) will slide across the upper MidWest and into the NE. HOWEVER, any kind of cutter or storm which gains latitude could send all of that into the Tenn Valley region. Both the 6z GFS and 12z Euro have minor slp events which do it. I cannot imagine what a big storm would wrap in. A portion of the TPV is basically parked over the Hudson Bay, and just pinwheels cold air southward. In other words, we have a trough modeled. The source region for that trough is very cold air. Remember these winters where NA was void of BN air...not this year!

The 12z GEFS has temps twenty-five degrees below normal in WI at 195 w/ all of that headed SE. During that same hour, our forum area has departures of fifteen degrees BN. That is frigid for an ensemble at this range. The 12z GEPS is even colder over our forum area w/ temps 20 degrees BN over much of the area. The GEPS brings another cold shot around the 21st. The 12z EPS is rolling. It has the same cold shot, and is a bit "warmer." It is only 10-15 degrees BN. That is cold for a model w/ a bit of a warm bias in d10-15. Short story, even at this range, there is a growing likelihood of very cold air making it to our latitude by mid-month. Both the GEPS and AIFS ensemble(to some extent), show the second cold shot around the 20th. With so much snowpack immediately to our north, these cold air masses are on greased skids.

The 12z Euro is frigid w/ a couple of days of real feels that have below zero readings. Both the 12z GEFS and GEPS ensembles show cold temps some time between Dec 14-17th. I suspect we see an anafront(a constant them of mine I know) at some point in that time frame. I think we could see 1-2 very cold air masses push through the area mid-month. And honestly, all of us would probably appreciate some moderation if those come to pass.

I think the next "system" will be Sunday night. The 12k NAM has it as does the RGEM. it is coming in at night. If the NAM is correct, that could be minor to moderate upslope for the Plateau and maybe the Apps. The MJO is a "choose your own adventure" this morning at CPC. It has yet to loop back around. But....the GFS and Euro now show it stalling in 8 - and I am still not sure that actually happens! If it actually stalls in 8 for a long period of time(and it is already halfway across 8), that would leave the door open for very cold temps. I almost kind of wonder if the CFS has it right. It trucks across the cold phases, rolls through the COD to 6, and then goes back through the cold phases again. That looks an awful lot like those CHI graphics Jax recently posted. Strong 1-2, strong Maritime, continues to dateline. I do think we have a cold shot coming mid month...we'll see if I am right! LOL.

The GFS has had this time frame(give our take a couple of days from Dec 17th) on-and-off as a potential time for very cold air. The 0z Euro also has this but just a bit shallower. The extreme solutions have not verified yet, but only IMHO because climatology really hasn't supported it yet. By mid-December, very cold air has precedent over the valley regions. This also fits recent MJO rotations - I have not looked a today's as of this post. Again, if you like nickel and dime events(sometimes w/ mixed precip), the next 2-3 weeks are full of them. Let's see if they verify. Right now the trough axis is slightly too far to the East. Where is the actual SER when you need it, right?

The 6z GFS might be its coldest run yet. The 0z Euro and CMC have several light events which are northern stream driven. Models continue to get colder.

You all are keeping the lights on which we appreciate greatly!!!!

I haven't talked a ton about the d10-15 today, but modeling is MUCH colder with it. The 18z GFS is frigid. Its ensemble isn't much warmer. The EPS at 12 was cold. I think the MJO juice has made it to the deterministic models and their accompanying ensembles @Daniel Boone! The juice is loose!

Like that profile pic!

I have to think the northern Plateau, SE KY, SW VA, and 1500'+ in NE TN....gonna have a decent little event from this. The cloud cover today has prevented warmer temps from rolling in..

What I see from the 12z GEPS and EPS is very cold air in Canada that keeps pinwheeling into the US old school style. And that setup is a very stable pattern unlike other cold patterns we have seen. JB noted that wave lengths tend to shorten up during phase 8 and wx models will often struggle with details and strength of cold shots. If we kind of assumed this pattern began just after Thanksgiving, it makes sense for it to last to Christmas or just after, then Jan is likely warm, followed by another cold shot. This set-up reminds me a lot of 95-96 in terms of the overall sequence(maybe not the snow). Last winter did as we'll.

The Euro, after stumbling and bumbling for 4-5 days(losing the pattern), has a reasonable transition of the MJO. I think it just keeps rotating around. The GFS/AmericanModeling has tried to loop it around and been wrong with that on multiple occasions. Does it stall? It may. To me, this looks like it will transit cold phases, go COD 3-5, exit into a strong 6, and come right back around. The GEPS and EPS looks decent in the long range. The GEFS keeps pushing back the flip. I do think we see a ridge(maybe???).

Just zooming out a bit from this event...there are a lot of potential small events in the pipeline. The 12z CMC is my "go to" at 12z. Though the 12z GFS is pretty loaded up with opportunities.

URGENT - WINTER WEATHER MESSAGE National Weather Service Morristown TN 1214 PM EST Thu Dec 4 2025 TNZ012>017-035-036-045>047-050500- /O.NEW.KMRX.WW.Y.0011.251205T0000Z-251205T1200Z/ Scott TN-Campbell-Claiborne-Hancock-Hawkins-Sullivan-Morgan- Anderson-Unicoi-Northwest Carter-Southeast Carter- Including the cities of Howard Quarter, Clinton, Smokey Junction, Sandlick, Norma, Slick Rock, Sneedville, Caryville, Mooresburg, Oak Ridge, Big South Fork National, Oneida, Kyles Ford, Bristol TN, Clairfield, Huntsville, Royal Blue, Springdale, Erwin, White Oak, Evanston, Treadway, Arthur, Kingsport, Limestone Cove, Lone Mountain, Elizabethton, High Point, Petros, Harrogate-Shawanee, Jellico, South Holston Dam, La Follette, Unicoi, Elk Valley, Fincastle, Pine Orchard, Elgin, and Hampton 1214 PM EST Thu Dec 4 2025 ...WINTER WEATHER ADVISORY IN EFFECT FROM 7 PM THIS EVENING TO 7 AM EST FRIDAY... * WHAT...Mixed wintry precipitation expected. Total snow accumulations of up to one inch, along with a light glaze of ice. * WHERE...The northern Cumberland plateau and portions of the northern Tennessee valley near the Virginia border. * WHEN...From 7 PM this evening to 7 AM EST Friday. * IMPACTS...Plan on slippery road conditions. The hazardous conditions could impact the Thursday evening and Friday morning commutes.

Once this stuff starts falling, we need a brave soul to post a thread or the "storm." It ain't gonna be me. LOL. The EB looms....

Temps in Kingsport range from 35-39F. It is a lot colder than I expected it to be.

It isn't warm out there. The current HRRR has 1-2" over TRI w/ snow still falling at the end of the run. Both the 12z GFS and Euro have light amounts as well w/ the GFS having more. The NAM is pretty meh over TRI. ***Winter Weather Advisories are posted for northern areas. MRX has seen the 12z suite.***

FWIW, that axis looks about right w/ TRI maybe being a sloppy mess.

With the axis of this narrow strip of snow, small upstream changes create HUGE downstream changes. Think of it like this. When a hurricane is approaching the coast at an angle, any upstream change drastically changes the landfall location. This snow axis fluctuates with almost every run. The current 12z GFS is a good lollipop for TRI. The 14z HRRR is north of its past run and TRI is blank. I think time of day is going to be huge. I think likely that some in the forum area will see a stripe of frozen precip along the northwest boundary of this. Where? Your guess is as good as mine. But a line from Nashville to Abingdon, VA, seems about right. Anyone 30 miles to the south of that and 150 miles north of that is fair game.

Yeah, I don't trust any model at this point. Glad I don't have to put out a product tonight to the public! This is one of those which could bust either way.

Jax, looks like basically a reload. Lots of conflicting signals there. Great share.

This pretty much sums it up...models are all still all over the place. National Weather Service Morristown TN 606 AM EST Thu Dec 4 2025 ...New AVIATION... .KEY MESSAGES... Updated at 601 AM EST Thu Dec 4 2025 Dry weather today before increasing precipitation chances tonight into Friday. - Probabilities for minor impacts from ice and snow are trending upwards across the northern Cumberland plateau, southwest VA and extreme northeast TN for tonight into Friday morning - Very low probability of rainfall this weekend. && .DISCUSSION... Issued at 1240 AM EST Thu Dec 4 2025 Dry today with continued below normal temperatures. Increasing precipitation chances tonight into Friday morning. The good news is that the latest HREF probs mostly align with the previous forecast. The bad news, the last two runs of the HRRR are well above the HREF means in terms of snowfall amounts. This makes for a low confidence forecast. Latest HREF guidance shows probs for at least 0.5 inches across southwest VA are in the 30 to 50% range. Probs for at least 0.5 inches for extreme northeast TN are generally from 50 to 70%. There are also low probs, 10 to 20%, of at least 0.5 inches across the northern Cumberland Plateau and areas along and near the TN/KY state line. Upping the prob amounts to 1 inch yield much lower values, around 30%, but for very isolated locations for both southwest VA and extreme northeast TN. The LREF members shows slightly higher prob values, and with more spatial coverage, for the 0.5 and 1 inch prob values. LREF shows moderate probs of 1 to 2 inches across southwest VA and into extreme northeast TN. The REFS output aligns fairly well with the LREF ensemble probs. Then we have the HRRR. The latest two runs of the HRRR show even higher values than what the REFS and LREF ensembles means suggests. The HRRR wants to paint a solid 2 inches in across the northern Plateau, and 3 to 4 inches in across southwest VA and extreme northeast TN. Because of all this, uncertainty in snowfall amounts is high. These higher end amounts would result in travel impacts while the lower HREF amounts suggest little to no impacts. With this forecast package, have trended snowfall amounts slightly upward, above NBM, based on latest model data and trends. In addition to the snow, NBM also painting in some light icing across these same areas. Please stay tuned to the forecast as the snowfall forecast will likely continue to change given the current variability. Please plan ahead for potential impacts with this system. Areas from Knoxville and south should remain all rain through the event. The bulk of the precip will have ended by Friday afternoon, but a few light showers may linger into the evening hours. NBM still wants to hold on to some slight chance POPs for Saturday and Sunday but it seems warranted so will leave them in the forecast. Rain chances continue into next week as an active pattern will be in place across the country. As of now, Tuesday look like it should be dry though and is most likely to be the nicest day of the forecast period.

The 18z Euro has a light upslope clipper around the 8th....need to keep an eye on that one.

Some nice trends on both the NAM and RGEM if you like frozen. To me, this also bodes well for future systems. It looks like modeling under-did the NW shield of the precip. So this super dry sliders which follow tomorrow night...might have a bit more juice. Good luck on overnight modeling to everyone. I hope someone gets an early season snow!

Let’s see what MRX notes with their next update in regards to soundings.