Carvers Gap

So, who wants to talk about the 0z GFS-para?

Hey, got two dustings today alone. My house had nothing during one of those, and drove two miles to find the rooftops covered. Made me think of Lake Effect snow bands.... Please read my post in a SNL Jack Handy voice...

The 12K is just a nasty mess.

18z GEFS mean is stout....

With the NAM now coming in line, looks like most modeling is now showing a total mess for the NE Valley and potential well SE of that - even southeast of TYS. Yesterday, I kind of cast a wary eye towards such a quick flip...but it is freakin' cold out there right now. Wind chills here are in the mid to upper teens. I know we are supposed to hit the 40s tomorrow...but this is fresh, cold air...not the stagnant stuff that usually sets up most ice storms. Cold air can definitely get moved around quickly - not saying that. I have seen very cold air masses evacuated within an hour. However, as flat as this storm is trending, it may weaken the warm nose or even blunt it. It would not surprise me to see northern sections of the valley(SW VA) stay frozen most of the way with this. The flatter it gets, the more it behaves as a slider along the KY/TN/VA borders. Models since yesterday morning have signaled frozen precip, and increasingly so. Still not a ton of consistency with amounts, and I don't expect that to change. Right now, looks like sloppiest city!

So, go check out the MJO stuff this morning. The EURO and GEFS are now both doing exactly what the EMON showed a few days ago....headfake to warm phases and then quickly heading towards colder phases. I have noted many times that actual modeling in MJO areas looks like phases 1-2 will fire and that the MJO "should" loop to cooler phases just based on the modeling themselves and not the plots. Will post the EMON with my other account.

Interesting feature on the 0z RGEM (which the 18z NAM had) was a secondary wave showing up along the front. Not implausible, and something to watch. The 0z RGEM is just as nasty as its 18z counterpart, BUT it has about 1/3 less overall precip. I think this is because the system is being forced to slide along a bit vs just roaring up the valley. This fits a recent trend(will it continue) of the SLP being forced further east and less of its energy not being allowed to force its way up west of the Apps. Looks like modeling is feeling the cold high to the north and west of the eastern valley on this run.

The 0z RGEM is yet again flatter and colder than its previous run.

From the MRX evening disco...Time to put the bat signal up for @Math/Met. Good set-up? The aforementioned S Plains mid/upper shortwave will eject ENE across the MS Valley into the TN and OH Valleys during this period while becoming slightly negatively tilted. This along with a 150+ kt upper jet will deepen the surface low as it lifts through the vicinity of the Appalachians and eastern OH Valley. Forcing from the strong upper jet will lead to a strong, southerly low-level jet Wed night that will pump strong moisture transport into the S Appalachians region. This strong moisture transport, isentropic upglide, and additional dynamic forcing as the surface low approaches will lead to widespread precip developing north of an advancing warm front Wed night. Deterministic and ensemble guidance still differ regarding the exact track of the low and resultant thermal fields (as is usually the case in the winter), so precip type at the onset Wed night is low confidence. The GFS is the coldest solution, the NAM is the warmest, and the GEFS/Euro/CMC ensemble means are in the middle. Leaned heavily on the ensemble means and NBM for temps and precip type Wed night into Thurs morning which suggests a period of snow, sleet, and freezing rain possible from the Plateau through the N Valley into SW VA, so generally N of I-40 and W of I-81. Forecast soundings support this idea with a gradually descending warm nose as the warm front lifts N, but as mentioned, precip type and location confidence is low. This will be fine tuned as new guidance arrives over the next 48 hours. One thing that is certain is that a high end mountain wave will occur across the E TN mountains and foothills Wed night through Thurs morning since the low-level jet will be favorably oriented perpendicular to the terrain, it will be a very strong low-level jet of 60-80 kts, and an inversion will be in place below 850 mb leading to ducting values over 20. This will likely lead to 80+ mph gusts downsloping into the foothills such as Camp Creek. As the mid/upper shortwave and surface low lift NE Thurs, a strong cold front will cross the region. We could see a dry slot part of the morning, but expect precip to quickly return as the strong upper jet maintains strong frontogenetic forcing ahead of the cold front with continued strong low-level moisture transport ahead of the boundary. PWATS will be above the 90th percentile with some elevated instability, so periods of heavy rain are possible. Warmer air advecting in ahead of the front will allow any mixed precip in northern areas Thurs morning to quickly change to rain for the afternoon.

I guess hypothetically it could allow for the cold to feed into your area longer. I do wonder if the reason we are seeing modeling in the east change to a mixed bag at onset Thursday is due to: 1. This current system seems a little quicker than modeled, and has changed spacing between it and the second system. 2. The snow on the ground to my west is allowing the cold to work eastward more easily. Tough to say though on a microscale how much of a difference it makes. On a large scale, a nice snowpack can definitely speed a supply or resupply of cold. Keep us updated. Will be an interesting test. I do wonder if the second system is a bit flatter on modeling today due to HP being able to "push" a bit more. We will see if those trends hold.

Really enjoy reading this thread. Great to see so many folks in our middle and western areas getting some winter! Stay warm and stay safe. Keep sharing those pics.

From MRX's Hazardous Wx Outlook just so folks don't thing we are cooking up something unsubstantiated in regards to model support. It could trend better or it could trend worse, but I feel like this is a good description.... An intense storm system will affect the region Wednesday night and Thursday. Strong southerly winds will affect the East Tennessee mountains and foothills Wednesday night and Thursday morning. Precipitation could start as a mix of snow, sleet, and freezing rain Wednesday night into early Thursday morning across parts of the Plateau, northern Tennessee Valley, and southwest Virginia before changing to all rain. Periods of heavy rainfall Thursday may cause some localized flooding. Rain will change to light snow Thursday night with light accumulations possible.

The 18z GEFS mean is roughly 2-6" of snow from SE TN to NE TN and increasing as you go NE. Just have to run accumulations through Saturday in order to pick-up wrap around snow as well.

Man...the 18z RGEM ice total. Man.

I think the NAM is just amped....only model showing that up to this point. As for the 18z RGEM and the 1" of ice for MBY....

Thanks. That is a really good look. Man...don't know whether to trust this suite of models or not, but that is three straight model suite(0z, 6z, and 12z) which have trended towards that solution. My guess is that it would trend back NW at some point. That said, if it trends one more time...money. Two more times...Atlanta.

I thought the same thing. Thing is, the 12a Euro looks like the 12z GFS which looks like the 12z CMC which looks a lot like the 12z RGEM. The whole suite is a giant set-up!!!! LOL.

What is that Kentucky? Also, did the thermals bust or did it just speed up?

Yep. And the comparison loop(just too big to load...Holston???) of the surface pressure locations is much less warm nose and has a tendency to slide and then turn up the coast in the coastal plain. Really jumps on that first batch of precip and gets it out in front of the low.

Let me dig out my CG2 account...will give you all some still shots.

Euro is coming in HOT! (well cold!)

Wow. That is madness. Be sure to post some pics!

12 RGEM is again a messy onset but more so for NE TN this run with .43 ZR in Sullivan Thursday morning. Looks like the RGEM is seeing the warm nose a bit better this run. Powell was asking about the difference. Ya'll check out the temps Wednesday AM over E TN without snow. I had to look twice. Those temps are going to set the stage for really cold rain or a mess Thursday night in eastern sections.

Regarding Weds night/TR the 6z GFS is a total mess...even messier than 0z. RGEM is right there with it. Agree with John on believability stuff. That said, cold bleeding into the eastern valley and getting trapped is a legit option. Whether it happens, anyone's guess at this point. However, the 0z and 6z suites have some significant icing and snow for parts of E TN which did not for yesterday's model runs. Again, the 6z GFS doubled down on its 0z run. Worth a mention...may or may not happen, but a big change. We will see where it goes.

NE TN , SE KY, and SW VA folks might want to get a look at the 0z CMC, 0z RGEM, 0z GFS, and 0z Euro(trend on that one). Worth a look. Won’t add more unless the trend holds - might be a hiccup. 0z RGEM was snow for most of E TN. Colder.