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Carvers Gap

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  1. Carvers Gap
    ARW is in as well. Crazy stuff. I have my doubts that feedback is going on....but big totals like that are not unusual for a Feb snowstorm. Models often underestimate QPF. Wild.
  2. Carvers Gap
    I know, right. The SE trend has been real all winter, but I hadn't even bothered to check the near term. Looks like it is rates driven w/ some marginal cold to work with.
  3. Carvers Gap
    Yeah, it snuck-up on me for sure. I was just looking at the GFS trends, and it has moved SE for several runs. When I say "on time," the 14th was the original pattern change date. Crazy that west TN(maybe portions of middle) might be backing into a storm.
  4. Carvers Gap
  5. Carvers Gap
    Memphis w/ the afternoon disco....sorry, western forum folks, for skipping this! You all might have something to track. The aforementioned upper low is forecast to move directly over the Mid-South on Monday. As this occurs, wraparound precipitation will likely impact portions of northeast Arkansas and west Tennessee. Some guidance is beginning to hint at potential sleet / snow development on Monday for these areas. A few snow flurries may be possible as forecast soundings depict below freezing temperatures throughout the majority of the atmospheric column. However, surface temperatures will likely be a few degrees above freezing so anything that does fall should melt quickly. The greater concern on Monday will be winds as the center of low pressure moves overhead. Currently, guidance keeps winds just below Wind Advisory criteria. However, would not be surprised if this headline is needed in the coming days.
  6. Carvers Gap
    Wow. Check out the 18z HRRR....it has it as well. Right on time if real!!!
  7. Carvers Gap
    Yep, that is it. That is going to be a major loss. Thanks for the clarification. How long until that occurs?
  8. Carvers Gap
    The 12z EPS looks like it caved to the GEFS in the long range. As Jeff noted the MJO is going into warm phases on satellite and the previous convection over the MC didn't moved into the eastern Pac as modeled. On to bowling season. Storm track is still favorable, though cold sources are not. Of note, Asia often gets first choice when it comes to SSW events. The cold has dumped there. Our cold sources are also not great right now. Even if we had a perfect HL blocking set-up, there is no severe cold(in Canada...though Canadian cold is still cold here in TN) in medium and LR modeling to deliver. Eastern NA is often third choice when it comes to strat splits. Now, the current strat split...that is TBD. The current cold in Asia is due to a Jan SSW. So, a very cold spell during March can't be ruled out once this SSW runs it course - 2-3 weeks later would be probably impacts to mid-laititudes. All of that said, it was super common during my youth to see severe cold delivered into the TN Valley, and then winter would be over after that at lower elevations. 84-85, 89-90, 22-23, and maybe 17-18 (could be 18-19) come to mind. 09-10 and 14-15 were more prolonged, but that is a rarity for most of the winters I lived through. Usually, winter showed-up, hammered us, and then left. I still think LR modeling is probably washing out a cold shot. You could see the 12z GFS try to deliver the goods late in its run. When wave lengths shorten during spring, modeling will often miss very cold air masses that are quick hitters. I should note that the 12z Euro control looked super similar to the 12z GFS. That could/would likely deliver some very cold air w/ that set-up. Is the EPS being discontinued? That is the word on the street...maybe above towards a control oriented model suite?
  9. Carvers Gap
    The 12z CMC definitely shows the potential for the trailing system around the 20th.
  10. Carvers Gap
    The 12z GFS was very cold and is well out of sync with its ensemble. Could we be seeing modeling beginning to sense blocking? Maybe. This occurred in early January(when modeling missed the mid-Jan cold shot), and that isn't the first recent GFS run where the TPV got trapped. I suspect that there is one really cold shot embedded in the pattern between the 20th-30th.
  11. Carvers Gap
    Meanwhile, the 12z Euro does have some talking points. The 17th system is more of a slider as confluence is helping there from the NAO block. North of I-40 is light snow. There is another system right on its heels.
  12. Carvers Gap
    Here is a great article about the NAO. It does a great job into really looking at all sides. Be sure to read the part in conclusions about correlations to snowfall along the East Coast. That could also be read as areas just inland from the coast as well such as E TN - but I am extrapolating. But overall, it covers a ton of great material, and is not one sided. Kocin is mentioned in this. I will try to get some of his stuff later. https://wcd.copernicus.org/preprints/wcd-2020-20/wcd-2020-20.pdf
  13. Carvers Gap
    The big thing to watch with NAO climatology, the better storms IMO often occur towards the end of the NAO cycle. We have definitely had more -NAOs during the past 4-5 winters. 2-3 years ago it became more apparent that we were headed back towards a -NAO winter scheme. We really had gone maybe a couple of decades without seeing consistent winter-after-winter -NAO stuff. (Now, that is off the top of my head.) So, it is important to really dig into storms versus actually seasonal or month by month analogs. NE TN can score from a DC pattern that is snowy. We can also score from an EPO pattern. Where we have trouble scoring is with a moderate to strong ENSO of either type. We need ENSO forcing to be weak but not nada either. As for middle TN during the past three years, I could make more of a case for La Niña driving those patterns as you all often need a bit of a SER to score. It sucks in E TN, but that SER often produces a storm track along the Apps or through the eastern Valley. Whether that SER is a product of an EPO or the EPO is the product of the SER...now that is a fun debate. Why? Well, the SER is basically a standing wave and maybe we could also call it a block. When that SER sharpens along the SE region it backs flow again much like the NAO, and it consequently (one could argue) buckles the jet. I will have to go back and look, but one of the big recent storms for middle TN or the ice storm had a stout SER which maybe was connected to the NAO. It seems like one of those storms came directly at the end of NAO blocking or at the beginning. I am not in a place where I can check NAOs currently. Either way, when the Atlantic has a block form (SER or NAO), that often forces the upstream ridge to pop. Placement of the mid-continent trough is highly dependent on where the block sets up shop. And it makes a big difference here. Now, prior to these recent current -NAO winter episodes, the Pacific often drove the pattern as the NAO was absent. However, that was not what my original post which was about re: whether the EPO drove this recent January outbreak. The EPO during this recent outbreak was a likely by-product of the NAO. So rule of thumb. Some EPO pattens are a direct result of NAO blocking, but not all EPO patterns are a result of NAO blocking. When a couplet of NAO and western blocks form...pretty good chance the NAO forced that.
  14. Carvers Gap
    This is the current run at 12z. Look at the NAO region. It is (edit)weaker than four days ago. Notice the upstream (upside down) omega with the trough is not sharp compared to four days ago(below). The western PNA is great, but without the Atlantic block...nada. This was just four days ago. Notice the NAO region(Greenland) is marginally better as the heights are higher over a larger area of the Davis Straits. The omega contains the BN heights which is carved out better. Notice the storm is sharper and a better cold air supply. Look at the difference on the surface. Boom. The NAO below has actually backed the flow just enough that the PNA ridge is in EPO territory. This is what I am talking about when I say "NAO driven." That western ridge buckles so that it is a bit more in the eastern Pac. The NAO forced that IMHO. Without the stronger NAO, the ridge on todays run (above) pushes slightly eastward (in the West), and we lose confluence and our cold air supply to boot.
  15. Carvers Gap
    And even with this system on 17th-20th(it has moved around a bit), if one goes to Tropical Tidbits at 500, all one has to do is toggle back until they see the heights over Greenland get stronger. I think those runs are around Feb 7th at 6z(off the top of my head...I breezed through that a minute ago). Then, go look at the surface for that storm. As the NAO has weakened during subsequent runs, the storm has gotten warmer (until 6z today which was a good run). One thing the NAO block also does is it also often turns the AO negative, not always but often. That opens the door for cross polar flow from Siberia. The NAO block then often forces that flow into the East - if it doesn't hook into the SER! LOL.
  16. Carvers Gap
    Modeling was likely in error about the upcoming NAO intensity which was forecast to be stronger than it is now for the second half of February. As the NAO diminished...the ensuing runs have warmed dramatically. But one thing I tend to note, modeling will often struggle with HL blocking up until the last minute. My guess is the QBO has reversing or is about to...that is correlated to negative NAOs as well. I haven’t looked at it recently, but it is due to flip. The NAO might be one of the most difficult things for current computer modeling to effectively portray. But let’s see where the pattern goes after the potential system on the 18th. My guess is base warm(with cold interludes), but I am not completely sold on that.
  17. Carvers Gap
    The other driver during that January timeframe was the MJO relented and rolled into phases 1-2-3. It wasn’t overly favorable, but it wasn’t hostile either. For an induced NAO block to form a ridge out West, the Pacfic jet extension had to move westward. As soon as that jet extension relented, the NAO buckled the flow. This time around, not sure that is going to happen as the IO and MC are muddying the MJO waters. The NAO doesn’t play nicely at all times. Sometimes it hooks into an eastern ridge, and sometimes it can’t overcome a jet pounding the West Coast. But...it is a common ingredient in many, many great EC and E TN storms, and it was this past January. For now, it looks as if we have potential for a storm on the 18th...might be our last shot.
  18. Carvers Gap
    The downstream NAO ridge/block often forces the western ridge to pop by buckling the jet, and that is likely what occurred during January. Without the NAO, the flow would have been zonal. The NAO sharpens western ridges(forces the upstream jet to buckle) and brings cold southward but allows storms to gain latitude along the EC. The debate for me is not whether the the EPO was there, I just don’t think it would have been there without the NAO buckling and forcing the trough into the East. That trough in the East forced the western ridge to pop. I just don’t think the January pattern was EPO driven....the EPO was a byproduct of downstream blocking and a retraction of the Pacific jet. Without the NAO, the EPO ridge doesn’t form in a meaningful way IMHO. That is my point. As soon as the NAO disappears, the forcing for the EPO is lost...and it disappears almost immediately. This has been a common then during the past 4-5 winters. The cold during the past few winters has often been coupled with a brief NAO episode. Think of it like a water hose on high pressure. When the end is blocked, the hose will often buckle. That is exactly my point. Without the block - no upstream EPO block this winter. We can get into previous winters and storms later, my original comment was specifically about the January cold being driven by the NAO block, and it was. I stand by that comment 100%. You will find that is often a common theme during big EC storms. And that has to be fished out of data (almost on a day by day basis) as the NAO (of late) appears for 2-3 weeks and won’t show in a monthly 500 pattern on reanalysis as it gets washed out. Again, what the NAO does is it forces the jet to buckle in an upside down omega pattern and forces confluence over the eastern half of the country. E TN, more often than not, needs it. That’s what I have, the defense rests.
  19. Carvers Gap
    I will add some scientific journal articles about the NAO itself. Its influence on EC wx/climatology is well documented and well studied. But again, the 6z GFS has hopefully a trend towards a colder Feb 18 system.
  20. Carvers Gap
    You all can dig up my old NAO posts. It is a key driver for E TN snowstorms. There isn’t a ton of debate on that. It is also a key driver in many Kocin storms. For middle and west TN, the EPO is more important as those areas just don’t benefit very often from coastals. -NAO has driven many snow storms during the past 4-5 years. It produces confluence. Without it, everything races out to sea. When we lost the NAO during late Jan, we torched. This is key...The NAO will often force the Western ridge to form as the upstream NAO ridge backs flow, forcing a trough over the East, and forces an almost upside down omega by buckling the jet northward as it crosses the West coast. Without the block over Greenland, the upstream ridge will often not form over the eastern PAC. It buckles the jet. Without the NAO, the jet doesn’t buckle this winter. That is just atmospheric physics. January’s pattern was NAO driven as it forced the upstream jet to buckle. And I do have the saved maps for that sequence and also many other recent storms - whenever I ran out of memory on Am Wx...I moved my graphics to cloud based servers. Because E TN is closer to the Atlantic, it makes sense that the Atlantic is our main driver. When I get time, probably over the summer as I am getting next winter’s forecast ready, I will pull some analytics. (Now, we haven’t talked about a PNA which is different.). I will take individual storms and look at those. Seasonal readings don’t tell the story. They have to be system by system. Often NAOs won’t last the entire season. They can sometimes be brief. What the NAI does is buckle the jet. That backs up flow and will often force or sharpen the ridge over the eastern PAC. Plenty of evidence of that in many great eastern snow storms.
  21. Carvers Gap
    The beginning of March is within the window that we have been talking about since mid Jan. Glad he is discussing that.
  22. Carvers Gap
    We just need the Pacific not to have massive jet extensions....that has been a problem for several winters. I have my theories on why this is occurring(one of you knows my thoughts), but I do wonder.
  23. Carvers Gap
    Modeling was completely blind to the mid-January even until just days prior. Big storm wen through the Plains and modeling flipped. I think we are going to have to get this system worked out on the 18th, before we know for sure the hand we are dealt. I honestly don't buy the EPO stuff this winter. We got a decent rotation of the MJO and the NAO fired. It got cold as the NAO pattern matured. The EPO helped some, but without that NAO, the cold wouldn't have been there at all. Same was true last winter. The reason we have seen severe cold during the last 4-5 winters is the NAO is beginning to fire again. We went a couple of decades without a true NAO negative trend. In E TN especially, the EPO is not always a driver. The storm that brought snow to this area just three weeks ago was driven there by the NAO block. The EPO would have not allowed for confluence. E TN almost always does better for snow w/ an NAO block, and that was true this winter w/ Knoxville seeing that record snowfall.
  24. Carvers Gap
    Right now it is the GEFS vs EPS/GEPS....there is not consensus that a warm-up is permanent. It may well be the reality, but that is not the case right now. Pretty substantial model war under way. The GEFS has had a really bad warm bias this winter.
  25. Carvers Gap
    Also, my general rule for pattern durations is 4-6 weeks. I really just didn't' want to admit that at the time(Jan21st), but that has come to pass. If that rule holds, the can kicking into late Feb make sense. That means the actual pattern is Jan 21-end of Feb. I can almost use that rule and never look at an MJO cycle, and I should have done that this time around. It works almost as well as "thunder in the mountains." What we thought was a thaw, was really a true pattern change. I think on modeling we are actually watching models struggle w/ the next pattern change later this month. The beginnings of that change begin next week. Remember when the pattern was can-kicked by several days during December? Same deal IMHO. To be clear, pattern changes don't mean better snow chances. I am simply talking wx at this point. We need pretty incredible cold come March at this latitude. But I do think we are going to see a -NAO build. Is the EPS wrong? Possibility. But it really deepened that feature on the 12z EPS run. Normally, I would just say that warmth is coming and mail it in. But I am skittish after what happened during January, and modeling missed a monster cold shot.
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