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Carvers Gap

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  1. Carvers Gap
    The cold front is right on time. What is crazy is that this was a cold/snow time frame for weeks, and frozen precip was lost about ten days ago(roughly IDK). Now, it is back. Feb 13-14 has been the pattern switch for a while. Hopefully, some folks will get a quick thump. The 12z GFS on cue has now three fairly strong cold fronts throughout its run. It is anything but wall-to-wall warm. I'll have to look but 10+ days of that might be BN.
  2. Carvers Gap
    When the Canadian starts to produce real feel temps like this, it is probably at least worth passing attention. There is probably some bias in play here, but the Canadian can sometimes spot colder air masses before the GFS. If this is legit, it could snow deep into South Carolina and even the Panhandle. I don't think it does, but this solution would allow for it.
  3. Carvers Gap
    One thing which keeps my attention(rightly or wrongly), the warm-up from Jan 21 to now was originally forecast to be just a 3-4 day warm-up. It missed the MJO rotation into the warm phases, and the supposed hiccup of a warm spell lasted for weeks. There is part of me that wonders if that is happening right now, except the cold pattern continues longer than forecast. Modeling has been guilty all season of perpetuating a pattern and missing the turn. Now, I think there is good evidence that the warm MJO wins, but I don't think it is a slam dunk. MjO plots this morning tended to go COD in the colder phases, and that is something to watch in terms of trends. Now, I think warm-ups are inevitable...spring is going to fight this. But when I look at the 12z CMC driving single digits and low teens into the region, I do wonder if modeling is under estimating the embedded cold shots.....
  4. Carvers Gap
    ...and we are now left to fight inevitable spring with only the power of the one tone, wooly worm.
  5. Carvers Gap
    I know Cosgrove has mentioned that analogs point towards a warm spring w/ El Nino collapsing. This is also the time of year (shoulder season) where LR modeling will sometimes struggle mightily. All of that said, spring is not looking warm on LR ext or seasonal modeling. However, summer is looking very warm - meaning above normal. Given the performance of recent LR modeling and analog packages, I would say pretty everything is on the table for spring. I do think mid-late summer and most of fall will be hot/dry, maybe brutally hot if Nina kicks in.
  6. Carvers Gap
    Oddly, the 14th has been the day that we have looked at for a pattern change. To be clear, I don't think the new pattern is going to be all that great for snowfall in the valleys, but this would be a decent score for LR ext modeling. Of note, snowfall in forecasting is incredibly difficult to predict at range. Even when I do my "just for fun" seasonal modeling, I make a guess at snowfall...but it is like throwing darts while blindfolded. So beware, it can snow during a warm pattern. Here are the 12z outputs from meso scale modeling for the upcoming 14ths system. Nighttime is best option. I would not be surprised to see some folks in the forum area score if they catch this at night. This is probably a tougher sell for E TN unless you live near a break in the Plateau where moisture can slip through. Middle and west TN folks have a potentially minor or lollipop event to track. The ARW is not out yet, and it was bullish at 0z. I will add it here once it is completed. That map Tellico had this winter was really good about "flyways" for moisture entering the eastern valley. I was reading about a similar set-up around the Grand Tetons. I have always wondered why Jackson, WY, got so much less than Moran and Alpine. Those last two areas live near breaks in that mountain range.
  7. Carvers Gap
    Choose your own adventure book on CPC MJO plots this morning. The GEFS now takes a full rotation through the cold phases. The Euro does not. I like the 6z GEFS....it has a cold front on the 14th, 17th, and 25th. They don't have a lot of staying power, but that fits the wild MJO look. That MJO look should support a very transient pattern. I would lean base warm, simply because the warm days will likely be warmer against the norms than the cold days. As noted earlier, to score at this point we are looking for a well placed storm which would be timed to hit one of those cold shots. It would not surprise me to see snow showers next weekend. The storm for the 17-18th is not there. I am 50/50 on whether it returns. It is kind of in that window where storms are often lost. As for the 14th system, American modeling still has a pretty good thump for west TN as well portions of middle. The 3k NAM and 12k NAM both have rates driven snow which is crazy hard to predict. It would not surprise me to see some decent lollipops along the TN/KY border (middle and west). if American modeling is correct. As the 12z rolls in there are some pretty big differences between the 3k and 12k NAM. I am guessing modeling is struggling w/ rates driven stuff. It looks like the NAM favors a changeover in middle(and that is also nighttime which makes sense). The 12z changes over earlier in west TN. Whoever gets this system at night has the advantage. The Plateau may score some accumulation if the 3k is correct
  8. Carvers Gap
    18z Euro tried to get interesting as well for the Plateau. Holston went out and found a snowstorm to track.
  9. 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.
  10. 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.
  11. 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.
  12. Carvers Gap
  13. 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.
  14. Carvers Gap
    Wow. Check out the 18z HRRR....it has it as well. Right on time if real!!!
  15. Carvers Gap
    Yep, that is it. That is going to be a major loss. Thanks for the clarification. How long until that occurs?
  16. 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?
  17. Carvers Gap
    The 12z CMC definitely shows the potential for the trailing system around the 20th.
  18. 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.
  19. 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.
  20. 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
  21. 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.
  22. 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.
  23. 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.
  24. 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.
  25. 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.
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