Ground Scouring

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  1. Regarding the first point, I think my flaw was that I made an outbreak with several tornadoes seem insignificant on the whole, when I was only referring to the original outbreak area in N TX and parts of OK (and even there I was more wrong than right). There turned out to be more visible tornadoes and storm structures than I anticipated, not to mention numerous significant tornadoes (with a count still rising) that definitely caused substantial damage and loss of life. I also should have not overlooked the threat in CO/KS, where there were also significant, long-tracked supercells with strong tornadoes. I really don't know enough to be judging events in progress; even people with more experience and actual background would struggle with a difficult forecasting situation like that which existed on this past Saturday. I can come across as being unwilling to listen, and in fact I am too stubborn and prone to emotional/forecasting swings in many situations. I need to try better/harder to sit back, read, and watch, but sometimes I feel left out when serious questions don't get answered (sometimes understandably, based on my behavior). Regarding this coming Saturday: I must say that the 12Z ECMWF solution, taken ad verbatim, would almost certainly result in a major, quite possibly historic severe outbreak over a wide area, extending from OK/southern KS in the south to NE/SD in the north. What is critically important is that the ECMWF, as early as 96 hours, already begins advection of the first solid EML of the year, with a plume of high-quality inversion spreading northeastward from the Sonoran region over the southern Plains. More than a day and a half before the arrival of the deepening surface low on Saturday, there is already a robust EML in place over the southern Plains, and this EML remains in place through most of early Saturday due to the overall neutral tilt of the 700-mb trough. Moreover, there will be two full days of deep Gulf moisture spreading north, with a fairly strong low-level jet in place by 72 hours. As for the trough itself, the ECMWF has shown a notable shift toward a much broader, consolidated mid-level trough at 96 hours—an important trend as we get within the short range, the ECMWF’s kill zone. If the set-up at 96 hours verifies, then it will automatically have a significant impact by the time the trough ejects on Saturday. Shear is absolutely off the charts for mid May; even considering the ECMWF’s tendency to overdo the strength of the mid-level jet maximum, the pattern depicted would bring H5 winds of at least 55-60 kt into the warm sector Saturday, particularly over OK and southern KS, as a secondary surface low develops over the TX Panhandle. The orientation of the mid-level trough would imply fairly robust to strong backing of the surface winds all along and east of the dry line, extending well north into NE/SD. Such a set-up might also favor dry-line bulges (meaning low-level convergence as the surface low deepens) in OK and southern KS, where the best shear/instability combination seems to be present on the run. There is also no doubt that instability would be strong to very strong if the EML verifies as depicted. The very wide warm sector would also suggest a secondary severe threat along the retreating warm front in NE/SD (although the eventual location/evolution such a threat is more contingent on mesoscale details, such as early convection). All in all, the pattern on the ECMWF shows mid- to late-April dynamics juxtaposed with mid-May thermodynamics. In fact, it does so to an extent that I can’t recall in any previous Plains outbreak on or after 15 May. The overall pattern reminds me a lot of the late-May 1917 sequence, with a series of southern impulses gradually giving way to multiple large-scale, ejecting disturbances. If trends continue, I think that we may be looking at something very special this coming Saturday (and quite possibly Sunday over the Ozarks/upper MS Valley/upper Midwest, depending on how overnight convection and the upper-air pattern evolve).
  2. For the record, what do you think is likely to happen this coming Saturday? Honestly, I'd be more interested in your meteorological reasoning than another retort. You could also argue with anyone else who has been (justly) noting the lack of an EML, negative tilts/southerly tracks, etc. Argue with Brett or Jim (wxmann), for instance. A little fairness might be appropriate here.
  3. It might well come to nothing if we don't have a good EML. The trend toward a neutral/negative tilt with a "pinched" trough (i.e., one farther south with time) is not encouraging, as that would discourage a good EML from emanating over the warm sector. Anyway, we don't need more HP cells causing havoc for both communities and chasers.
  4. Why haven't they become more classical supercells yet? The net trend to me seems to be from classical to HP. I've tried to be patient, but this day just isn't really evolving much differently from what I expected (in terms of few or no visible tornadoes, other than in CO, and no long-lived events).
  5. The Eastland storm seems caught up in its own outflow...why are storms constantly developing on its SW flank?
  6. Are any chasers or stations streaming on the Cisco cell? I'm asking for links.
  7. This is north of Granbury on its current heading, which targets areas W and WSW of DFW--areas that are less densely populated than areas due SW of DFW. I consider the first major population center in its path (Weatherford) part of the DFW metro area. And on second thought, the distance between the cell and more back-veer-back profiles to the north isn't very great, which gives me more confidence that the tornado threat is conditional and might be even shorter-lived than I suspected. You can see how cells to the N of the southernmost one are struggling to maintain their isolation. UL winds might back even more over the next few hours as the UL trough approaches. Such would be good news for DFW and other, smaller population centers.
  8. I wonder if the gravity waves developing just E of that cell could offset the somewhat high LCLs. To me the tornado threat still looks conditional, maybe not worth the 15% (more worthy of the 10%), but maybe the cells need time to mature. One thing's certain: they're heading into the one area where very substantial instability remains (and will for a long period of time), with no back-veer-back anywhere. The good news is that the Pueblo (Callahan County, TX) cell really won't encounter high population densities for some time...until it gets to DFW.
  9. ...SRN PLNS TO ARKLATEX TODAY/TNGT... ANOTHER COMPLEX CONVECTIVE SCENARIO IS EXPECTED TO UNFOLD OVER THE SRN PLNS...WITH SEVERAL AREAS OF ENHANCED CONCERN. FIRST...HEATING ALONG DIFFUSE W-E OUTFLOW BOUNDARY OVER N CNTRL/NE TX EWD INTO THE ARKLATEX MAY BE THE FOCUS FOR SCTD SUPERCELLS/SUPERCELL CLUSTERS LATER TODAY INTO TNGT AS SFC HEATING DESTABILIZES AMPLY SHEARED REGION. COUPLED WITH WEAK ASCENT PROVIDED BY AN APPARENT UPR IMPULSE AND ASSOCIATED BAND OF ENHANCED SWLY FLOW ALOFT...SETUP COULD YIELD DMGG WIND/TORNADOES AND LARGE HAIL FROM STORM CLUSTERS WITH EMBEDDED HP-TYPE STORMS/BOWING STRUCTURES. The bold section--plus the location well away from the most favorable wind profiles--pretty much spells a non-event from a chasing standpoint. The 10% TOR doesn't cover the area along the dry line (including Childress). Given strengthening forcing, there is no way that the ongoing MCS over western OK will clear out shortly.
  10. From a forecasting standpoint, "salvageable" would mean nothing less than the resumption of yesterday's initial expectations--that is, a MDT Risk. Anything else would be a letdown, though technically not a bust from SPC's standpoint. Additionally, I can't remember the last time that a back-veer-back set-up with meager instability in early May produced anything of consequence--not after a continuous stream of MCSs wiped out a high-quality low-level air mass. Basically, all of the less-reliable, more-bullish models would need to verify, and even they show less favorable conditions in their latest runs than they did overnight (in terms of the UL set-up).
  11. The SPC won't bust on Day 1. Switching back to the original expectations--i.e., a MDT Risk or better--after such a drastic shift overnight would be unprecedented. I know that I've been criticized a lot here but the SPC's concerns about meager instability, back-veer-back, insufficient EML, etc. all match my original concerns from yesterday and preceding days (before and after I went along with the crowd and opted for a bullish outlook for today's "event").
  12. The 18Z NAM shows widespread 3-hr. precipitation of 0.35-0.5"+ over N TX as late as 18-21Z, following an MCS with totals over 1" (up to 4" or more!) passing over southern and eastern OK between 06-15Z. Compared to previous runs, the 18Z run also shows greater coverage of precipitation throughout Saturday until mid afternoon (peak heating). To me, with all that precipitation blocking air mass recovery (as the 700-mb flow will be from the SSW around midday CST Saturday), the destabilization shown by the NAM along the dry line looks overdone. Someone needs to enlighten me about the point in bold, since most of the back-veer-back on the models over the past few days has been at or above 350 mb, and others like CUmet were concerned about this back-veer-back, so I don't know why UL backing is less important than if it were at 500-700 mb, especially since, for tomorrow's event, the strongest wind vectors are at or above 350 mb, meaning greater divergence/ascent over the warm sector as on 05/24/2011 (though admittedly not to such an extreme level).
  13. The NAM shows back-veer-back extending well south and west of Enid, though not as far southwest as areas west of Gould and Vinson. The overall trend throughout the day has been to extended back-veer-back farther SW into OK. The 18Z run shows considerable stabilization of the warm sector through 18Z due to cold pools in the wake of early convection. Destabilization along the dry line thus only picks up considerably by and after peak heating (~21Z). A narrow sliver of 3000-j/kg MLCAPE along the TX Panhandle/OK border by 00Z tomorrow evening is really rather meager for the time of year, and the air mass, while of high quality and deep moisture, will be largely saturated prior to 21Z. The NAM shows storms firing along the dry line by 00Z, but then quickly dying off thereafter. I think that the main threat tomorrow will be large hail and a few isolated tornadoes, but nothing more. I see more of a hail threat than a tornado threat. I'd say 10% TOR and 45% hail probabilities.
  14. Well, tomorrow looks increasingly like a letdown--not because the UL trough is more negatively tilted, but because the GFS and the NAM have now trended toward a slower solution, leaving a notorious back-veer-back profile in the upper levels due to shortwave ridging. The unfavorable wind profile now extends well south into western OK on both runs, including along/just east of the dry line on Saturday evening. Given the lack of a stout EML early in the day, widespread convection breaks out all over the warm sector on the 18Z runs (including the NAM), and the day thus increasingly looks like a wash. Back-veer-back + insufficient instability for early May (due to early convection) is not a promising combination, even with somewhat stronger mid-level winds over OK. Given today's HP supercell profiles and everyone's earlier expectations for today and tomorrow, coupled with the lack of significant disturbances ejecting after Saturday (at least through the medium term), the overall trends aren't what I hoped they would be. And these are after I switched to a much more bullish outlook on tomorrow. Oh, well...
  15. The negative tilt of the 700-mb low as it takes shape early Saturday (at least on the GFS) helps prevent the EML from advancing northeastward over most of OK, thus partly allowing the early convection. However, the 06Z 4km NAM (and previous 4km runs generally) shows much less widespread convection than does the GFS and the main NAM. To be honest, I do not think that we're going to get a good handle on the convection until early morning to midday Saturday. Other than convection, everything else looks quite favorable for a significant outbreak. If convection ends up less than forecast, then a threshold-High Risk event becomes quite possible, if not even likely. Back-veer-back looks to be an issue at first but then quickly improves after 21Z.
  16. I hate to ask, but as I interpret the trends in the operational GFS for Saturday, is the model gradually moving not only toward a broader UL trough, but also a more low-amplitude UL trough? If so, could that cause the badly timed lead impulse (which helps spark a lot of convection over part of the warm sector in OK by 18Z Saturday), currently depicted strongly on the 18Z run, to be weaker/faster-moving than currently indicated?
  17. Actually, I like the fact that the heaviest convection over E OK before 12Z is much less widespread/moves out more quickly on the 12Z as opposed to previous runs. Plus, the overall evolution of the trough has been to favor a more rapid ejection and a broader, more consolidated mid-level feature, thereby greatly alleviating the veer-back-veer not just before 00Z, but also well into the overnight and early morning hours. The ECMWF and the GFS now seem to be inching toward better agreement on the timing of large-scale ascent and ejection, and the overall net trend is faster and more favorable for a significant severe outbreak on Saturday--one with a potentially long-lived threat for supercells/significant tornadoes overnight. So my concerns at this point are starting to diminish. As far as low-level shear is concerned, doesn't the GFS have a low bias in these cases? To me, what matters is the overall synoptic set-up, the improving thermodynamic prospects (at least before 18Z), and the strengthening low-level jet into the evening hours/overnight. Initiation time will still need to be nailed down, but fortunately there is ample time for change. The GFS is probably suffering from convective feedback due to WAA.
  18. While I'll concede that the drought has been alleviated somewhat, the long-term conditions (per U.S. Drought Monitor) still indicate a fairly substantial area of ≥D2 conditions over the TX Panhandle/N TX, western OK, and extreme southwestern KS. Although recent trends are in the right direction, we will need to see much more substantial rainfall over a longer period of time--and over a wider section of the worst-impacted areas. Tonight's heaviest rainfall (especially in the OKC metro) is mostly falling outside the worst drought areas mentioned previously. The Red River area of N TX / SW OK needs a lot more rain than it is currently receiving. So I will still stand by my statements, with a modification that the drought conditions, as I mentioned, are but one factor. While Saturday, 9 May, may see a widespread severe event, whether it is chase-worthy will still depend on the other caveats (non-drought-related) that I and others mentioned. As of now, I do not like the relatively weak deep-layer shear on the models, which is not much greater than that which occurred today over the warms sector. Thus, we may well see many HP events with the supercells that go tornadic. We will need to see major changes in both the ECMWF and GFS solutions toward stronger wind profiles to offset this threat. The back-veer-profile will obviously be a concern as well, even though trends indicate that early convection may (and that is a big if) not be a significant impediment to the overall set-up. And overall trends favoring a delay in the arrival of stronger forcing are a third negative factor. So we will need to see changes in both the timing (unlikely as the ECMWF is superior within 84 hr) and the form (also somewhat unlikely) of the trough on 9 May.
  19. Pardon my question, but with such favorable thermodynamics in place, why are the storms near OKC outflow-dominant?
  20. I'd say that the threat for tornadoes from the Chickasha cell will diminish as it enters the higher LFC to its northeast and as 500-mb winds increasingly veer, promoting a back-veer-back pattern that will engender more cell mergers. The strongest upward forcing has already passed anyway.
  21. For Saturday (9 May), I see a lot of problems with this set-up, +PDO/drought climatology and past performance not least, but also including the potential for back-veer-back at 850-500 mb, the relatively weak wind fields (making mesoscale factors like moisture return all the more critical), and the likelihood for drier low-level air to scour out low-level moisture in the eastern Gulf (thanks to our developing subtropical sloppy off the SE coast). The high model variability in the short term would favor the ECMWF solution, which is slower and delays the arrival of more significant large-scale forcing until early evening. If other factors conspire against this set-up, then the slower arrival of forcing would be a deal-killer. While early signs in other respects may appear promising, I would bet on a combination of a few factors limiting the tornado threat to perhaps a few brief touchdowns. I could be wrong, but I would not bet against the seasonal trend.
  22. No, or at least not necessarily. Land and even marine data coverage after 1900 is actually pretty decent in the U.S., especially from the 1920s onward. We have pretty good evidence with which to determine the size and intensity of landfalls in the same period. For instance, we have good data to show that 1900 Galveston, 1926 Miami, 1928 Okeechobee, 1935 Labor Day, and the 1932 TX hurricanes were at least 120 kt at landfall (with the latter three 125-130 kt, if not a bit higher). Based on data from the last active cycle (1926-1969) compared to those for 1995-present, the recent cycle, even when compared to a similar 15-year period in 1926-1969, has seen a noted decrease in the frequency of upper-end majors (Cat. 4/5) making landfall. Also, there has been a significant net decrease in the frequency of major landfalls; note that practically all the major U.S. strikes since 1995 occurred in just two seasons, 2004 and 2005. While major hits have tended to frequently cluster in other cycles, the major hits in 1926-1969 were more frequent and the clusters more closely spaced. The late 19th century lacks significant data, but when this is taken into account, some evidence indicates that 1851-1894 may have featured at least as high a frequency of major landfalls as did 1926-1969. Basically, the latest active cycle has for the most part underperformed relative to the past. We haven't seen a reasonably large-sized, high-end major event (Charley was tiny, while the other Gulf majors were all Cat. 3, not Cat. 4/5). Also, SSTA data seem to indicate that the latest active cycle may already be ending prematurely, though that remains to be seen.
  23. I really doubt that climatology is as useful as people make it to be in the new normal as the overall global circulation has changed due to large-scale issues that aren't really being addressed. What about the shift in the South American heat low? Why has that happened? Has seasonal variability decreased in some time scales due to more persistent mid- to upper-level patterns (i.e., a wavier flow)? Why has the THC decreased? Should such an index really take into account a bunch of variables that are unrelated to each other, thereby masking some unknown influence's effect(s) on factors that directly affect each other? The only really compelling reason, in part, for the slowdown in MDR development is a long-term drought in West Africa, but even that doesn't explain everything.
  24. Since 2010, we have only seen one official Niño, that of this year (2014-5), and yet we have seen the same pattern--lower-than-normal (for an +AMO cycle) instability basin-wide, higher-than-average vertical shear in the Central Atlantic, W Caribbean, and Gulf--in practically every season, with the possible exception of 2011, which still featured less favorable values than in other years prior. In fact, most or all of the usual indicators favored an active season (with a strong, west-based Bermuda high in at least a few of the peak periods) in several of these seasons (2012 and 2013), yet expectations simply did not pan out. No one has really come up with a convincing explanation as to why. Drs. Gray and Klotzbach, despite their (deserved) reputations in some areas of seasonal forecasting, did not offer a tested hypothesis to account for the reduced activity; their NAO/AO explanation (that the NAO/AO somehow contributed to reduced instability) is, to me, insufficient without taking into account other factors. Otherwise, it is simply not supported by history or their past studies' criteria. In my opinion, instability and shear are both equally important, but may affect different aspects and areas depending on their location. Experience, to me, has shown that these factors can easily nullify higher-than-normal heat content. Unfavorable conditions in the Central Atlantic shut down the MDR; similar conditions in the W Caribbean/Gulf shut down homegrown threats. Result: higher-latitude fish activity. Having looked at available evidence, I think we may well see record-low activity this season with only a tenuous land threat to Bermuda and E Canada (another Fay or Gonzalo, perhaps).