Ground Scouring

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  1. Upstream convection in KS has definitely prevented the LLJ from strengthening as much as earlier models indicated by and after 00Z. 12Z GFS showed 40-45 kt at 850 mb by 00Z, with strong 10m response, when the actual winds are much weaker. Is that why cells have been HP in nature?
  2. Why are the storms predominantly HP today despite a lingering EML and strong UL winds at 300-200 mb?
  3. You can see the RFD already trying to undercut the organizing circulation near Mount Scott. Why is the cell HP despite strong UL wind profiles?
  4. Wichita County cell is clearly organizing as it heads toward Wichita Falls.
  5. Another major tornado may be coming N of Electra.
  6. New circulation could be trying to form SSE of Altus. Could it strengthen along the outflow boundary trailing the Snyder cell?
  7. Is outflow from the cell forming on the SW flank of the Snyder storm undercutting the mesocyclone? The tornado may have lifted. Rotation has weakened over time, which is fortunate, for the main rotation seems to be lifting north toward Snyder as the storm cycles.
  8. Marty Logan shows a possible rain-wrapped/multiple-vortex tornado on his stream. This is near Orienta, OK.
  9. The Fairview, OK, cell has some strong rotation as well and is TOR-warned. As an aside, the big cell in S OK is coming awfully close to Snyder (remember 1905?), but should miss to the south, unless it cycles in an untimely fashion.
  10. Quite the inflow you can hear on Jason Cooley's stream
  11. I wouldn't expect these cells to produce anything significant/long-lived (other than brief tornadoes) for another hour or so because the VBV in the lower to mid levels is just so stubborn. I do expect things to change later on, but right now I foresee some more mergers. Currently the Jackson Co. cell is stubbornly but tenuously holding on to its discrete mode in an otherwise somewhat messy mixed storm environment.
  12. Given favorable thermodynamics and strong low-level directional shear, why did the Shamrock cell and some of its neighbors undergo a merger? I'd expect them to return to discrete mode as better forcing arrives over the next few hours.
  13. I wouldn't necessarily say so. OUN shows very weak directional shear at 18Z (much less than at 12Z) due to a more unidirectional wind profile at 700-500 mb. That will need to change, and I currently expect it to do so, but currently the profile over C OK is unfavorable for long-lived discrete supercells. For a widespread outbreak, outflow boundaries alone won't cut it, but backed low-level winds will also help.
  14. Instability was too high on previous HRRR runs, but now it looks too low on the latest over much of OK. The 17Z run shows less instability over southern OK and the Llano Estacado at 18Z than has actually proved to be the case. Anywhere where cloud cover is thinning out is likely to match or exceed model output regarding instability.
  15. Given that SPC held the 15% for all of KS and only slightly trimmed the NE portion of the MDT, my sense is that the main factor precluding a High Risk is concerns/uncertainties over wind profiles toward late afternoon/evening, not instability. That leaves open the possibility that a High Risk could verify for parts of OK/N TX, especially since the trough appears to be verifying a bit broader (not as sharp) than past runs of the GFS suggested. HRRR and RAP are fairly consistent in indicating that the wind profiles will improve further toward and after dusk as the LLJ strengthens over OK/N TX. Special 18Z soundings could give the SPC the data it needs to go High later in the day (20Z).
  16. 1) Can you show me the less-than-ideal directional shear/meridional flow? 2) Can anyone show me the STJ that would cause less of an EML (or the factor resulting in widespread early convection)? I don't see it, and the ECMWF shows considerable destabilization on Saturday.
  17. There are still some synoptic issues to be worked out for Saturday--and will be until we get within 36-42 hours--such as the evolution of the piece of energy dropping down the west flank of the quasi-Omega (is that a good term?) block over the Yukon. The ECMWF has mostly favored a deeper solution to this piece of vorticity as it comes south off CA Friday/Saturday, and the GFS, while showing a much less conspicuous feature, has gradually trended toward the ECMWF (several runs ago it didn't even show it at all). If this feature deepens/consolidates, it could deflect the main trough over the Rockies even farther north as it ejects on Saturday. That would mean an even stronger EML, which could hurt the prospects for severe activity farther south (i.e., in OK), but would favor targets farther N toward NE/Dakotas. It could also impinge on the ejecting trough by forcing some height rises on its SW flank, narrowing wavelengths somewhat, but I doubt that this will affect the overall evolution of the trough itself (my interpretation could be wrong; if so, please explain why). What does strike me on the 18Z GFS is its reflection of a steady trend toward a more dominant EML overnight Friday/Saturday, based on the wind vectors. Given overall trends, I daresay that if early convection becomes a problem Saturday, it may be more due to bad timing of the lead impulse than due to a poor/non-existent EML. The 700-mb RH on the GFS shows late-morning convection over TX/OK, but it clearly seems more like forcing-related feedback given the decent quality of the EML shown. The 18Z GFS continues to show a more noticeable shift toward the ECMWF in terms of a more consolidated secondary vorticity maximum rotating around the base of the trough, which also looks more akin to the ECMWF in terms of breadth/wavelength and tilt. A few more days and better sampling of the Pacific are needed, but so far I am becoming a bit less worried/cautiously optimistic (pending more data) about the EML, which seems likely to be a more active participant on Saturday than it has recently--and look how recent events still ended up with significant tornadoes. I will also add that the GFS shows even more outstanding shear parameters on its latest run; if adjusted to account for convective feedback bias (meaning more instability), then the environment depicted would be more than sufficient for a major outbreak even with some back-veer-back present, which is not a given. Still, all this is preliminary, but the trends still look potentially ominous for a large part of the Plains. Check out the 18Z GFS soundings.
  18. I could be wrong, but is the 12Z ECMWF, while a bit deeper with the trough overall, a bit messier/less consolidated with the secondary vorticity maximum by late Saturday afternoon? Regardless, while the wind fields don't seem to differ much from those in the 00Z run, the arrival of the mid-level jet maximum/trough axis is a bit earlier than in the 00Z run. If I am interpreting the run correctly, that is why afternoon instability by peak heating is notably lower/reduced, apparently due to more convection developing around late morning/midday. Otherwise, the EML does not seem appreciably weaker (or stronger) than in the previous run. I am not placing much stock in one solution (one way or another), but I would like to know if my interpretation is correct. I would add that, overall, the 12Z GFS has shifted more toward the 00Z/12Z ECMWF than the ECMWF has shifted toward the GFS in terms of trough evolution.
  19. Regarding the subtropical jet and its effect on the EML in recent events, where should I look to find the STJ? Is it at 200 mb, 500 mb, 700 mb? Didn’t major Plains events like 4 May 2003 feature a STJ influence? Also, if the EML is at 700 mb and comes from the Sonoran region of northern Mexico, then why is a STJ coming from N Mexico a problem? Is the STJ within the same level as the EML or not? Can, say, a 500-mb STJ affect the quality of the EML at lower levels? If so, how? Maybe I am totally wrong, but I would like to gain some meteorological understanding.
  20. Since the ECMWF did not close it off too substantially at 96 hours, does that suggest that it has an edge over the GFS within that range, especially given the ECMWF's usual tendency to cut off lows too much/early? I would add that the GFS seems to be trending toward the ECMWF's evolution by Saturday, is it not?