6/18/07 FCST: TX / OK / KS / MO / IA / WI

[Jeff Snyder]

This post will address the S-of-I70 area, but the thread is valid for much of the central US...

The combination of strong instability and "interesting" wind profiles across the KS / OK / TX area tomorrow intrigues me. 00z/18 NAM forecast soundings valid tomorrow evening shows a fascinating (to me, at least) range of hodographs... In an "upslope" region across the northern TX panhandle, SW KS, and se CO, many of the hodographs are straight-line, but with most of the line displaced in the bottom half of the hodograph (not the typical top half), with 40-60 kt 0-6km shear (ok, "vector difference"). For example, see http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_overlays.cgi?fcsthr=024&STATIONID=KDDC

A little farther south and east, forecast hodographs show more of a curved shear profile, with some respectable (by mid-June standards) "loopiness" across southwestern Oklahoma and western N TX. Though flow aloft is relatively weak, there is enough directional shear to still yield ~35kts 0-6km shear. For example, the hodograph at LAW is pretty nice: http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_overlays.cgi?fcsthr=024&STATIONID=KLAW

Between the two areas, the NAM is showing some cyclonic curvature to the hodograph, which looks to favor left-splits / mesoanticyclones --> http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_overlays.cgi?fcsthr=024&STATIONID=KGAG

All locations show strong instability (CAPE 2000-4000 j/kg) to support robust updrafts and little capping by 00z. It seems that the depth of moisture becomes more of an issue as one goes farther northwest from western Oklahoma, but no areas in the TX / OK / KS area seem to have much in the way of sources for UVV aloft. With the primary shortwave trough lifting well to the north, any related DPVA will also slide well north of the area. In addition, the GFS seems to keep the strong flow aloft farther north, with really marginal mid-level flow south of the OK / KS border (15-20 kts, compared to 30-35kts on the NAM). Finally, there may not be much in the way of substantial low-level convergence as winds veer behind the front.

The moderate to strong CAPE and sufficient deep-layer shear should yield a supercell threat across the southern and central Plains tomorrow. I'm not too hot on the lack of mid-level forcing (something which is shared with the 6/7/07 bustola in OK), and the questionable surface convergence may make it difficult to pin-down a target. But, given the time of year, I can't pass up a possible OK chase tomorrow. Personally, I think my decision on whether or not to chase will come down to the strength of the flow aloft tomorrow, which may well be the difference between multicell garbage and supercell love... If the GFS looks like it'll verify, I'll probably sit out; if the NAM looks like it'll verify, I'll probably make an effort to head out.

 

[Jeff Snyder]

Wow, no other posts, eh? I think there's a decent potential for a tornadic supercell in western OK today, as extremely unstable condititions develop through the afternoon (15z RUC was showing >7000 j/kg, with peaks over >8000 j/kg in western north Texas). Currents obs hint at a possible OFB across western and southern Oklahoma from ongoing and earlier convection that caused major flash flooding in parts of southcentral OK and northcentral TX. At any rate, clouds have impeded low-level warming a bit this afternoon, but a transition to Cu has allowed temps to rise to the 86-91F range in southwestern OK. With Tds in the low 70s (and even some 73-74F tds E and SE of Lawto), LCLs are manageable (<1400 m). In addition, winds have backed a bit in western and southwestern OK, which has helped to pump deep-layer shear into the >30kts range (even despite the 20-25kts 500mb WNW or NW flow). Latest models hint at strongest low-level shear shifting a tad south into and south of the Red River area by evening. Regardless, the presence of a boundary may make things very interesting.

Primarly concern for me is the capping vs. convergence balance. Current mesoanalysis indicates quite warm 700mb temps in the TX panhandle and adjacent portions of far sw KS and western OK. Temps in the low-90s and Tds in the low-70s should have remove the cap, as mesoanalysis currrently indicates. In addition, thre may be some subsidence aloft occurring on the back side of the departing midlevel low that has meandered around this area the past several days. In addition (x2), I'm not sure there's a whole lot in the way of surface convergence. The OFB may provide some, and the cold front that's across extreme NW OK may provide more. However, winds behidn the front should veer with time, leading to frontolysis and decreasing convergence. Will storms develop this afternoon? Current sat indicates a large Cu field across western OK...

I may head out with my chasing amigos to the Clinton - Hobart area soon. I can't ignore the setup -- strong to extreme instability, sufficient deep-layer shear (>30 kts), good directional shear, moderately-low LCLs, and a boundary all lead me to think that there's the potential for a tornadic supercell somewhere in western OK today. Sure, not a big event by any means. But it's mid-June, in the southern plains, so I'll be just fine with a good supercell.

EDIT: Despite my reserved optimism for SOMETHING in western OK, it seems that the last SWODY1 whole-heartedly disagrees with this. Ouch. Oh well -- there's a 2%-5% tor prob in the area in my forecast, for what little that's worth.

 

[MatthewCarman]

Jeff I only see a 2% chance of a tornado by the SPC. Do you see anything that points to a possible tornado outbreak or just isolated tornadoes?

Here in Iowa nothing more than Nickle sized hail and mabey some isolated winds to 60 MPH. Looking to be just your normal everyday thunderstorm. I noticed a 30% chance of severe winds across WI but I just feel things will be mostly linear up there. I would want to play the southern area for more isolated stuff if I was chasing today.