2011-05-19 MISC: OK/KS/TX/CO

[Derek Weston]

Yesterday ended up being a bit of a letdown through the plains tornado wise. Kansas near the triple point, specifically. Why was this?

Pre initiation environment was quite nice from what I remember parameter wise. I expected a possibly appreciable outbreak across KS.

Ended up losing data in the field, however, and wasn't able to keep on the setup's evolution... so am left scratching my head a bit.

A few of my observations/guesses on issues with the setup:

- Shear vectors didn't pop things off the dryline well enough. Lots of storm competition. (though I've seen days like this where a highly competitive environment yields some nice results)

- Surface winds seemed lacking on the Kansas play per what I experienced on the storms we played. (we followed the first wave of storms north past 70) We saw storms try early on, lots of rising motion... but nothing could become sustained.

Still feel I'm missing something more fundamental here, though...

 

[Chip Redmond]

I feel that perhaps the shear wasn't quite good enough to allow storms to stay discrete and allowed them to have their updrafts cutoff by their own downdrafts. This created mostly HP storms and also prohibited any real long lasting supercells.

Chip

 

[Eric Bucsela]

I've been wondering exactly that and was thinking about starting a thread about the May 8-11 and May 18-20 systems. Both featured large western troughs (in May!) yet ~no torns in the Plains. Most bad seasons we worry about the longwave pattern (e.g. ridges, NW flow, etc), or simply about capping. But not this year. Is there a more fundamental problem?

BTW, since I think DISC threads have been discontinued, maybe the Mods will want to delete this thread or move it elsewhere.

 

[Jeff Duda]

I agree with Chip: it was a combination of not quite great shear (sufficient for supercells, but just barely), weak anvil relative flow (thus the HP storm mode), and the early initiation in SW OK. The left splits from those storms flew north and really destroyed the thermodynamics all the way north along the dryline in KS. Actually, the outflow from those storms began the retrogression of the dryline, which also hurt convergence and precluded further development until much later. Also, it seemed the only tornadic storms in KS fired on the triple point and had a hard time maintaining themselves when they wandered north of the front and lost instability. For whatever reason, the warm sector in KS remained capped enough to inhibit development despite what the SPC mesoanalyses were showing for SBCIN. Also, I think the warm front morphed and twisted and thus didn't make it as far north; the NW-SE orientation of the front slimmed the warm sector down even more.

 

[Jeff Duda]

I've been wondering exactly that and was thinking about starting a thread about the May 8-11 and May 18-20 systems. Both featured large western troughs (in May!) yet ~no torns in the Plains. Most bad seasons we worry about the longwave pattern (e.g. ridges, NW flow, etc), or simply about capping. But not this year. Is there a more fundamental problem?

I think the bigger issue with these two systems is the fact that both were closing off and obtaining a negative tilt as they did so, so the best flow was constrained to very near the upper level low (but the surface features were too far out ahead of the upper level features), thus shear suffered, and forcing also was reduced.

 

[Derek Weston]

Didn't know we discontinued DISC threads. (should have read more closely)

Responses:

From what I remember shear seemed to be decent pre-initiation. I thought we had at least a 50kt streak at 500mb (stronger just off to our west) and 30kt or so at 850. (assumed this would increase as the day progressed) Even the SPC issued a high end non-PDS tornado watch for KS. Jumped to a mod as well. (they at least seemed to side with me on a nice looking pre-initiation environment)

Fair enough point about the convection off to the south affecting the northern play...

 

[Brett Roberts]

One thing I found interesting with the storms in KS is how most were moving almost due N, noticeably to the left of the mean wind. You often see this early in a storm's evolution, but it seemed to persist for hours with most of the cells even as they matured, as far as I could tell.

Other negatives included extremely lackluster upper-tropospheric flow, another pronounced weakness in the flow around 2 km AGL, as well as a ~75 mb deep layer of horrendous lapse rates (nearly isothermal in some RUC soundings at 00z) around the same height. This also showed up on Wednesday evening's 00z OUN sounding, FWIW. Ultimately, I don't believe the observed and RUC-derived hodographs looked nearly as exciting as a lot of model forecasts from 1-3 days out suggested.

Even considering all this, I agree with others that it's fairly amazing to see such a large western CONUS trough in late May fail to produce a mentionable tornado event, even with good moisture in place. It always fascinates me how there seem to be "on" and "off" years where setups consistently either overperform or underperform in a given region, likely for reasons easily missed in the process of traditional ingredients-based forecasting. I'm sure a good chunk of that is simply a matter of perception, but like Eric, I have to wonder what we're failing to resolve (or recognize) at the current state of the science.

 

[Tim Vasquez]

(Just an administrative note in case anyone is wondering, this MISC category is re-authorized. See the Target Area rules in case you missed them. Thanks!)