2015-04-08 EVENT: KS/OK/TX/MO/AR

[Matthew Crowther]

The cell SW to NW of ICT did produce a few tornadoes, a couple of cones and ropes according to storm reports and a couple of FB pics I have seen. But in general, pretty underwhelming....

 

[JamesCaruso]

I find it most constructive to do post-mortems; it is always harder to find post-event analysis, especially for the events that disappoint, compared to the amount of pre-event analysis and forecasting! So here are just some observations, I look forward to thoughts from those better at interpretation... Apologies in advance if the images do not display near the associated paragraphs!

SPC issued a meso discussion for the area of interest at around 19:20Z. The triple point was shown to be already near or east of ICT.

The 20Z surface map showed Gage, OK at 90/33 with a NW wind. At this time, only SW OK has favorable T, Td and winds. Elsewhere, winds are veered in the warm sector. There is crapvection near Chanute in SE KS, outside of the TOR watch.

By 21Z, the dryline is showing signs of retreating westward. Gage is 85/59, winds SE at 25. Still, aside from along the dryline into SW OK, there are not many surface obs that look good east of the triple point, except near the crapvection in SE KS.

By 22Z, the dryline has further retreated and the triple point itself has also shifted (reformed?) westward, probably west of Medicine Lodge?? Gage is 81/61, winds SE at 30 with gusts to 37, and the pressure has dropped to 999.2. Alva is 81/63, winds SE at 20 with a thunderstorm.

Here is a radar image from about the same time.

I think it was Jeff Duda that mentioned, in the Reports thread, the negative effect of thick high clouds. Were there also issues with the dynamics and/or their timing? It seems like the surface pattern was a little more diffuse than I expected it would be near and east of the triple point, but sharpened up later as the dryline retreated and the triple point itself shifted/reformed - perhaps in response to the approach of the upper support and cyclogenesis in Colorado??




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[Jeff Duda]

I think it was Jeff Duda that mentioned, in the Reports thread, the negative effect of thick high clouds. Were there also issues with the dynamics and/or their timing? It seems like the surface pattern was a little more diffuse than I expected it would be near and east of the triple point, but sharpened up later as the dryline retreated and the triple point itself shifted/reformed - perhaps in response to the approach of the upper support and cyclogenesis in Colorado??

Other than digging up some SPC mesoanalyses from last night, I don't have a lot of concrete evidence, but it seemed to me that the main vort max/disturbance never really ejected over the plains. The 00Z 500 mb chart (below) shows the trough was still pretty broad with an axis along or just west of the CO/UT-NM/AZ border region at that time...seems a little too far west to really provide strong lift over OK/KS, but perhaps I'm wrong about that. There are other "wobbles" in the height pattern suggestive of subtle impulses, but I don't see anything that looks like it would've favored initiation in NW OK/TX PH.

Furthermore, the thermal axis at 700 mb at 00Z was still well west of the longitude at which this event occurred (roughly over the KS/CO border and southward, see below). To me this corroborates the notion that the best forcing was still to the west of the area of interest. Furthermore it meant there was a greater tendency for more CIN to build in. The capping inversion was based more around 850-800 mb, and I don't think there was much cooling that level, so those two facts put together explain the CIN building back in so early.

Reiterating from my post in the REPORTS thread - combine the not ideal forcing with the thick cloud deck that shielded the sun everywhere and I think that explains 99% of why this event underperformed.

The other 1% goes to SPC IMO: 15% hatched at the 1630 UTC update #15hatchedtorSPCkissofdeath? What did they see? I was telling my chase partner Logan before we left that they should've downgraded at 1630 to 5% tornado.

 

[samuel stone]

The beauty of chasing is you can still have a great day even if the event as a whole under-performed. (i.e. anyone who caught 1 or 2 of the tornadoes on the medicine lodge storm, or a few cases of great structure in western Oklahoma. I saw my first tornado since May 28, 2013 and I nailed the target and intercept of the medicine lodge cell so i came away feeling very satisfied, I think it made it more satisfying knowing that it wasn't necessarily easy to pick the right target on this day and even harder to stay with it when the initial storms just weren't getting their act together, throw in the difficulty with getting into the right position in the vast hilly roadlessness of the red hills in Barber county and it really felt great.

But i do agree with all the factors leading to a largely sub par day for most, honestly everything that went wrong was exactly what the models had been trending toward the last 48 hours but just maybe even a little worse, veering surface winds, veered hot dry 850 winds, widespread warm sector convective messes, weak forcing/narrow spatial and temporal window for favorable CIN.

Although I was pleasantly surprised by how quickly the surface winds did back between 20-22z near the triple point, i was really worried about that at 18z

 

[Jeff Snyder]

@Dan Dawson and I sat at the intersection of SR14 and US 64 west of Alva / N of Waynoka for about 20-25 minutes debating about what to do. The supercell coming into west-central Oklahoma looked pretty good on radar, but the upstream near-surface thermodynamic environment looked poor. I've uploaded a map of Oklahoma Mesonet data valid at 2230 UTC (5:30 CDT). The color fill represents 2 m temperature. There was a single row of counties in far western Oklahoma that had temperatures of 77-82 F; similar temperatures were located along the northernmost tier of counties in northwestern Oklahoma. Otherwise, temperatures had dropped to 72-75 F across most of western Oklahoma owing presumably to the cloud cover and perhaps some residual effects from the earlier elevated convection. Both the 00z OUN and 00z LMN soundings had a convective temperature of 90 F, or a full 15-18 degrees F above the mesonet obs from Seiling southward. That was much too high of a hill to climb. At any rate, we knew this when we finally decided at ~5:45 pm to drop back southward, with the hope that strong enough VPPGFs could be established to allow the storm to remain surface-based as the LLJ increased. In addition, the storms near the OK/KS border were continuing to look strung out as they initiated off a "hot point"/source near Buffalo that was continuing to lift northward into KS. We were very concerned about chaser convergence in KS. We were also concerned about PBL cooling associated with the elevated storms (we could see the updraft bases -- they were very, very high) between the western OK supercell and the OK/KS convection. At least one or two supercells did develop back upstream across the OK/TX border, one of which earned a tornado warning after dark. Temperatures were similarly-cool at this time (when the storm was NW/N of Clinton), but I suspect the shear and mesocyclone were strong enough to allow surface parcels to be lifted via dynamic processes despite robust negative buoyancy through the capping layer.

I think we had SW 850 mb winds until at least 18z yesterday across much of the warm sector, and WSW 850 mb winds before then. The flow at that level did back to SSW 00z (at least as sampled by OUN and LMN), but the damage had already been done. Of course, if the base of the EML had been cooler to allow for weaker CINH, we would have seen worse lapse rates and lower <3-4 km buoyancy. The key, in my opinion, was the cooler-than-anticipated surface temperatures. Put in a wider corridor of 82-85 F temps, and I think we would have seen the event develop differently. Some question remains as to when it became apparent that the low-level thermal field was not going to warm sufficiently over non-narrow corridor, though. To us, that was certainly apparent by 5 pm, when OK Mesonet data essentially showing that OK was going to get shut down.