2013-04-17 MISC: OK

[Brett Roberts]

A few miscellaneous observations and comments, without trying to take a hard stance as to the exact failure mode on Wednesday:

*I don't really recall 2007-03-28 displaying prominently S-shaped hodographs on forecast or observed soundings. If anything, there may have been some concern over backing in the upper troposphere, but not around 700 mb as was observed this week. For example, the 2007-03-29 00z DDC sounding shows nice veering up to 500 mb. Moreover, barbs on the 500 mb chart appear uniformly more veered and stronger than on the 700 mb chart; this, too, differs significantly from the analyses on Wednesday evening.

*Personally, like Jeff, I can't recall any great tornado days -- or even good structure days -- that I've chased where a major weakness around 700-800 mb yields the nasty S-shape we saw on Wednesday. However, that's just anecdotal, and it's only something I tend to notice if it's fairly severe -- which it was on Wednesday, in my opinion, especially on the RAP the day of the event.

*Despite the jumbled VPPGF distribution that can be inferred for updrafts in Wednesday's environment (due to the S-shape), it seemed like all the supercells turned well to the right of the mean wind. On Wednesday morning, I was very concerned that 500 mb flow was verifying more meridional than expected, which could carry storms quickly across the boundary unless they were right-movers. Despite mid-level flow that was nearly SSW, though, the storms trained in a WSW-ENE fashion from FDR to LAW all day.

*Regarding the issue of warm mid-level temperatures: isn't CINH integrated only from the surface to the LFC on most model output? In that case, it is theoretically possible for reduced (or negative) buoyancy to play a major role in an environment characterized by minimal or zero CINH. The 00z FWD sounding exemplifies this well. However, I don't believe it was very representative of the supercell environment 100 mi. to the NW. I noticed some model soundings with a weaker version of the same warm nose for areas like LAW-OKC, but as you dropped farther SW (especially into NW TX), it eroded almost completely by late afternoon. Even so, the southern dryline storms that initiated late struggled a lot.

 

[Jeff Duda]

I'm pretty sure there has been research in the recent past on lightning activity in tornadic storms. I'm pretty sure there is a characteristic signature called a "lightning jump" wherein lightning activity significantly increases, then significantly decreases in a supercell storm minutes before tornadogenesis.

With the above said, I can recall chases with very little lightning activity that were prolifically tornadic as well as very electrical storms that were not at all tornadic.

 

[Joshua Nall]

In response to Stexan...You can absolutely have a nasty supercell with tornado on the ground and there be no cgs. I'm talking about for 15 minutes, never see a good bolt. But then you can get a little high based LP that will just go crazy shooting out the most beautifully branched bolts, as many as 4 at one time.

I have also noticed that cgs come in spurts. Haven't payed enough attention to say absolutely when with regard to the area surrounding a mesocyclone, but for instance on a pop up summer type storm the most numerous bolts will be as soon as the first heavy rain shaft starts to descend. If you see a bolt a new place where there had not been any, then you had better get your camera pointed over their quick for a few more. Then when the rain shaft gets to going that will be it.

 

[Dan Robinson]

Just from pure observation, most of the supercells I've seen (tornadic or not) had more positive CG activity (the branchless downward bolts) in the forward flank precip than negative CGs in the updraft region. Mulvane was the only storm I can remember with frequent negative CGs around the updraft, and even then they didn't seem to follow any pattern before, during and after the tornado.

Since lightning is likely more tied to the larger-scale updraft and in the higher regions of the storm, I don't think there can be much of a correlation between lightning and tornadoes. Tornadogenesis occurs in the very lowest levels of the atmosphere tied to processes in the boundary layer, a region that doesn't play a part in charge generation. You could have two identical supercells with lots of lightning - if one is rooting on a boundary, it's going to produce, the other won't.