SLT was to the NE of the meso early on with eyes back toward the SW. This is good positioning .... Then they drive east as the storm gets closer
Totally agree.
and a new area of broad rotation and convergence takes shape to the N of the previous velocity couplet, which seems to be weakening.
This is where both their chase starts to go bad, and where our understanding of this storm diverges. One of the points I'm going to try to convey is that, what appears to be the center of broad rotation on velocity, is not actually where the storm's low level mesocyclone is located. The area to the north is the inflow and RFD surge that kicked off tornadogenesis, and these surges are not located where tornadogenesis would eventually occur.
Davies' analysis shows the next cycle of the mesocyclone, the broad rotation indicated on velocity to the north, initially tracking southeast, before it then turns left to the northeast, just as it produced the EF4, following a very similar course as the previous EF2. Doesn't that southeast motion strike you as bizarre, and the turn to the northeast to follow the same track a strange coincidence? I'm suggesting the "storm" and mesocyclone were not moving southeast and then turned northeast. The rotation, and indeed convergence to the north, were winds feeding into a mesocyclone that was *always* to the south. The area to the north was converging inflow band. I hope to have some really strong visuals and analogs for the presentation so that you don't have to just take my word for it here, but that's the point I'm going to try to argue in case you guys have better ideas or additional feedback. But I think one can make a really strong case for this by not getting hung up on (and perhaps misinterpreting) the velocity. The reflectivity shows the same structure, moving northeast the entire time. The visuals of the storm itself, what should be the most important decision making "data", show the same structure, moving northeast the entire time. Yes, the EF4 may have actually turned left as it was developing. It was probably orbiting the rim of the mesocyclone before it settled in the center. The parent mesocyclone, however, was always moving northeast and was always on that same northeast track which produced both tornadoes.
how was SLT to know they were not hit by a satellite at the time?
The visual structure indicates the impacting EF2 was colocated with the primary/mature mesocyclone cycle. The visual structure indicates this is where you'd expect the main tornado to be, not a satellite. It's a misinterpretation of the radar to think of it as a satellite at that point. That evolution came afterwards because, again, the area to the north was not the location of the next cycle, it was mainly the winds converging into the next cycle. This will make more sense with some visuals I hope.
Seems no one knew the ef2 existed until they were either impacted or nearly impacted.
Both the NWS and broadcast media had a really solid handle on the couplet that produced the EF2. I don't fault chasers for not following every second of the radio and matching it down to the street. But the tornado warning absolutely pegged this tornado. The media had the location down to a T. Both with ample lead time. I'd hope chasers are following one of those sources at least. This tornado was not a surprise.
Generally new tornadoes come from new areas of the updraft. If the EF2 was basically spinning itself out, then I don't see that meso causing the EF4. A new area is what SLT would have been trying to get into position to see. And an area to watch for new development, based on velocity data, was to the North.
You're totally right that the EF4 came from a new cycle. You often see that new cycle displaced to the north. But it wasn't on this storm. That cycle occurred in the immediate vicinity of the old one. That's probably why the EF2 acted like a satellite. There simply wasn't enough spacing as the storm cycled and it got entrained. I have a really good analog for this too (Pilger/Wakefield). For whatever reason, maybe shear vectors keeping the cycles on the same line, the new meso developed on the same track as the old one.
Another thing I have trouble with is that radar shows Quincy to be inside the bounds of rain produced by the storm rfd, but his video at the identical time seems to contradict that and shows what appears to be HP structure to the W.
I was really surprised to see how well the RFD core and RFD gust front were defined on this storm. Looking at the reflectivity initially, I'd have imagined SLT drove into steadily increasing rain with 0 structure and a tornado somewhere in the middle of that. But instead the visuals show really well defined Bear's Cage structure. I think this is simply a limitation of the reflectivity at that range. The beam is hitting a few thousand feet up into the storm, where there is no doubt a ton of precipitation loading. If the 88D was closer, you'd probably see a much tighter ball at the end of a hook. There was pretty decent precip falling ahead of the RFD gust front too, however, so it wouldn't have looked totally clean.
The new area, whatever you want to call it appears to be around a mile to a mile and one half N at the time of the incident. SLT claimed 2 miles. That is a reasonable misjudgement.
One might be mislead into thinking so looking at the velocity. The visuals, however, showed the new area forming basically on their heads.
So is all of this occurring behind the rfd gust front and heavier rain
Yes.
The chaser hopes that a cycle occurs in (relatively) clear air to the north/northeast when positioning in the notch of an HP, or at least on the RFD/inflow notch interface where it's still somewhat visible. And indeed this is probably what everyone was doing when they were gunning for that position (if they knew what they were doing). However, this storm did not cycle in such a fashion, to the northeast in the notch. It cycled just behind the RFD gust front, maybe a half mile from the old cycle and ongoing tornado. I really hope that visual examples in this presentation make a strong case for this. It's a grave mistake to get in the notch, see no tornado, and then turn a blind eye on the dangers lurking in the mature Bear's Cage of which you're about to core punch.
If nothing else, questions can help with knowing what even needs to be addressed.
Yes, thank you. These discussion have helped tremendously in highlighting the areas that most need our attention. Hopefully a video presentation with such focus can do some real good in advancing chaser safety, rather than simply describing how a colossal screw-up happened.
