02/28/07 DISC: KS/MO

[Verne Carlson]

Hi Evan,
Who was the off-duty NWS employee who shot the footage? I would like to contact them for possible inclusion in the Storms of 2007 DVD. Anyone else who got video from this night please PM me.
thanks,
Verne

 

[Evan Bookbinder]

Verne,

That person is on this forum -- it's up to him if he wants to get ahold of you. The video dub we got was VHS and extremely grainy -- although more than sufficient for our purposes. If his original is digital, then even I would love to see it!

John,

The path length based on connecting all my GPS survey points was about 24 miles. Greatest width (subjective between damage and video) is between 1/4 and 1/2 mile wide. There was just so "little" to hit, but we should have areal photos shortly which should help determine how much of that wedge was actual tornado.

Evan

 

[Rich Thompson]

We got video from an off-duty AWC forecaster who was coming up the from the S out of Blue Mound -- it's a biggy. What's amazing is that there's no evidence of the tornado "increasing" in size from touchdown, as one would typically expect. This may be due to the extreme low LCL heightsand incredible shear -- (DPDs were on the order of 1-2F from a nearby weather station with low level SRHs estimated at > 1000!!). It basically goes from a wide funnel with multiple tendrils to a large wedge in very short order.

Evan

Evan,

What did you use to estimate the > 1000 m2/s2 SRH? I've reviewed the SPC mesoanalysis graphics, and I don't see anything larger than 300-500 m2/s2 (which is pretty large) for either 0-1 km or the effective inflow layer. We were using an estimated storm motion from 240-250 degrees at 25-30 kt in our SRH calculations.

Rich T.

 

[afischer]

For anyone wanting to create a modified sr-hodograph for this event, the wind profiler data may be helpful. For instance, ambient 500m agl winds of 40-50kts were sampled, per Neodesha KS profiler.

http://locust.mmm.ucar.edu/case-selection/dates/20070228.html
http://locust.mmm.ucar.edu/case-selection/dates/20070301.html

 

[Mike Peregrine]

Doesn't look like anyone has posted the link yet, but the additional page with rating information, vid caps and radar imagery can be found here.

 

[Mike Peregrine]

Also, it is pretty miraculous that this large tornado essentially remained in rural, open country. I think we can all be thankful for that.

Amen to that. If this had happened even 20 miles north of where it was, it could have been disasterous. Even if it had been just a couple miles off the track in either direction, it would have been in line for some small towns. Having that intense of a tornado this far north so early in the year is what amazes me the most.

What a crazy storm ... >1000 m2/s2 is insane. Was the storm influencing the local environment somehow? That's a crazy big SRH number.

 

[Eric D B'Hymer]

Winds back to a more southerly direction and the dewpoint rises from 25F at 3 pm to 52F at 5 pm. Next time I will examine the advection of the air masses more closely before heading out!



Alex, i was truly amazed that this dewpoint shift happened myself, i live in Iola 20 miles north of KCNU and i had read the MD that the SPC had out about 2 0r 3 pm and i was like no way, it staed the dryline would retreat to the west as it was stalled on the KS-MO border in the afternoon. Then about 5 the wind switched from sw to the s -se and it got humid real fast and thats when the elk county storm started.

 

[Evan Bookbinder]

Evan,

What did you use to estimate the > 1000 m2/s2 SRH? I've reviewed the SPC mesoanalysis graphics, and I don't see anything larger than 300-500 m2/s2 (which is pretty large) for either 0-1 km or the effective inflow layer. We were using an estimated storm motion from 240-250 degrees at 25-30 kt in our SRH calculations.

Rich T.

Rich, I find it a tough number to swallow, and these were given by my SOO who had gone back through the data. I'm not sure how they were calculated, but I do plan on doing an extensive analysis and making sure that correct calculations were being made. I didn't mean to haphazardly throw numbers out there, although 1000 is not unprecedented (measured at the Haviland, KS profiler May 7 2002 when a large wedge passed very close to the site).

I will be in contact with you and Glen once I get some time to analyze the data. I think, as Glen pointed out, the DPDs were more realistically like 4-5F in the inflow region. Calculated Storm motion was IRL, 240 @ 30-35 knots. I guess the key to insane low level SRH calculations would be the sfc wind vector. I noticed that SGF's 04Z sounding has a > 500 SRH with a surface wind of 150/10 knots. Some of the mesonet data in the vicinity of this surpercell suggests that the wind vectors immediately south of the FFD boundary were from the E/NE. Now, of course we'll never know the true inflow wind as I'm not aware of any chasers who were in this location, but we've all chased enough storms to know that these winds can be 20-40 knots greater than the ambient flow ahead of strong supercells, which could lead to some insane low level SRHs.

Evan

 

[Glen Romine]

I'd just add that, and I presume that Rich was thinking along the same lines, that the moisture depth for this event probably was much less than 3 km. Effective helicity therefore is going to use a much shallower layer (more like 0-1 or 0-1.5 km at best if there was some local moisture pooling), and so even with the impressive LLJ strength as noted at SGF at 04 Z, you probably struggle to get much better than 600 SRH, and probably more like 400-500, which is still near the top of the significant tornado range of values.


Glen

 

[Evan Bookbinder]

Glen,

I certainly couldn't argue for more than 1KM, not only from SGFs sounding 2 hours later, but visual evidence of the supercell base at dusk and other data (RUC) that showed an equally low LFC and dwpt values which really tanked above that shallow moisture surge.

I don't have a sounding analysis program here worthy of John Hart's, but I'd be curious as to what values are achieved with 210@50 kts at 1km, a storm motion of 240@30 kts, and then anti-cyclonically curving the hodograph back to a sfc wind using several different values of between 10 and 40 knots with winds nearly due east. Given the sporadic tree damage laying from NE to SW we encoutered surveying the FFD region of the storm, I wouldn't be surprised to see the near surface winds channeled toward the higher end there.

A few chasers who have been privately conversing with me noted that this supercell had an extremely long and persistent inflow tail extending east of the storm, which not only justifies a mesonet ob that was to the S&E of the supercell, but in my opinion provides a better estimate of the near-surface inflow vector.

It's tough to eyeball from a hodograph, but I wouldn't be surprised to see this in the 600-700 range -- 300, 500, 700 it's MORE than enough.

Rich, our SOO says that she sent all the data down to the WDTB, so you guys should be able to access it from there.

Evan

 

[afischer]

If this discussion is to continue or if someone is going to try to construct a proxy sr-hodograph for this event, I believe the distinction needs to be made between whether you're constructing an ambient environmental sr-hodograph... or an sr-hodograph that is representative of the inflow sector of the storm (i.e., in really close proximity to it, where storm scale processes can obviously enhance low-level SRH). I'm sure an inflow-sector hodograph could be very interesting (Shamrock after-dark storm of 05/15/03 comes to mind, with ESE inflow winds gusting to near-severe levels)... but personally I think the ambient value would be of more use. I'm not familiar with what would even be a significant value of SRH in a particular level (e.g. 1km) if you're talking strictly inflow sector. (I haven't seen any observed hodographs in a tornadic supercell's inflow sector, or studies doing proxy soundings in a tornadic supercell's inflow sector).

I haven't reviewed the event closely, but my gut feeling is that there was nothing in the ambient environment itself that would favor surface winds backed to anything better than SSE. (As has been noted, the 1km SRH was still likely very favorable for significant tornado potential). IIRC, the synoptic warm front surged up to the KC metro area by afternoon. Pressure falls helped to back the surface flow in the warm sector (within which the storm ultimately tracked, along the northern edge of the low- to perhaps mid-50s Td's) between 21 and 00 UTC, which most certainly helped increase the 1km SRH (along with the strengthening 500-1000m agl flow per profilers). But again, unless we're talking about an inflow-sector hodograph very near the storm, I don't see why you'd wanna use anything more backed at the surface than 150 degrees or so. This corresponds fairly well with what I observed around Blue Mound while looking north (gusty winds generally at my back).

If mesonet obs indicated easterly winds and surface dewpoint depressions near zero immediately south of the FFD, then that'd be fine to use for your low-level hodograph and modified RUC sounding... but again, as long as you make the distinction that it's the inflow sector SRH and inflow sector MLLCLs etc, rather than the ambient SRH/MLLCLs.

My 2 cents.

 

[Evan Bookbinder]

Ultimately, I think we must realize that there is no "correct" answer and we're simply trying to get empirical proxies for things we simply can't measure yet. Moreover, the supercell updraft (tornado) is ingesting air from several different source regions...ambient, RFD, FFD, all of which are locally enhanced along the storm-scale boundaries produced by these colliding airstreams. I think we're all being ignorant to some degree by assuming that one of these is the greatest contribution to buoyancy/shear. All 3 must "play nice" so to speak to get this perfect balance we're after.

So in reality, I think maybe we're trying to too deeply classify things, where in reality there's a lot more subjectivity then saying "this storm had 528.34 J/kg of CAPE" or "it was 600 SRH, not 700". Rather, I think using rough proxies we can ascertain with some reasonable certainty whether a given environment supports supercells rooted in the boundary layer. If yes, and a supercell develops, how do the contributions from these various airstreams support tornadogenesis? To what extent can we measure/proxy them? Are these some rough values that lend toward weaker/stronger tornado potential? I think Rich Thompson and Jon Davies (just to name two), have made immense progress in this area in the past 3-5 years, and we can only hope that the funding for a Vortex II will ultimately help to answer many of the remaining questions.

More questions than answers I realize, but I'd hate to see us getting too caught up in "it was a surface wind of 152 degrees at 13 knots must have been right because that gives SRH value of XXX which produced the violent tornado". I'm equally guilty of this, when in reality the atmosphere doesn't care what the "value" is, just that the balance of moisture, lift, buoyancy and shear are manifested in such a way to support this "entity" that we're all after.

Some food for thought I guess.

Evan

 

[Reed Timmer]

I haven't seen much discussion on how INCREDIBLE this storm looked just before sunset. I don't know how this wall cloud did not produce...although some faint dust vorticies can occasionally be seen below the wall cloud/funnel.

I just finished a highlight clip of this event...which is dominated by the pre-sunset action.

http://youtube.com/watch?v=-FI1OYyI4Kg

 

[Evan Bookbinder]

That's pretty incredible Reed. Nicely done and I appreciate the slowdowns to highlight the lightning illumination of ol' Bertha. Out of curiosity, you guys appear to show absolutely no emotion during your video. What kind of boring chasers are you anyways?

In all seriousness, could you contact me privately? We'd like to obtain this video if possible for examples of nighttime spotting.

Evan