8/19/09 DISC: IL/MN/OK/KS

[Paul Hadfield]

Due to having no data access and not wanting to take chances with the line producing numerous embedded supercells, I stayed at home located NW Decatur IL. It worked out for the best being that I was in direct line for the cell to produce at Loami IL. This storm had a couplet for much of its life and in reviewing radar data, seemed to collapse into a huge downburst right before entering the city. Ideally I would have preferred to be out in the field but made due with what I was dealt. I'll post a blog later but in the meantime, enjoy the following clip.

http://www.youtube.com/watch?v=MfxNv1EwGFE

 

[CZandbergen]

8/19/2009 DISC: OK

I am sitting here scratching my head tonight wondering what went wrong with the setup today? You can take a look at the forecast thread to see what we all thought should have been, but it clearly didn't happen. I wasn't alone with this one as there were many chasers and news teams around the Enid area hanging out waiting for the show that never happened.

After getting home this evening I took a look at the 0Z soundings and I am still confused as to why nothing significant went up. From the looks of the towers going up this evening there were issues breaking and sustaining a break through of the cap. Also, the updrafts were really weak from what I could see. Looking at the soundings, the H7 temp at OUN was 9C but the sounding from DDC was 15C. The SGF sounding was 1C and that is closer to where the sustained convection was in SC/SE KS. I would have thought 9C was a reasonable cap for August, but maybe the cap was closer to the 15C from the DDC sounding.

Everything on the ground pointed to a great setup. How often do we get nice backed winds in August? Anyway, I would love to hear anyone thoughts on the setup and what went wrong.

 

[Chuck Hurley]

The Loami storm turned into a mess quickly. I was in the path and had a lightning strike the power lines in the alley directly behind my house. Amazing how fast the sound traveled from 50 feet away. The rain came and just dumped on us with some pea size hail mixed in. At that point I was without radar so had to call a buddy to give me updates. The storm was very intense and the core punched me I really didn't appreciate that punch from mama N.

 

[Jeff Snyder]

I figured a proximity sounding would show some CINH. However, look at the 00z LMN sounding, which was not too far on the cool side of the OFB:

IIRC, there was a thread not too long back about parcel theory, and the limitations thereof. This is another good example of how a single sounding and parcel theory doesn't explain the whole story... For the most part, the sounding represents an environment that is uncapped for a mean-layer parcel (and definately uncapped for a surface parcel), and the hodograph looks pretty good (though not much shear in the 4-6 km AGL layer). The SiggyTor and SCP numbers support the reason why many of us were up in that part of the state. Despite what must have been pretty strong surface convergence west of END (per OK Mesonet data) and very little to no cap, we still didn't really see sustained intense convection. I had been worried about perhaps some drier air off the sfc mixing out some of the sfc moisture as low-level parcels rose to the LFC, but the LMN sounding above certainly doesn't show that. All day, though, the updrafts and Tcu/Cb appeared quite skinny, and the bases were either ragged or quite diffuse / "soft" and laminar (which usually represents parcels being forced through a stable layer).

That sounding is the best looking sounding I've seen in this state this time of year, so it's disappointing to see that it was essentially a bust.

 

[CZandbergen]

Jeff,

It was good to meet you again and lament with you this evening as we watched everything peter out. As I mentioned when we were sitting on the side of the road I wonder if the issue was the upper level winds. In the sounding you posted there is pretty much zero directional shear from 2km up. The towers seemed to go up and then have the tops blown off from the west. It is interesting that the sup numbers were through the roof per the SPC historical readings but it failed to produce. I am left wondering if we had a great May setup at the surface to 2km and then nothing to support it from there up.

My only concern with the setup was the weak hodographs from H7 up. Maybe that is what did us in today. It does bear thinking about in the future. I think a null case teaches us as much or more than an outbreak...

 

[Jeff Passner]

I did not get a chance to watch this carefully, but I look at the sounding and see +12C at 680 hPa. There looks like there was about 3C warming at both 850 and 700 hPa. That layer at 660 hPa warmed 4C during the day... I just think subsidence was tough to deal with. There was not significant advection of vorticity and convergence at the surface was localized and not strong enough to overcome the warming aloft. Otherwise, incredible shear for August... Just an incomplete day.

 

[Mike Smith]

I was in southeast Kansas (far southeast Butler Co.) and did see some small funnels, but they never could get their act together.

I am surprised nothing happened. I thought it was an amazingly good situation for late August. There was a weak short wave moving east from the High Plains as a trigger, plus the threat area was in the right rear quadrant of the wind max at 250mb. There was plenty of instability and the low levels looked great.

Here is a hunch that has no scientific (in the sense of objective proof) backing: Some years the airmass "likes" to rotate more than others.

In the late 1980's, superb hooks (pre-Doppler) would be warned on and nothing. From 1990-1992, it seemed every storm in south central Kansas produced a tornado, even those (Hesston, for one) that never produced a well-defined hook over significant parts of its path.

In 2003, everything rotated. This year, zip.

On a number of occasions, Erik Rasmussen and I have discussed that there is something that is eluding us -- that we are not measuring or capturing -- that will hold a key that will allow us to much improve the accuracy of tornado warnings.

 

[afischer]

Just glancing at this a bit after sleeping through the event, and am wondering if weak-ish convergence could have played a role. IIRC, the obs at Alva and Watonga (AVK and JWG) tend to be suspect... I recall seeing several times where I questioned not only the T/Td ob at Watonga (JWG) but also the wind direction. Watonga's wind seemed more strongly veered than adjacent sites to the W/S... ignore that ob, and the overall magnitude of wind convergence is suggested to be rather modest (particularly 23Z and beyond as the outflow pool over northeastern OK continued to modify)... so I wonder if that played a role. Maybe if the slightly stronger southwesterlies in the deeply mixed hot prod nosing up toward Lawton could have butted up against the boundary, sustained convection would have faired better. The sounding posted above is certainly very nice, with 100 mb dewpoints around 72F, a deep boundary layer, and seasonably cool capping above the boundary layer all contributing to very strong instability and strong low-level CAPE. It's also interesting that mid-level flow remained cyclonic over the area through 00Z--though I wonder if any shortwave trofiness in the base of the trof may have been translating away from the area by then (which would be a problem, and might explain why the bulk of the activity developed in SC/SE KS).

Re: the above comment... I don't see any warming on the Lamont OK RAOB between 18-00Z, with the exception of the sfc-1 km layer. Most levels between 1 km agl and the trop seem to have cooled around 1°C during that time... even moreso in the 500-300 mb layer.

 

[Jeff Passner]

There was significant warming on the OKC sounding between 1200 UTC and 0000 UTC. While the OKC sounding was not in the exact area of interest, it probably warmed just as much below 600 hPa in northern Oklahoma also. The weak surface convergence also did not help.

 

[Mike Smith]

I gave this a little more thought overnight. Take a look at the tornado parameters on the LMN sounding (above). They are higher than the respective values for Greensburg. These values were consistent with what the 18Z RUC from yesterday were predicting for 23Z, so they were not out of line. Perhaps there was some mid-level warming in the area the balloon did not sample, but it is not like a cap killed convection. There were severe thunderstorms 60 miles northeast of the sounding in the same air mass.

We are, understandably, picking apart surface obs and layers that dried (for example) but the fact is that these values of "off the chart" -- meaning if the sounding did not perfectly capture the air mass, the lowering of the SIG TOR to, say, a value of 6 would still be around the value of Greensburg.

So, given LMN sounding was consistent with that the RUC was forecasting for northern Oklahoma / southern Kansas, I think it would be more worthwhile to ask "what is wrong with the index" (and what is wrong with our understanding of the tornadic environment) more than "what is wrong with the sounding." Clearly, there is something eluding us.

 

[Jeff Passner]

Of course something is eluding us... It probably always will. I found the day interesting even if I was not going to chase it and it did look good to me but I also had some concerns about the cap, especially early in the afternoon. Granted, there were storms 60-100 miles away, but this is not that unusual. It happens in the middle of the traditional storm season too. The question should become: Why did the storms initiate in SE Kansas and not NW Oklahoma or northcentral Oklahoma? I just think it's a matter of an ability to overcome the subsidence. If I can find some time I'm going to capture the Nam-218 fields from 1800 UTC and use them to initialize a 1-km WRF and then look at the vertical motion forecasts and things of that nature. I'm just a little curious if the increase in resolution and short-term forecast can give some clues. Models can sometimes fill in the gaps for the things we can not actually observe.

 

[Mike Smith]

Jeff,

You post valid questions regarding development in northern Oklahoma. However, thunderstorms did develop in Cowley Co., KS -- not far away from the sounding site -- that went severe. In the southern Flint Hills the cap was not an issue.

To me, the question is: Why did supercell thunderstorms that produced large hail not produce a tornado in an environment with 5000+j of CAPE, a more than acceptable hodograph, 0-1km helicity of 300+, etc.? SPC issued a tornado watch. The SIG TOR (meaning ≥F2) indices were far above the thresholds.

Since the 00Z LMN sounding was consistent with what was forecast for the area at the time of the sounding, it seems unlikely the values produced from the radiosonde were unrepresentative of the surrounding environment.

So, if those values were representative, there is something wrong with our theoretical understanding and/or with the indices, at least as they pertained to this case.

Mike

 

[Mike Umscheid]

Yesterday was indeed interesting. After the redbox conf call with SPC at work, shift was over and I left DDC at about 4:15pm and headed down to the clumping Cu field in Woods/Alfalfa county. When I first left, a nice hard tower was evident distant southeast and when I looked at radar and saw the blips wayyy the hell southeast close to Enid, I thought this was a fool's errand. Got gas in Greensburg and contemplated heading home. I then noticed some agitated cumulus to my southwest. Observations showed southwest winds all around northwest OK... yet dewpoints were in the 65 to 67 degree range. Even with a southwest surface wind, there was still excellent deep layer shear across NW OK with the impinging upper jet streak from the northwest. It became clear as I was driving south toward Hwy 64 that the OFB towers were just not doing it. I was rather surprised, like the rest of you, that I didn't see atom-bomb city going on southeast. I wonder if there was a mesoscale gradient in CINH there that was just too much for the Enid towers as they were advected downstream to the east? Were these towers/plumes moving east or southeast? If they were moving due east, they would have crossed the boundary at a sharper angle and succumbed to the CINH faster... just not enough time to get that deep sustained moist convection process "jump started".

These were the things that were actually running through my mind as I was watching this unfold from a distance to my southeast. Meanwhile, to my southwest, the boundary layer was deeper with lower 0-3km static stability and thus easier to "jump start" deep, moist convection. It's all about initiation, and the direction of motion of towers once they initiate. It just seemed to me that once plumes went up, they crossed the boundary and the strongly backed winds were doing a number on the "jump starting" process. Nice backed easterly winds are great once you have a well-established storm, obviously. What if the towers formed 20 miles farther west...such that they had more time to accumulate growth...before interacting with the higher CINH easterly flow east of the OFB? It could have been a much different story perhaps. I'm just thinking out loud here.

When I got to Hwy 64, I drove west and thought that I could get a good storm going around Harper-Ellis County given the uniform lower static stability in the lower troposphere + CAPE still around 3000 J/kg. 800 to 1000 foot higher elevation also helps in this department for convective initiation... which is why I usually favor farther west for storm initiation. I've seen this song and dance before -- fantastic looking soundings, good convergence, parcel theory suggesting CINH < 25 Joules... yet still nothing. In almost all these cases, there seems to be too sharp of a potential temperature gradient with initial storm motion vectors taking initial plumes into the cooler pot temps too quickly...and you just end up with anorexia.

Oh yeah, the northwest of Woodward storms were pretty photogenic. Saw a wall cloud at sunset northwest of Woodward, some incredible crepuscular rays radiating through a storm tower (the soon to be Woodward supercell)... there were actually two side-by-side initially. I'll get some images uploaded soon.

Regarding the Cowley county storm: Was this storm *truly* surface-based? I need some convincing this was a surface-based storm... temperatures southeast of ICT were around 80. Looking back at some of the NAM12/RUC40 data, north-central OK through southeast KS was amidst very strong 900-800mb warm advection. I believe the Cowley county storm was initiated through very strong warm advection and not from boundary layer convergence -- and thus was the likely reason it did not "produce".

 

[mike scantlin]

My vote goes to the lack of directional shear above 2km. Not just the lack of shear, but the orientation of the shear from 2km up. The storms had an awkward 'tilt' to them on radar, and you could see it in person as well. As soon as the storm really got going, you could tell it couldn't breathe, as the updraft/meso region was NW of the downdraft/precip core. As time went on, the storm was producing some nickel hail, but the updraft was displaced from the downdraft by miles, literally.(radar image attached, video grabs attached later...) I'm not sure what kind of shear profile would cause this. I didn't do much in the way of forecasting yesterday, as all the quick-look parameters were off the charts. Even the Sups out near Woodward had the weird tilted orientation to them. I would love to hear(and see) what Mike U has to say about those storms and why they crapped out in an area of Greensburg parameters.

 

[Jon Davies]

I gave this a little more thought overnight. Take a look at the tornado parameters on the LMN sounding (above). They are higher than the respective values for Greensburg. These values were consistent with what the 18Z RUC from yesterday were predicting for 23Z, so they were not out of line.

Let's get away from point soundings and "indices" for a moment, and look at the bigger picture, particularly from satellite.

Go look at a visible satellite loop over KS-OK spanning Wed p.m. The outflow boundary over central into northwest OK from a large area of morning convection stayed essentially stationary through the afternoon. Notice that there was a definite and consistent absence of boundary-layer clouds northeast of the boundary south of the Kansas border, suggesting the presence of subsidence or some inhibiting force over that area. When updrafts went up along the boundary at late afternoon in the Enid area, the upper flow carried them over to the "wrong" side of the boundary, and they dissipated as they moved into what appeared to be more subsident clear air from satellite. With already warm 700 mb temps (12-13 C), and the orientation of the boundary relative to storm motion, the updrafts appeared to be fighting an uphill battle, which they lost. Had the updraft/storm motion been parallel to the boundary (ala 5/24/08), rather than crossing into the apparently "subsident" air, it's hard to say, but yesterday's results might have been different in northern OK.

It's also important to note that the storms near dark that went up southeast of Wichita formed in an area around the northwest side of the Oklahoma subsidence (small bubble high?) where boundary-layer clouds and "agitation" were visible moving eastward during the late afternoon and early evening. So, looking at visible "subsidence" characteristics on satellite, this portion of the air mass appeared different.

Although yesterday's Lamont profile may have had some similarities to 5/4/07 Greensburg regarding "index values", the synoptic settings were obviously _quite different_. In the Greensburg situation, massive warm-moist advection was taking place over a large area in advance of a huge long wave trough, and 700 mb temps were cooler (around 8 C rather than 12-13 C). Yesterday, while there was convergence and moisture pooling along the local outflow boundary over n-c OK, the boundary wasn't coming back northeast, and clearly, even with an atypically strong upper trough for August, the dynamics weren't nearly as strong and were oriented quite differently.

Point soundings don't highlight subsidence and inhibiting issues that we don't really know how to measure. There are alot of soundings out there with no CIN and no convection.

Jon Davies