5/9/06 DISC: OK/TX

[BrandonWhittington]

Reports from local TV stations in Amarillo are stating that the northeast side of Childress, TX has substained significant damage. The high school has been highly damaged, gas lines are cut open, and large fires on the northern half of the town of Childress. Dumpers are scattered around and cars are flipped over on thier tops. Communication has been cut off and the town is still without power. Thoughts and prayers are with everyone in Childress as this event happend at the worst possible time of day.

 

[Jeff Snyder]

I'm slightly baffled by the way storms unfolded today... The cap on the 12z soundings was removed by mid afternoon, and the 0z soundings from OUN and DFW/FWD indicate an essentially uncapped enviroment east of the 'dryline' / confluence line that ran near I35. With CAPE being as high as it ever gets in this area (5000-6000 sbCAPE) and essentially dry-adiabatic lapse rates, I was expecting to see at least some very large hail reports. Looking through storm reports, there was one or two 2" hail reports, with the remainder >1.5"... In addition, I was not impressive at all by the reflectivity structure. Again, gargantuan CAPE , tons of it above the freezing level, and not much in the way of hail. We punched through the Coal co. storm about 20-30 before sunset en route to Atoka, and we didn't get any hail larger than pea size. There were several mesos on many of the storms in se OK, so that was okay. I know 500mb flow and deeplayer shear dropped quite a bit south of I40, but 1z RUC mesoanalysis indicated ~35kts 0-6km shear north of the Red River (near the Atoka/Coal co. storm), which was sufficient last week in western TX for some nice supercells. The conundrum we faced was this -- the better low-level flow was south (along Red River and into northern TX), while better flow aloft was nearer I40. The first few storms that developed in Hughes county looked like they'd move right along the OFB that was near and just south of I40. However, those storms moved a tad south of that OFB I think. I wasn't surprised to see the cell from Muskogee to the AR border look like it did, since the Fort Smith 88D VWP showed very nice low-level veering profile. Note also the very strong low-level shear and awesome hodograph curvature on the 0z OUN sounding (can't help but notice that the FWD sounding is completely uncapped too... amazing).

My thoughts? I guess parcel theory had a tough time in this environment. With such high dewpoints (and deep!), there was massive amounts of water in the updraft. With the extreme CAPE, there was likely huge amounts of water mass flux through the updraft (high water content + extraordinary updraft velocities per massive CAPE). Without stronger midlevel flow to help advect this moisture downstream / downshear (the FWD and OUN soudings look just fine, but I see that the 0z NAM initialized a local min in midlevel flow over se OK), water loading effects may have played a significant role in updraft intensity. I didn't have radar the whole time in the field, but my intermittent radar images from 5pm - 8pm indicated that the max reflectivities on most of the storms were <65 dBz, though the storm near Stuart did jump into the upper-60s for a brief time (this is on tilts 2-3 from KTLX, so it's above the ambient freezing level). VILs were high as one would expect, with rather vertical / erect updrafts and massive amounts of moisture available (remember, the Level III data REMOVES >55dbz echoes in the VIL calculation, in an attempt to remove hail contamination, thus the reason why VIL is NOT a good hail indicator!). Given the lapse rates and instability available, I was expecting some very high reflectivity cores owing to the presence of hail the size of Geo metros. I guess this was far from the case...

It was interesting to see how quickly rotation developed in many of the storms, likely a product of the incredible vertical acceleration (courtesy of the insane CAPE) and associated stretching of vertical vorticity (that had been tilted by significant gradients in vertical velocity, as we expect and assume near strong updrafts). RUC mesoanalysis indicated that the low-level shear was just fine (200 0-1km SRH ahead of the Atoka/Coal co. storm), so I was surprised to see that it appeared rather outflowish by the time we got to it after 8pm. High boundary layer mean RH and 15-20kts 0-3km shear should have helped keep cold pools in check today as well. I suppose the shear may not have picked up enough until after we had numerous updrafts nw of McAlester, by which time we already had begun the congealing process. Once cold pools from different storms consolidate, it's difficult to reverse the trend (in other words, difficult to go from MCS / quasi-linear structure back to discrete activity).

I'm just kind of writing all my random thoughts about today... I guess it ultimately came down to numerous cell mergers and many cell interactions... The cell in Coal co. remained nearly stationary for a while, and the very high rainfall efficiencies were evident as we drove around that area (lots of flooded yards and ditches, some significant ponding on the road, etc).

Oddly enough, there were many questions about initiation in the se OK target, but many assumed supercells were a guarantee given sufficient deeplayer shear and extraordinary CAPE. Meanwhile, many (myself included) blew off the panhandle play, thinking that would be a sure bet for convection, but likely MCS in mode. As it turns out, the se OK activity had occassional supercell structure, but was largely MCS in nature (esp by 7:30-8). Meanwhile, convection remained discrete in the panhandles, allowing for several nice supercells. Ugh.

 

[Blake Michaleski]

My thoughts? I guess parcel theory had a tough time in this environment. [/b]

you said it right there, it sure doesn't always work liek you'd like it to.

I was nowcasting for Erik Perozo who was in SE OK. I watched the entire event from initioation untill they called it off. I too was baffled at the time as to why these things didnt just explode into massive raging supercells. The water loading of the updraft makes perfect sense considering how deep the moist layer was.

Good analysis Jeff.

 

[Jonathan Whitehead]

on the same topic as what Jeff was discussing about how things unfolded today....

MOVED FROM 'NOW'

I must say for a day that was looking like absolute crap tornado/shear wise (which is why i didnt chase), i am really impressed by all the wall clouds/funnel reports not counting the touchdowns. Cells were able to remain discrete a lot more than I thught they would. I am also surprised by how several of the cells were able to exhibit decent low level rotation, further producing funnels. I was certainly expecting basically a repeat of April 1 where things just go MCS right from the get go. Guess it really proves how significant a play outflow boundaries can be.
Of course I havent even mention to cells out west. THOSE were the ones that were supposed to be MCS from the start. And what happens, the most unlikely of scenarios, a cell hooks and starts to rotate. And this stuff is post-frontal, hell, SPC only had panhandle region in 2% tornado. Im just amazed how things have just totally fallen off the table. But I will say, if I had this day to do over again, I still would not have gone out due to distance (=gas $$) and terrain.


Note on that Anna cell, I believe thats the closest tornado to the metroplex since the Ft. Worth tornado several years back.

 

[Kenny Drake]

I think the main issue with the storms over SE OK has to do with the lack of a well-defined dry-line. Without the dry air intrusion into the western side of the cells water loading becomes an issue as Jeff mentioned. Moisture is great, but too much adds a lot of weight to the updraft effectively decreasing updraft speed and helping outflowish situations. If I remember Mesonet observations from earlier today, the dryline dropped Td's from the upper 60s/low 70s to mid 50s to lower 60s and the gradient was not sharp by any means. This is why I think the cells over the panhandle were able to remain discrete and sustain themselves longer -- they had sufficient moisture and the dry air inflow from the SW/W. Whats even more interesting is that these cells fired well behind the stationary front. Observations from this morning showed strong northerly advection stretching all the way into central TX.
Synoptically, the main difference I see between our classic setups is the 500mb trough digging over the midwest, and not the SW. The main difference I see out of this is the location of todays severe weather relative to the trough location. Normally, I'm used to seeing a surface low develop on the north exit region of a trough. Today the whole chase area (OK/TX) was on the south side, almost over the trough axis. In basic theory, OK was over an upper air convergence region of the jet max associated with the trough (today). Thats what I make of today without complicating it to where I can't think anymore.

 

[Jonathan Whitehead]

Synoptically, the main difference I see between our classic setups is the 500mb trough digging over the midwest, and not the SW. The main difference I see out of this is the location of todays severe weather relative to the trough location. Normally, I'm used to seeing a surface low develop on the north exit region of a trough. Today the whole chase area (OK/TX) was on the south side, almost over the trough axis. In basic theory, OK was over an upper air convergence region of the jet max associated with the trough (today). Thats what I make of today without complicating it to where I can't think anymore.
[/b]

three words: right entrance region

 

[Kenny Drake]

three words: right entrance region[/b]

Just to clarify, you mean left? generally NE side of jet streak has the most divergence, SE exit region has directional convergence. SW entrance region is marginally divergent and NW is speed and directional convergent. I could easily be wrong as I'm tired, I'll look at it again in the morning as I might actually be tested on this on Friday.

 

[Jeff Snyder]

Just to clarify, you mean left? generally NE side of jet streak has the most divergence, SE exit region has directional convergence. SW entrance region is marginally divergent and NW is speed and directional convergent. I could easily be wrong as I'm tired, I'll look at it again in the morning as I might actually be tested on this on Friday.
[/b]

Transverse circulation and ageostrophic motions associated with jet streaks result in upper-level divergence in the right-entrance and left-exit region of upper-level jet streaks, and upperlevel convergence in the left-entrance and right-exit region of upper-level jet streaks. The right-entrance region of the jet streak across KS began to affect eastern OK likely after 0z, though that area also was in the left-entrance region of the anticyclonically-curved jet streak in the subtropical jet in TX. The 0z NAM initialization indicates that the jet streak in KS propagated northeastward in time, such that the right-entrance region associated with that jet streak, and associated upper-level divergence and upward motion, was over eastern OK after 0z.

Additional upper-level convergence or divergence associated with the larger-scale flow may enhance or detract from the div. or convergence associated with the embedded jet streak.

 

[Kiel Ortega]

I think the main issue with the storms over SE OK has to do with the lack of a well-defined dry-line. Without the dry air intrusion into the western side of the cells water loading becomes an issue as Jeff mentioned.
[/b]

I don't think the dryline mixing in dry air on cells has much do with anything--cells need to come off the dryline to do something. Dry air above the boundary layer does it. However, looking at the 10/00Z OUN/FWD soundings, compared to 09/12Z OUN/FWD soundings, the amount of dry air above the BL did decrease...near OUN and FWD, there was lots of cumulus going up, which probably accounts for the decrease.

Jeff the only problem I see with what you are saying is that if there was extreme CAPE leading to high mositure fluxes in the updraft, how come most of the updrafts were fairly skinny (especially when the midlevel RH probably increased due to all the cumulus before the show--per soundings and some guessing)? I know the storm Bryan and I watched fire from Wolf, OK was not very broad at all (I don't know what happened down south). However, it had continuous, skinny updrafts develop on it's flank and it never did anything. Given the lack of upper level support (Jeff, you mentioned at SEC how the winds seem to split us; and I think the UA support came late anyways) and an uncapped surface, it was up to the surface to form the storms. From what I heard and can kinda see on the OK Mesonet meteograms, the east side of the boundary sagged south while the west side stayed up near I40. The first storms to fire were near I40 (where the dryline and outlfow boundary met), while the southern storm fired much later (just the dryline). Since it was up to the surface for storms to get going, the slow motions probably hurt too. Per satellite observations, it looks like that dryline in OK took a surge towards 00Z. That led to all those cells firing south and mergering together near Atoka (and points north I would assume). So lack of UA support, lots of moisture, slow winds and you get what we got. So either take this complicated (probably wrong ) explanation or "blame it on the rain yeah, yeah" LOL

 

[Dan Dawson]

I too was a little surprised to see how the updrafts were struggling in SE OK, at least initially. Basically, I think both Jeff and Kiel are on the right track. The initial storm updrafts were skinny and pulsed quite a bit, and you could literally visually see the entrainment of the drier midlevel air into their updrafts, so that by the time they reached the upper levels of the troposphere, they had lost much of their buoyancy, and were clearly not realizing the full CAPE. The water loading effect definitely could have come into play in this as well. Essentially, I think that at least initially, lack of sustained surface convergence/forcing for large-scale ascent, and some significant cap possibly still remaining in the areas surrounding the initial storm updrafts, both contributed to the struggling updrafts we saw early on. Once you do get a decent cluster of updrafts, they begin to insulate themselves somewhat from mixing of environmental air, and the developing storm can finally begin to take off. Enhanced surface convergence from the development of a downdraft, as well as favorable pressure gradient forces due to the presence of a rotating updraft/interaction of the updraft with the shear, also contribute to this. Basically, this is what we saw after a while, once storms finally started to get sustained (plume-like, not bubble-like) updrafts. After that, I think our problem was too many storms and storm interactions, and perhaps that weakness in the mid-level flow that Jeff mentioned.

 

[Gabe Garfield]

Personally, I'm still convinced that yesterday's failure in SE OK had more to do with the lack of organized rotation within the storms. As many know, rotation within a storm enhances the upward vertical velocity due to vertical pressure perturbations. I personally believe that high CAPE environments (such as yesterday's) can only support minimally severe hail without strong rotation. Then again, I've seen squall lines with bigger hail, so who knows (perhaps that was associated with an embedded supercell?).

Based on the storm behavior (i.e. multiple splitting supercells), it seems likely that we were dealing with straight line hodographs (unlike storms further west that obviously benefittedfrom clockwise curvature in the hodograph). In fact there was one storm that I saw on radar just north of I-40 that had an anticyclonic hook echo! Thus, I believe that storms were struggling for an identity for the majority of their existence. Being fed equal amounts of cyclonic and anticyclonic streamwise vorticity doesn't do much to establish one type of circulation over the other.

On another note, I'm absolutely amazed that there were significant tornadic supercells with ENE surface winds in the Southern Plains! Absolutely unreal!

Gabe

 

[Jeff Snyder]

Well, as I thought I would, I forgot to grab a RUC 0z 0hr sounding last night.. I wanted to see what the RUC-analyzed hodographs looked like in se OK. With southeastern sfc flow, the hodograph was pretty straight I would imagine (veering with height, but straightline shear), and that's probably why we did see right and left-splits. However, as it happens, as the right-split moves right of the mean shear, it develops a storm-relative veering wind profile, thereby developing cyclonic streamwise vorticity. Conversely, the left-split moving to the left of the deeplayer / mean shear vector on a straighline hodograph yields storm-relative backing vertical wind profile, and associated anticylonic streamwise vorticity.

However, the RUC showed 150-250+ 0-1km SRH in se OK by 0z, indicative of significant veering shear profile given the relatively slow storm motions yesterday (if flow was stronger, and storm motion more deviant, you could get high SRH even with a straight-line hodograph... Yesterday, however, flow wasn't very strong, which tells me that an increase in SRH likely had more to with hodograph curvature than anything else). This would argue that low-level shear was not the issue. Of course, this was after cold pools started to interact and merge, so I'm not sure if it was a 'too late' situation.

I do wonder what determines the size of the thermal/plume, however. I would think it'd have to do with the depth of moisture or depth of the boundary layer, and perhaps the strength and distribution of CINH. Rgardless, it seems relatively common for the 'first attempts' to be skinny updrafts that act more like thermals than plumes (spatially and temporally discontinuous vs. spatially and temporally continuous), which is why I tend to look for 'clumping cumulus' when trying to find the storm I think will take off and hold its own. I've seen better looking supercells on days with drier midlevels, so I'm not sure... I'd imagine cloud-edge lateral entrainment would be present, but I wouldn't think it'd be abnormally intense given that we didn't really have very strong midlevel flow impinging upon the side of the updraft tower. Perhaps the CAPE was so intense that it created eddies along the side of the updraft, enhancing entrainment of drier midlevel air? Then again, this is what we see on the leading edge of a thermal or plume, but not after a plume is established... I would have thought that once a storm did take off, despite the initially weak surface flow, low-level convergence at the base of the updraft (courtesy of continuity, which states that, at the ground where w=0, vertical acceleration must be accompanied with convergence -- dw/dz = -(du/dx+dv/dy) = - (divergence) = convergence) would act to increase inflow into the storm. I mean, we sat in Stuart to the east of a meso (west of the meso just nw of McAlester), and there was almost zero inflow. Of course, the main inflow may have been to our southwest, but I neved like being in the inflow area of a storm (at least not the outflow) and feel light winds. Maybe the CAPE was so extreme that the compensating subsidence outside the updraft was also quite intense, yielding a skinnier updraft? LOL I duno, I'm grasping at straws for that one...

 

[JP Santiago]

NBC 5 has airborne video of the damage on their main page: http://www.nbc5i.com/index.html

 

[Eddie Natenberg]

OK im going to take a stab at this one.

First off did we have too much cape? Its a question I've asked myself after seeing the BRN formulation over and over again for the last week. Even though we had lots of stretching of vertical vorticity, was the CAPE too strong for moderate amounts of low level vorticity (and even less before the LLJ kicked in). This is one possible explanation why the storms in SW Oklahoma became discrete while the storms to the SE were turning mulitcellish with imbedded mesos. I noticed that all the storms we were on in SE Oklahoma had great mid level structure with a massive RFD plowing underneath the meso. I can't even count how many unorganized elevated funnels we saw in outflow winds (at least they were fun to watch). Just a thought :unsure: .

Eddie

EDIT:

sounding output from 00z

72249 FWD Ft Worth Observations at 00Z 10 May 2006
+Bulk Richardson Number: 63.58

72355 FSI Fort Sill Observations at 00Z 10 May 2006
+Bulk Richardson Number: 16.11

hmmmmmm...

 

[Dan Chaffee]

For a storm structure photographer, I struck pay-dirt on May 9 in the southeastern TX Panhandle. [/b]

Definitely a winner, Mike!
Could you see anti-cyclonic rotation in the new updraft to the NW of the main cell on the first image?

DC