Let me respond to a few comments about why the southeast OK storms weren't massive supercells.
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. [/b]
I'm guessing the idea here is getting too much precipitation loading in an updraft. Unfortunately, the observations to date don't support an easy relationship between water loading and inflow moisture amounts. In a really fat CAPE profile like Tuesday, any updraft realizing a decent fraction of that CAPE would have such a strong updraft that decent size hydrometeors wouldn't form until nearly anvil level. That's one of the reasons a BWER forms on radar. Low-level boundary moisture also does not seem to be related to supercell type. Take a look at Erik N. Rasmussen and Jerry M. Straka. 1998: Variations in Supercell Morphology. Part I: Observations of the Role of Upper-Level Storm-Relative Flow. Monthly Weather Review: Vol. 126, No. 9, pp. 2406–2421. Think Mulvane, KS 2004 Td=77F, OKC - June 13, 1998 Td=80F, Plainfield, IL 1989 - Td=81F. No, give me huge CAPE and lots of moisture.
Regarding whether the boundary was too ill defined, it's not an adequate explanation. The last recorded F5 producing tornadic supercell developed developed on a horizontal convective roll and not even the dryline. See
http://ams.confex.com/ams/htsearch.cgi?act...override=&pge=2
On May 3, the hypothesis was that if the surface forcing was stronger, a squal line could've formed instead. Maybe it would've happened but I'm not sure.
Kiel responded
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).[/b]
Dan agrees too.
Good question here. The storms started out skinny and that would subject them to dry air entrainment aloft. The storm I started seeing east of Wolf certainly didn't realize anything more than 1000 J/Kg. But the cell firing on the flank of the MLC storm to be started realizing some real buoyancy but it got absorbed by the mass of congealing cores.
Gabe pines
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). deletia. 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.[/b]
I'm a bit cool on this. Sure, I'd like to have a big clockwise turning hodograph but we could've at least had decent supercells with a straight line hodograph. Perhaps it was straight line but with only a 30kt 0-6km bulk shear as Jeff alludes to? The Purcell profile winds in the lowest 3 km were pretty weak. Maybe some of that weakness extended over to the east. BTW, there was a great example of a dominant left mover on the storm just south of the Childress supercell. Did anyone notice how that left mover passed just in front of the right mover just prior to reaching CDS?
Speaking of Jeff's response, I'm just as confused as you. In my experience, big CAPE gives you big potential for a storm to modulate the low-level hodograph even more than smaller CAPE, however bigger shear also provides this benefit. I think if you have adequate shear in the lowest 6 km, a big CAPE storm will generate a large hodograph right down to the surface. A great example is Spencer, SD on 30 May 1998. There was near zero 0-3 km helicity but great deep shear and huge CAPE of 5000 j/kg. Chasers reported ssustained inflow of 30 kts. I believe that some chasers felt a similar ramping inflow ahead of Anna TX Tuesday night. Why was the Anna TX storm so different from MLC or Atoka?
Eddie's response
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.[/b]
BRN was developed by Weisman and coauthors to explain storm type spectrum in idealized thermal bubble initiated model storms with no ice microphysics in the early 1980's. Later, Dave Stensrud at NSSL found the paramter did little to differentiate supercell from nonsupercells with real data. SPC stopped using the concept after too many busted forecasts on high CAPE days. Here's some great huge BRN cases: Mulvane, KS 12 June 2004, Jarrell TX 1997, The day before Jarrell in eastern OK of 1997. Speaking of the day before Jarrell, there was an event of similar CAPE, similar weak surface winds but nice deep layer shear. Guess what, there were numerous tornadoes.
I'll throw my 2 cents into the fire. I bet if the storms initiated in a more isolated manner, there would've been better supercells. However, the tornado failure rate would've still been high. I believe that big CAPE but poor 0-1 km shear days are recipes for high false alarms but with the peak potential being wedges. But with so many storms clumping together, there was too much interstorm seeding and that leads to reduced hail and increased rainfall rates. There were some supercell structures in that mess but not ones with iincredibly strong updrafts of the likes of Spencer. It is quite likely more than one problem existed on Tuesday. If there was stronger shear, then maybe the storms would've isolated themselves as weaker updrafts would've been blown away. If there was stronger low-level shear, maybe there would've been more rain wrapped tornadoes. I'm not sure.
Perhaps all this post mortem speculation is not the right way to analyze the failure modes. There's too many untestable hypothesis. When I make a forecast, I think of failure scenarios and hypothesize why it would fail. If the event fails, at least I cannot reject my hypothesis. Maybe one of the forecasted failure scenarios is the right one for the day.
