STORM2K

In this (time sensitive) image, one can see a large scale vort max embedded within the convection in E Central Arkansas, and associated trailing squall line extending SW to NE ... supercells are developing rapidly just out ahead of the main squall line, with embedded bow echos/segments, and LEWPS (line echo wave patterns) ...



tremendous divergence aloft continues to enhance the convergence at the SFC as depicted by anvil level winds ...



supercell composite yielding values as high as 8-10 in SW LA, and SE TX ... with significant tornado greater than 4 in a large area, with bullseye's exceeding 7 ...



Craven SigSvr Parameter (described by SPC in Norman, OK) ...

The simple product of 100mb MLCAPE and 0-6km magnitude of the vector difference (m/s; often referred to as "deep layer shear") accounts for the compensation between instability and shear magnitude. Using a database of about 60,000 soundings, the majority of significant severe events (2+ inch hail, 65+ knot winds, F2+ tornadoes) occur when the product exceeds 20,000 m3/s3.

The index is formulated as follows:

C = (mlCAPE J/kg) * (SHR6 m/s)

For example, a 0-6-km shear of 40 knots and CAPE of 3000 J/kg results in a Craven SigSvr index of 60,000. Units are scaled to the nearest 1000 on the web plot.

And tonight we have a widespread area of >20 (or 20,000 m3/s3) ... and some bullseyes exceeding 60 ... (60,000 m3/s3.) ...



It will only continue to get uglier ... and if the nocturnal LLJ gets even more involved, potential F4's and a OUTSIDE POSSIBILITY of an F5 downstream towards E LA/C MS ...

SF

Does it look like this could Spread east Thru the night and into tomorrow afternoon.

Wnghs2007 wrote:Does it look like this could Spread east Thru the night and into tomorrow afternoon.

That's the point ... especially bad in MS later tonight ... as the best dynamics move NE, the threat will gradually diminish points south, although, an ongoing squall line should continue and with any sufficient insolation out ahead of the squall line should serve to intensify the line down south ...

Tornadoes are still possible tomorrow but shouldn't be as widespread given the bit of decoupling of the best parameters ... but damaging winds will eventually become the primary threat ... especially along the Gulf Coast and again towards TN/KY/OH where the best dynamics lie ...

SF

My weather radio is on alert - I'm already prepared
to be in for a long ride, tonight, especially closer
to early morning! Thanks, SF!

The MCV over Arkansas could mean big trouble tomorrow afternoon as it moves towards eastern TN/KY and perhaps the Carolinas. The models aren't going to pick it out, but it is in a mid/upper level environment very much conducive for surface low development underneath it. This will be a surface low sepearate from the rapidly deepening one over the mid-MS and OH Valleys. That means the winds out ahead of it will be from the south or southeast (as opposed to SW) and supercells are likely tomorrow if it stays together (which it should given upper level dynamics and the extremely moist environment). This is a scenario similar to what happened on July 21, 2003 over PA and upstate NY. A derecho or good ole squall will likely form out ahead of it. This will all be in addition to the convection associated with the warm front, cold front and a pre-frontal trough (sort of similar to the line south of the vort max over Arkansas with all the tornadoes now.

F5?? I thought only the Plains states got those . Scary stuff. I would not be paid a million dollars to be within a mile of an F5.

Bit concerned about the potential backing flow with the associated MCV ... one of things, however, MIGHT be a lack of insolation tomorrow across the aforementioned regions. BUT any sufficient heating/breaks with sun would serve to destabilize the atmosphere, quite rapidly, with a few hours of sun ...

So far all the storms have stayed north of south Louisiana, but there has been numerous supercells traversing central LA. I'm starting to think we won't really see any supercells this far south but the squall line forming west of Houston will be downright nasty by the time it gets here.

PTrackerLA wrote:So far all the storms have stayed north of south Louisiana, but there has been numerous supercells traversing central LA. I'm starting to think we won't really see any supercells this far south but the squall line forming west of Houston will be downright nasty by the time it gets here.

It already is ... (go to Squall Line Thread)

Scorpion wrote:F5?? I thought only the Plains states got those . Scary stuff. I would not be paid a million dollars to be within a mile of an F5.

Nope. LaPlata, MD was "downgraded" to a very high F-4.
F-5's have been recorded in OH and PA. Very rare but it happens.

Side note: The 1974 Xenia, OH F-5 was recorded on a a cassette approximately 1/2 mile away. If you wonder what these things sound like, this is amazing audio. The whistle near the end isn't a jet plane...it's the tornado passing right by. Turn up the speakers and close your eyes

http://www.midatlanticwx.com/sounds/xenia_tor.wav

Love chasing...would have been tense being that close.

Scott

OUCH

http://www.intellicast.com/Local/USLoca ... e&pid=none

Hey, Scott in VA-- I was thinking of starting a "1974 Super Tornado Outbreak Survivors" thread next spring, but I don't really get to call myself a survivor because my town wasn't hit-- we just had a large number of very close calls.

I love the Xenia tape-- I've had it on my desktop for years. Frightening, horrible thing!

chris