2011-04-26 Now: TX,OK,AR,LA,MS,TN

[Jeff Piotrowski]

Tornado watch NC/NE TX SW AR extreme NW LA.

WF start to pop from TXK/SW.

 

[Justin Bailey]

looks like TCU develpoing along the dryline south of DFW on visible satelite.

 

[Michael Riedl]

Some of The Highest Probs I have seen.

The main Upper Level Dynamics are still about 30-45 minutes away, but once they arrive, it will be a dangerious situation. Winds are backing over the entire warm sector now.

SR Helicity will only increase as time goes on, especially if the 850 winds start to back more south.

TCU getting going on the Intersection of old OFB and dryline.

 

[Stuart Robinson]

Cap had just broken - South of DFW (near to Meridian)

 

[Jeff Duda]

I wouldn't use this word often, but it looks like an INCREDIBLE severe weather situation will unfold this afternoon into this evening. Forecast values of some indices are going to the top of the charts. I've seen RUC and NAM forecast values of STP up to 10, 0-1 km EHI values above 10, ESRH values > 500 m2/s2, and 0-6 km shear > 70 kts (with supercell storm speed only up to about 40 kts). Several consecutive runs of the HRRR this morning are calling for two waves of convection to develop: one along the warm front in N LA/S AR/far NE TX during the early-late afternoon hours, the other along the dryline initiating around 00Z. The model looks to have a storm mode of clusters of embedded supercells over the eastern area and more isolated supercells over the western area. However, as mentioned above, towering CU are already going up along the dryline, so this may end up being a long event in both areas.

SBCAPE is already over 3000 J/kg over much of the southern US and maxes out around 5000 just south and east of the Dallas metro area. This CAPE has less than 25 J/kg of CIN to work though, so initiation cannot be far off now (LFC heights are also very low in the eastern half of TX south of the warm front). There is also a large area of > 100 J/kg of 0-3 km CAPE, and maxes up to 200 near where the SBCAPE max is. Effective deep layer shear values are over 50 kts over a very large area (most of the southern-central US) and maxes up to 70 kts are seen over the dryline in C TX. This is progged to increase as the shortwave fully moves in. 0-1 km shear is currently around 15-25 kts in E TX, but less elsewhere. This will increase big time as the LLJ builds in late this afternoon and into the early evening. These features are driving up the composite indices. I see STP maxing out around 6 in E TX right now, and the EHIs are also high (up to 6-8 across much of E TX). VGP is pretty high just south of Dallas (>0.4) and Bulk Richardson numbers are generally > 50, but between 50-60 in a large strip near the warm front, thus suggesting supercells are likely to be mixed with some multicells.

Quite a scenario setting up.

 

[Rowland Beardsell]

First post so here goes!

In short, meteorologically speaking there is a very nice combination of a strong jet streak and exit region plus the rapid development of a sfc low, steepening lapse rates rapidly and increasing the LLJ rapidly throughout the warm sector region. Did I say rapid enough times? There will be a serious amount of vigourous atmospheric instabilty today across the high risk area, especially for mine in TX where CAPE/shear balance will be the best plus the more discrete modes likely from cap break which will be pretty impressive. I'd be trying hard to settle around remnant OFB's for initiation but keeping in mind the position of the jet streak for downstream cap breaking as well. The return flow will be something to behold I think once the setup gets cranking and a critical point will be where the nose of the sharpening mid-level jet intersects the dryline/warm front boundary and the associated timing of that intersection for a heads up to when storms will start to get serious. The inflow will probably be one of those inflow days that causes damage let alone anything else. Definitely expect powerful inflow and large helicity. So in short, multiple severe supercell thunderstorms outbreaking across TX/SE OK/AR, especially 'textbook' for mine in TX but the AR potential is also super high for high-end tornadic supercells tracking WELL into the night. Dangerous chase territory that will be so take care there. Eventually things will become linear and a very large and strong MCS will form, with serious straight line wind potential. Also, (especially in TX) watch out for very large hail given the shear/CAPE combo, what we saw yesterday will be repeated in the size department today.

 

[Trey Thee]

I wouldn't use this word often, but it looks like an INCREDIBLE severe weather situation will unfold this afternoon into this evening. Forecast values of some indices are going to the top of the charts. I've seen RUC and NAM forecast values of STP up to 10, 0-1 km EHI values above 10, ESRH values > 500 m2/s2, and 0-6 km shear > 70 kts (with supercell storm speed only up to about 40 kts). Several consecutive runs of the HRRR this morning are calling for two waves of convection to develop: one along the warm front in N LA/S AR/far NE TX during the early-late afternoon hours, the other along the dryline initiating around 00Z. The model looks to have a storm mode of clusters of embedded supercells over the eastern area and more isolated supercells over the western area. However, as mentioned above, towering CU are already going up along the dryline, so this may end up being a long event in both areas.

SBCAPE is already over 3000 J/kg over much of the southern US and maxes out around 5000 just south and east of the Dallas metro area. This CAPE has less than 25 J/kg of CIN to work though, so initiation cannot be far off now (LFC heights are also very low in the eastern half of TX south of the warm front). There is also a large area of > 100 J/kg of 0-3 km CAPE, and maxes up to 200 near where the SBCAPE max is. Effective deep layer shear values are over 50 kts over a very large area (most of the southern-central US) and maxes up to 70 kts are seen over the dryline in C TX. This is progged to increase as the shortwave fully moves in. 0-1 km shear is currently around 15-25 kts in E TX, but less elsewhere. This will increase big time as the LLJ builds in late this afternoon and into the early evening. These features are driving up the composite indices. I see STP maxing out around 6 in E TX right now, and the EHIs are also high (up to 6-8 across much of E TX). VGP is pretty high just south of Dallas (>0.4) and Bulk Richardson numbers are generally > 50, but between 50-60 in a large strip near the warm front, thus suggesting supercells are likely to be mixed with some multicells.

Quite a scenario setting up.

This is definitley an impressive setup. To be honest its a bit scary given the breadth of the high risk area and dynamics in place to support it. As mentioned in the FCAST thread, the DFW metroplex could be under the gun as well. It is definitely starting to appear that way given the model trends and incredibly robust environment that is setting up. There are some good size metro areas that could be under the gun, Little Rock, Memphis and of course DFW. Well over ten million people within the confines of the risk area. I hope everyone is paying attention this afternoon and evening.

You mentioned VGP? What is that an acronym for?

At this point I think we'll see a substantial outbreak begin by about 4:30pm with convection taking off over the next hour. I am particularly worried about what may be the second round of storms in the DFW area. In many cases people expect these severe weather situations to be over with after the first round, especially those on the western edge. This does not appear to be the case tonight. In fact DFW may get skirted by the first round and hit pretty hard later this evening. Temps are rising rapidly across most of the area with another two or so hours of good heating left to go.

 

[Karen Politte]

The DFW cell is incredibly meaty-looking and probably has significant staying-power. It's split a little in the last few scans........

There's also some interesting stuff blowing up and rocketing north/northeast in AR. In trying to categorize this, I finished at the conclusion that it is WAA grunge being thrown up over the warm front and/or the outflow boundary that was visible on LZK's radar this morning, sagging southwards. Given it's speed and unexpected motion/heading, that's my best guess, at least. Nothing to say of course that this stuff couldn't become rooted sometime - but I still feel that our main show will originate in TX.

KP

 

[Adam Atkins]

Beautiful bell shaped wall cloud on Mikey Gribble's stream near Italy, TX.

http://weather.wdtinc.com/popout/index.php?M=10164&C=20226&O=10103

 

[Andrew Francis]

That cell east of Fort Smith AR came out of nowhere! Flying ENE towards I40. Looks pretty isolated compared to everything else going on with this event thus far. Wonder if anyone will be on this when it gets to the Interstate?

 

[MClarkson]

Seeing some half-decent velocity couplets southeast of the Dallas area. Also some hooks.

EDIT:

there is a solid hook and fairly tight rotation apparent on radar moving west from I35 towards I45, about 40 miles due south of Dallas.

 

[Dave Gore]

Incredible couplet on the cell moving into Memphis.

 

[J.B. Dixon]

The north side of Memphis looks got take a direct hit from an amazingly broad, intense circulation couplet on radar in minutes. This could get very serious.

Tornadic sup's as far as the eye can see. Incredible.

 

[E Hale]

What are the Odds? An incredibly impressive radar signature with likely tornado is occurring about 4 miles to the Northwest of where the Vilonia tornado tracked yesterday. When it rains, it pours.

 

[J Allen]

Very nasty conglomeration of tornadic supercells in eastern AR all the way up to Memphis, and a pretty evil looking couplet North of Little Rock (perhaps around Conway?) and things just seem to be backed up all the way to Dallas. And from the looks of it the situation is getting worse.