2015-04-08 EVENT: KS/OK/TX/MO/AR

[Lanny Dean]

EDIT - PLEASE NOTE that I had issues trying to post images/URL links.

Appears that a significant severe weather event is shaping up from mid week to late week as a multiday event possibly starting as early as Tuesday. Of real interest seems to be the Wednesday/Thursday timeframe as of right now. Latest model guidance (GFS and Euro) have been very consistent during the last 84 hours from run to run and indicates a more traditional spring setup - powerful mid and upper trough swinging out into the plains area

As it stand right now, it would appear that Wednesday *may* have the "better" dynamics (shear- direction and speed, introduction of the trough, 45kt southwest push at H7 with temps nearing 7-10 degrees C, 30kts+ southerly at H85, and 20-25kts at the basement) 850-500mb cross over simulation is not quiet as interesting. However, strong instability on both models look interesting: Simulated ML CAPE values up the I-35 corridor (Salina,KS to OKC) in excess of 3000j/kg with LI's -9 to -11. Lifted Condensation Levels through this area are more than doable with simulations of 750m or less as well.

The only caveat that might be realized for Wednesday is the quality of moisture return. GFS is currently painting 65* dews with a very sharp surface dryline extending from far northern KS to TX. Concerns for the depth and quality of moisture may play a role, as may the CAP if temps near H7 increase above current advertised. But experience tells me that this could be the "day before the day" with isolated supercells producing all modes severe. Appears that a DL retreat will aid in setting the stage for Thursday

Of more interest, at least on a broader scale, is Thursday. Model consensus in pushing the DL further east as the trough ejects and taking a true negative tilt. The tilt *may* lessen the tornado potential as depicted with current GFS solution but increase the overall severe potential. 18z and 0z showed classic forcing but admittedly the 0z run 850-500 looks like the low is stacking to some degree. This can be seen in the simulated hodos from ICT east towards Pittsburg, Kansas. Latest Skew-t was more impressive as well and if verified we *could* be looking at a significant severe/tornado outbreak.

 

[Russ Conlon]

What gets me excited about Wednesday is seeing GFS projecting low level shear at 40-60 kt between 850 MB to 700 MB for south central KS and central OK considering all the other favorable dynamics models are already pointing out. Long track tornadoes show up a lot in scenarios like this. Looking forward to seeing future NAM runs over the next 12 hours.

 

[Andy Berrington]

Doing some further analysis of the 00z Euro, looks very robust over Oklahoma starting at around 21z (initiation) Wednesday. The low level flow is already southerly to slightly backed at that time with 2500-3500 J/kg CAPE east of the dryline. The left exit region of the sub-tropical jet is also placed firmly over the area. By 00z, there is a 40-45+ kt southerly low level jet with rather strongly backed near-sfc winds feeding directly into the storms (instability/other parameters appear to be skewed at this point on the model output due to the ongoing storms) and 40-50 kts of 0-6 km shear oriented directly across the dryline. In my mind, there's little doubt that this scenario would yield the potential for tornadoes, perhaps strong. Unfortunately, this would also mean Oklahoma City is placed in the bullseye once again. Obviously, the danger for the the trough to be a bit off-timed/capping to snuff it out is still certainly there, along with the other usual caveats (although junk convection having any noticeable effect, at least carrying over from Tuesday, is likely mitigated by the lack of anything more than isolated storms). Moisture mixing out also seems less likely though due to multiple days of strong deep moisture return from the western Gulf and Caribbean.

The 00z GFS was also impressive, shifted a bit further north towards the KS/OK border region. This is all obviously looking at Wednesday in a bubble, will post more thoughts on Thursday later.

 

[Steve Miller]

STAFF NOTE: We have assigned this thread as "2015-04-08 EVENT: KS/OK/TX/MO/AR". Please start another thread for different event dates. This will be a very busy weather week and we'll want to keep things in order.
Thanks!

 

[Trey Thee]

This setup is looking potent, more like a late April setup.

My concerns at this point are timing of trough and deepening of the low. Capping will be in place but it seems forcing mechanisms will be in place. If I can't get out Wednesday then hopefully Thursday if not both days.

 

[Marcus Diaz]

12z NAM came in. My reaction:

Oh man I've never been happier to be alive. The NAM came in agreement with what the GFS has been saying all along. Very big numbers on the helicity side, cap eroded by 21z with amble forcing, screaming 40kt LLJ, and a large area of great chasing along the 183 corridor from I-70 down to NW TX. This is it, Mother Nature stopped hitting that snooze button. #2015awakens #wedgefest2015

 

[Trey Thee]

12z NAM came in. My reaction:

Oh man I've never been happier to be alive. The NAM came in agreement with what the GFS has been saying all along. Very big numbers on the helicity side, cap eroded by 21z with amble forcing, screaming 40kt LLJ, and a large area of great chasing along the 183 corridor from I-70 down to NW TX. This is it, Mother Nature stopped hitting that snooze button. #2015awakens #wedgefest2015

It certainly looks potent. Wednesday especially. I do think east of I35 could see two days of significant severe weather. It's certainly too early to call Thursday a go but at this it's looking a bit messy. The show in E OK would be earlier in the day it seems at this point. While possible and not unheard of it makes me wonder if the atmosphere will still be worked over from the convection on Wednesday.

 

[Caleb Grunzke]

Been loving Wednesday since Saturday morning. And now with the 12Z GFS speeding up the propagation of the system and the overall messier vertical wind field for Thursday, Wednesday looks to be the day. The metro areas of Wichita and OKC (what else is new...) are at risk and I really hope things do not turn ugly as some significant tornadoes look to be expected.

 

[Andy Berrington]

So we have 70s dewpoints on the Texas Coast three days before an event in early April. Buckle down...

 

[Trey Thee]

So we have 70s dewpoints on the Texas Coast three days before an event in early April. Buckle down...

Andy I agree completely. I've been perusing wind profiles for the next few days and this really has the feel of a May system with deep moisture advecting into the region. With the ingredients coming together, Wednesday certainly has the potential to be a high end event. I've already mentioned it to friends and family in OKC.

 

[Skip Talbot]

It's hard to find negatives with Wednesday as advertised on the 12z and 18z NAM.

Seeing this pattern, tight triple point gradient, and maxed out values on the sig tor plot melts my frozen heart. It's a beautiful surface pattern over great chase country with everything in place.



The obvious play to me is to catch a storm coming off the dryline south of the triple point, having it mature across the warm sector and then tornado as it approaches the warm front:



A couple reasons to avoid the obvious play: storm mode might be HP due to low LCL heights near the warm front. The other is chaser convergence, since SPC and the severe parameters will have a bullseye on this spot.

There's great news for those that don't like chaser convergence though.

21z Lid Strength (the thickness of the cap) supports initiation of surface based storms by late afternoon down the length of the warm front and well down the dryline. Storms will probably pop first on the warm front first if there's some sort of downstream impulse over eastern KS, MO, and IL. There'd easily be a tornado play there. The triple point will be the hotspot next, but storm coverage and mode might make you consider playing down the dryline. The cap is just starting to open at 21z down the dryline so you'll have to be patient:



That's ideal because you're storm is going to peak when the lighting and shear/instability combos are best. The capping should keep storms more discrete down the dryline too, and also spread chasers out down the length of the dryline from central KS well into Oklahoma.

Storm relative helicity goes bonkers once the low level jet ramps up by evening.


Sig tor is pushing off the charts between 7pm and 10pm. Another reason to try south in Oklahoma for that huge Tail-End-Charlie supercell.

What's going to screw this setup up? GFS is hinting at capping issues down the dryline. If the system slows any more causing that trough to lag, we may have some issues with lift and shear as those awesome looking 50 and 60 knot 500 mb winds are going to be hanging way out west.

 

[Andy Berrington]

Another negative could be the relatively weak upper level (above 500 mb) flow projected by the NAM, which may hint at HP tendencies. With that said, this would likely be a non-issue on the GFS/Euro solutions. Excellent diffluence aloft across all of the models though.

 

[Bob Schafer]

Not exactly what you were expecting? From today's 18Z NAM run, the 3-hour precip forecast ending 03Z, Wednesday night:



That stuff up around Concordia would be north of the WF. Head scratcher, huh?

 

[chrisbray]

Not exactly what you were expecting? From today's 18Z NAM run, the 3-hour precip forecast ending 03Z, Wednesday night:

View attachment 7454

That stuff up around Concordia would be north of the WF. Head scratcher, huh?

That NAM run's own simulated reflectivity shows storms firing along the dryline and WF, as well as the convective precip parameter so I am not sure what that would be.

 

[Kevin Rider]

I try and not get caught up in the hype of these type of setups until the system is actually on shore. With that said, Wednesday sure looks pretty good right now for tornadoes. Lots of instability, breakable cap, low LCLs, you name it. Seems too good to be true! I tend to question moisture and moisture depth on a lot of setups. I did check to see if the 18z NAM was initializing surface dewpoints and it did a pretty good job.