2012-04-13 FCST: KS/OK/NE/IA/TX

[Skip Talbot]

Friday looks like a fairly potent severe weather setup across the plains. The trough, which is just nosing into the plains on Thursday is forecast to be well established over the plains warm sector on Friday. Moisture advection looks to continue throughout the period, with dewpoints into the low 60's extending across a much wider warm sector than the day before and as far north as central Iowa.

I see a couple of targets here just looking at this morning's run. The first is up in southeast Nebraska, where the NAM is showing a small surface low. Lift should be enhanced and winds better backed in that vicinity resulting in sort of a triple point play. With moderate instability over 2000 J/Kg and a 70 knot shortwave ejecting over this area by mid afternoon, shear and instability combinations should be very favorable for large supercells and maybe a few tornadoes.

http://www.twisterdata.com/data/mod..._221_2012041012_F81_DPTF_2_M_ABOVE_GROUND.png
http://www.twisterdata.com/data/mod.../10/12/NAM_221_2012041012_F81_WSPD_500_MB.png

The dryline extends in a northeast to southwest fashion down to north central Oklahoma where it goes more southerly. That would be my next target. The winds will be better backed along the dryline there, and the midlevel flow more perpendicular allowing storms to get off the dryline and more into the warm sector. Storms speeds might be a little more manageable and coverage allowing for more discrete activity as this area is a bit more removed from the stronger speed shear and forcing to the north.

Curiously the cap, is forecast to erode very early in the day across the southern portions of the warm sector. The morning NAM has a huge squall line blowing up by mid afternoon and the northern end of the target area firing later. If that's the case, I'd probably lean on the NE end of the setup where instability and directional shear will be in a bit of a better combination. Otherwise, I'd say an area from Wichita into northern OK has an awesome veering wind profile and surface pattern for discrete supercells coming off in the dryline. If early activity doesn't botch the setup later in the afternoon and evening, that might be the place to be. Either way, the cap looks to be wide open by afternoon and with the large amount of lift from the established trough, this should be much more of a widespread event than Thursday.

 

[Dan Robinson]

Skip summarized this well, so I wont re-hash the basics of the setup. The earlier runs of the GFS had me leaning toward the warm front/surface low in NE Kansas/SE Nebraska due to fears of veering surface through 850mb winds farther south. However, with both the NAM and GFS showing less of the northern low and a more 'classic' high Plains surface low configuration along the KS/CO border to help back the low levels in KS, it appears the dryline in central Kansas will fortunately be more favored. The only concern I have is with the veering at 850mb shown by both models, aside from a more southerly trajectory south of the KS/OK border shown by the NAM (which seem anomalous considering the dominant southwesterly 850s everywhere else). That said, it's not a big concern considering all of the other positives that this day has going for it.

 

[Ben Toms]

This day has me a little bit confused. Nearly everything is panning out for a widespread severe weather outbreak across the central plains, except for one thing: the NAM is throwing out a massive squall at 18z. Looking at the forecast sounding at this time across Central Kansas, there is still a stout cap at 850mb. I'm hoping this means the NAM is just getting thrown off by something, but I can't find anything that would verify my hopes. Does anybody else have any ideas on what might be causing this squall?

 

[Jeff Duda]

This day has me a little bit confused. Nearly everything is panning out for a widespread severe weather outbreak across the central plains, except for one thing: the NAM is throwing out a massive squall at 18z. Looking at the forecast sounding at this time across Central Kansas, there is still a stout cap at 850mb. I'm hoping this means the NAM is just getting thrown off by something, but I can't find anything that would verify my hopes. Does anybody else have any ideas on what might be causing this squall?

I've been seeing the same thing between both the GFS, NAM, and SREF now. I wonder if there's just so little cap that it's not taking much to get storms to fire. There doesn't appear to be a strong disturbance embedded within the trough that would cause such widespread development. That precip across KS/OK/TX is really hurting instability. It would be a day killer. Good thing the NAM is a model and models have error, especially in their convective parameterizations. I'm hoping the model is overdoing the forcing or whatever disturbance is causing that crapvection to form. My gut says it is because I've seen precip patterns like that in the models so far this spring across OK that didn't verify.

 

[Seth Edge]

Yeah you cant put to much confidence in composite reflectivity(even in the RUC).As you prob already know. Its always off by at least a little. Its still good to look at to see where the model thinks the storms will initiate at first though and if they are in the daytime . But stated in the previous comment its prob. because of a little cap.

-Follow us on twitter(@EyesOnStorms)

 

[Andy Wade]

The NAM's been consistent with zero capping and early initiation for a while now. As far as what could kick off that convection, could old boundaries from Thursday night's storms out west be a factor? If it does go around 18z, I believe the squall line solution: 30 kt sfc-500 mb shear, CAPE ~ 2000, nonexistent cap.

Also worth noting, the 12z NAM breaks out more precip in far SW OK by 00z. Most parameters, except LCLs and possibly helicity, look as good down there as anywhere. If a squall line wipes out the rest of the state early in the day, that might be a respectable backup plan.

 

[Mike Smith]

I think many are underestimating Friday's potential. Per the 18Z NAM, there is a classic L-shaped hodograph at ICT ( www.twisterdata.com/index.php?sound...nding=y&output=image&view=large&archive=false )
with ≥2,000 j of mixed CAPE within 40 mi. and advecting north.

There is a boundary forecast from about P28 to EMP at 21Z.

All it would take is a jetmax or a small-scale shortwave to create significant tornadoes.

 

[Derek Weston]

Latest NAM run is disappointing. Upper level energy and 850s are displaced a bit. 500 jet streak runs through KS but is met with quite weak low level sheer. 0-1KM helicity is marginal... Will be interesting to see if this trend continues. Had been looking better. . . not a big fan of mediocre looking hodographs in the low levels. (at least Saturday looked amazing last run, be interesting to see tonight's run)

 

[samuel stone]

this has got to be one of the hardest days to forecast so far this spring. convective trends have so much to do with it and that is the area of meteorology we are least able to predict. as of now if we get sufficient recovery and not a large effect of warm moist air blocking from early convection then we may well have a solid tornado event on our hands in kansas. but anything less and i fear we may get nothing at all. atleast we still have saturday!

may 11th of last year may be the worst case example of what could happen

 

[jshields]

I'm not sure what to make of this day, at least tornado potential wise. Most model runs have had either veering low level winds or fairly weak low level flow or both resulting in rather poor low level shear. this has been seemingly getting better the last several runs, especially on the latest run of the NAM(12Z). instability is great across central and eastern KS on south and there is no cap whatsoever which would normally worry me that there would be too much junk. however, the NAM refuses to break out any precip as there appears to be a lack of a real strong trigger. Topeka WFO makes mention of a couple of weak boundaries in their area(weak warmfront and retreating dryline) and that will be what has to set off convection as the main trough is still pretty far west. I'm thinking any stuff that fires earlier will be mainly a hail and wind threat, but after 0Z when the low level jet kicks in, then I really think the tornado potential will increase. I'm also a bit worried that there could be tornadoes well past dark as the CIN doesn't really start to fill in til after midnight in central Kansas. right now I'm really liking south central Kansas the best as there appears to be a bit of dryline bulge and surface winds also really back to southeast after 6pm. Still on the fence about going out this day as it might be best to wait til the main show on Saturday

 

[Timothy Finn]

Just a curiousity question here.....

What are the possibilities that today's storms will leave behind an outflow boundary that can help trigger thunderstorms tomorrow in the S KS to N Central OK area? I'm just thinking this, because I see the wave ahead of the main trough, the dryline, and possibly this.

Just a thought.

Tim

 

[Mike Smith]

Just a curiousity question here.....

What are the possibilities that today's storms will leave behind an outflow boundary that can help trigger thunderstorms tomorrow in the S KS to N Central OK area? I'm just thinking this, because I see the wave ahead of the main trough, the dryline, and possibly this.

I think you have nailed it. I'm surprised no one is talking about tomorrow as it is a typical "day-before-the-day." The European model has a solid short wave trough at 00Z from just NE of ALS to ABQ moving rapidly northeast.

The models have been showing a boundary more or less along a EMP-WWD line or a little south.

The HRW-NMM shows weak convection along and just south of that boundary at 00Z. There is enough difluence over Kansas that -- if the short wave shown on the European is real -- that I would expect storms to rapidly develop into supercells, especially in KS, in the 23Z to 03Z period. That may be too late to chase, but I even believe tornadoes are possible.

Those will move northeast (as depicted on the NMM) during the night and will provide the "morning rain" so common to major tornado outbreaks on Saturday.

 

[James Aydelott]

I think you have nailed it. I'm surprised no one is talking about tomorrow as it is a typical "day-before-the-day."

Mike,

we've been mulling that over all afternoon in the office.

A retreating dryline will likely be the trigger in OK, but not to worry about that, Hugoton in 1996, and Lubbock in 1970 were both major tornadoes fired up on retreating drylines.

RPM 4km and 12km 21z runs both show supercells firing in central OK and moving off the retreating dryline to the NE.

on edit: now the 00z NAM and both 00z RPM runs are consistant with 21z RPM run

 

[Chris_Spannagle]

Are you referring to this site?
http://www.wxcaster.com/conus_0012_us_models.htm

If you scroll down you'll find: Lid Strength Index (LSI)
this gives you images that would look like this: http://wxcaster4.com/nam/CONUS_ETA212_ATMOS_LSI_24HR.gif

 

[Jesse Risley]

It still looks like today could be an interesting play in WC and NW OK and points close to that. Reviewing 12z Upper air data along with RUC and HRRR 500 mb vorticity and 700 mb VV plots for late this afternoon, it does appear that some embedded 45-50 kt speed cores will rotate out of TX/NM late this afternoon as the dryline orients itself in a more SW/NE orientation from near the KS border SW towards the TX panhandle region. Forecast Skew-T, Log-P profiles show ample CAPE and shear profiles for the maintenance of supercells, with steep lapse rates and LI values AOB -7C. 0-1 km shear profiles really improve late this evening as the H85 flow rebounds, so I would not be surprised to see tornado reports today, along with some rather significant hail and potentially some damaging wind gusts. The recent short-term convective models seem to be initiating convection proximal to the retreating pacific front late this afternoon (between 20z - 21z), most favorably W and NW of the greater OKC metro area.