2014-04-26 FCST: KS OK TX

[LightiningRod]

I was thinking to combine a multi-day thread into one but I think this is fine. Let's get started.

This weekend I think is going to be the most interesting severe weather event so far this Spring season, particularly Sunday and perhaps Monday. A deep upper level low will be coming out of the West Coast by the end of this week. A surging LLJ across the Central and Southern Plains will allows dewpoints to reach in the mid 60s across the region. GFS depicts on Saturday that the dryline will be across the OK/TX Panhandles with strong surface based instability (SBCAPES around 4000 J/KG) and eroding CIN, the potential exists for VERY LARGE HAIL > 2 inches, damaging winds, and tornadoes (particularly close to the evening in West and Central OK when the 0-3 km helicities increases to around 300 m2/s2+). Some of the tornadoes maybe strong as result (EF2 or larger). Deep layer shear should be sufficient for robust updrafts and a discrete mode is favored as the bulk shear vector will remain perpendicular to the dryline. This will be the start of something potentially dangerous through the weekend and into Monday at least.

This setup this weekend should make storm chasers salivate particularly on Sunday and Monday when the deep upper level trough approaches the warm sector.

Best of luck storm chasers!

~Rod M.

 

[Logan Karsten]

Indeed, this weekend may be very interesting. I keep wating for the models to tone the event down, or do something to screw it up like they have been the past month. However, with each model run, Saturday is looking more and more dangerous for the western half of Oklahoma into southern Kansas. Upper level winds ramp up through the afternoon as the trough approaches from the west, and there will be an abundant amount of instability as the gulf is wide open for this event. Everything points to a classic severe weather outbreak for at least Saturday. Sunday to me is still up in the air as to where feature placement will be. It's still four days out, but unless things change significantly in the other direction, supercells with tornadoes are probable on Saturday afternoon/evening.

 

[Matt Hunt]

After watching this mid-week setup fall apart as the days went on, I'm not getting too excited for this one just yet, at least not until the NAM has a handle on it. The trend, however, is heading in the right direction, as opposed to the wrong direction for the mid-week setup. The 12z GFS would signal a monster day on Saturday for southern KS and western OK, even down into TX possibly. A well-defined dryline, mid-60s dews in the warm sector, 50 kts or so of 500 mb flow, and backed surface winds all look great. The 12z ECMWF is not quite as good, however, as a less well-defined dryline is progged, along with more meager moisture. Given the few days the southern plains will have to recover from this mid-week setup, and a much better trough that will not have ejected yet, I'm expecting better moisture than this first trough. Definitely one to watch, and I might even bite on a day before the day marginal setup on Friday as well.

 

[Chris Wilburn]

Hopefully, the GFS continues to paint what it has the last few days. The 00z GFS is near textbook for a classic tornado outbreak event from western OK into southern and central KS. Dewpoints mid to upper 60's and CAPE in excess of 4,000 J/kg is forecasted. Very deep 992mb surface low forecasted in eastern CO with a warm front arcing into northern KS up to along the KS/NE border with a dryline NW KS down to NW TX. I know this is way too early for specifics, but central KS just northwest of KS is absolutely amaznig with nicely backed surface winds along the dryline and just south of the warm front. Like I said, way too early for details, but if the 00z GFS verifies, it's going to be a very long day for towns in KS esp, and into OK. Forecasted hodograph for Wichita is very nice with VERY nice directional sheer. Also, good thing about Saturday is the 500mb winds are only forecasted to be in the 30-40kt range. The Wichita sounding has storm speed at 19kts, and I will take that for sure. Like I said too early, but hard no to get excited. Hopefully, this trend continues.

Like you mentioned above Matt, I will like to see how the NAM forecasts things first too before getting too excited. The NAM is on board for Saturday evening with the next 12z run, so we will see soon enough. I hope it falls in line at least close to the GFS, and we are in business. Also, like you mentioned, moisture will definitely not be an issue as we have a few days of moisture streaming in from the Gulf.

 

[Mike Johnston]

Chris, agree that this setup does look to have some hallmarks of a classic outbreak. Besides the factors you mention, notice that there are signs of a NEGATIVELY TILTED TROUGH. It's a little more pronounced on the GFS than the NAM, at least as of 12z Saturday. A negatively tilted trough can be like the straw that stirs the drink for severe weather setups, especially when coming atop a broad and juicy warm sector - supporting and enhancing the ingredients. Whether it will be the dry line itself or the warm front that provides the low level convergence / lift for initiation, it's hard to say yet. At the risk of sounding too dramatic, it looks somewhat like the setup on a certain other April 26th date in history.

EDIT: The new NAM run today is more pronounced in showing a negatively tilted trough. Looks like the evolution of the system on the NAM is just a little bit slower than the GFS, though.

 

[Adam Adkins]

The models are absolutely hopeless in regards to where this stacked low is going to end up on Saturday, and afterwards for that matter. With my experience of CO positioned lows I think that it is most likely that the sfc low will keep further west towards the front range rather than eastern Colorado, and this is echoed to some degree by the latest AFD. I think the possibility of severe will be extended northwest into northeast CO where there may be a triple point - I am liking the looks of this incredibly favorably sheared environment. Where will the surface low really end up?

 

[Andrew Stoller]

The only fly in the ointment for Saturday I can see is, if the models are indeed too fast with the trough, the upper level support will be a bit far west of the dryline/moist axis. The system going through the plains today is gonna sweep out the moisture. If we can get good quick return flow Friday and Saturday to where the dryline ends up further west towards the trough base, there will be high end severe Sat. with potential isolated discrete supercellular convection.

 

[Skip Talbot]

12z NAM looks like a nice slight risk with a few isolated cells down the dryline from NE to OK and a couple of tornadoes possible at dusk or after dark. Lack of large scale forcing as the trough lags to the west, and capping should limit storm coverage and delay initiation. Lack of low level instability and capping may also preclude tornadogenesis until dusk or after when the boundary layer cools, moisture advection continues especially on the northern end of the setup, and when the low level jet cranks up. Otherwise, we may have some initially high based supercells as storms form on the dryline where the T/Td spreads are higher than further east.

A cap bust is possible, given a 3C lid strength index sticking around through 21z, but it opens up at 0z and hopefully as the boundary layer cools, the trough continues to nose in, and that LLJ ramps up it should be show time by evening. The good news is that we'll probably have some discrete supercells and they'll be spread out across a few hundred miles of dryline so hopefully the weekend chase convergence is less of an issue.

Not sure on which end of the setup is most favorable. The northern end up in Nebraska may be more favorable in terms of capping and cells will be closer to the helicity by the warm front. However, this area is further removed from the upper level support. Cells further south into KS and OK may have better upper level support and as the diverging southwesterlies overtake the dryline by evening, and the cranking LLJ should make those veering wind profiles more than favorable for supercells and tornadoes even in the absence of the warm front. 700 mb temps start to get a little toasty as you go south though so that cap might bite.

 

[Zack Cooper]

The 12z NAM has a lot of potential, and a lot of problems. The pros: A lot of real good, quality moisture return, and a sharp dryline with backed surface winds all up and down it. A lot of instability, with CAPE values exceeding 2500 j/kg basically everywhere you look. A relatively strong LLJ and the shear is pretty impressive.

I have some big concerns if the 12z is to be trusted however. As Skip stated, the upper air support lags out west until 00z. With southern extent, capping is an issue. Also, I would like to see the winds backed a little more at 850. Also, LCL heights in KS may be a little higher, nearing 2000 m.

Regardless, it has potential to be a really nice day somewhere.

 

[Logan Karsten]

Guys, be careful reading into the 84 hour NAM forecast. It has proven to be not so reliable that far out. It may be underdoing the moisture, and backing of the surface winds (remember last year?). I suspect moisture will be higher than the NAM and a hair lower than what the GFS is currently progging. I think 3K+ of CAPE isn't an unreasonable expectation. I do agree with the timing of the upper level support being a potential issue here. I would like the system to either speed up a bit for Saturday, or slow down a bit for Sunday. Either way, I think Saturday has some real potential. As far as surface features go, I trust the GFS much more than NAM at this point, and it is continuously breaking storms out along the DL in western OK Saturday evening. I would say Saturday has huge potential if the forcing does not slow down anymore.

EDIT: Right after I typed this, I see the 12Z ECMWF, which has slowed things down considerably and is starting to make Sunday look extremely interesting.

 

[Matt Hunt]

Logan, I agree, and that's exactly what happened with the system for today. At 84 hours the NAM had less moisture than what it had by yesterday and today. It has also been a little low so far this season as I understand. The upper level support may not be great, but it does look like 40-50 kts at 500mb along the dryline right at, or just after 00z. The good thing about that will be slower moving storms. I'm still torn on where to target, but of course those details won't be worked out until later anyway. The better helicity looks to be along the warm front, but the NAM is also showing N storm motions, so I'm worried about storms firing and then crossing the boundary.

 

[Dan Robinson]

I was going to comment on the apparently circuitous route the moist axis was taking to get up north, until I realized I was looking at the 850mb plots, not the surface. The CAPE axis had the 'look' that it was more due to pooling rather than a deep, rich and wide warm sector.

 

[Zack Cooper]

The 06Z NAM looks pretty impressive near 00Z Sunday over W Central OK. Like the Elk City area. Upper air support arriving with the LLJ strengthening to 35-40 kt out of the South. 0-3km SRH 300-400 m2/s2 with large, looping hodographs. Substantial instability and moisture with backed sfc winds along the dryline. I do have a big concern however, and that is LCL heights of near 2000 m over this same area, and in fact much of the risk area on Saturday. Could be a big limit on the event, we will see.

 

[Shane Adams]

The 06Z NAM looks pretty impressive near 00Z Sunday over W Central OK. Like the Elk City area. Upper air support arriving with the LLJ strengthening to 35-40 kt out of the South. 0-3km SRH 300-400 m2/s2 with large, looping hodographs. Substantial instability and moisture with backed sfc winds along the dryline. I do have a big concern however, and that is LCL heights of near 2000 m over this same area, and in fact much of the risk area on Saturday. Could be a big limit on the event, we will see.

Not seeing the moisture you're talking about in SW OK. The deep moisture looks to remain well east of the upper support. As it stands right now, Saturday is starting to look like a repeat of yesterday. Depressing.

 

[Brandon Jenkins]

Not seeing the moisture you're talking about in SW OK. The deep moisture looks to remain well east of the upper support. As it stands right now, Saturday is starting to look like a repeat of yesterday. Depressing.

Agreed. After seeing how poorly moisture advected yesterday I certainly question current forecasts for the weekend. The GFS is significantly overdoing moisture as it progged mid 60's to northern ok yesterday which turned out to be mid 40's realized, I would expect a similar setup on Saturday with shallow moisture spread east of the dryline that mixes out substantially as the day drags on. High LCL's will narrow the window for tornadic activity to the 23-01z time frame as the BL cools and before it decouples as the cap roars back in after dark. Definitely still a decent ceiling on this event but tornadic potential has been tempered significantly on Saturday. Would not rule out a mesoscale accident or two given the strong thermodynamics and wind fields along the dryline, but not as optimistic as I was a couple days ago.