2013-05-18 FCST: TX/OK/KS/NE

[Brian McKibben]

This looks like it might be the best chase day of the year so far (of course this is still 6 days out). GFS has an impressive moisture field and LLJ of 50-60kts.

Here is a forecast sounding for 00z. The cap could prove to be quite stout, but the further north you get on the DL the better your chances for initiation.

For now, I will leave out a more detailed discussion and dream of the possibilities. It will be interesting to see how the WRF/NAM handle the 500 hPa trough.

 

[Chris Wilburn]

Moisture, instability, and wind shear are all very impressive on the 12z GFS. Strong 850mb winds of close to 50kts and higher in some locations. 500mb winds are strong too, but not to the point where storm speeds are 50+ mph either. Too early to get too detailed. It's nice to see something promising on the horizon. It wil be interesting to see what the NAM says in regards to the trough. The NAM will pick up on Saturday with its 12z Wednesday run. Hopefully this mornings run of the GFS verifies, if so, this should be the best chase day of the year. It's going to be a circus out there though. Hopefully the target area will be wide. Looks like an I-35 in KS to western OK event as things stand on the GFS. Kind of looks like 4/14/12 in regards to what areas will be affected.

 

[Jeff Duda]

I've been watching this potential setup since the weekend. While it looks better than anything that has come our way this year, I remain skeptical on a number of details.

The GFS continues to blow up grid-point storms between 18Z and 00Z, which precludes a legitimate analysis of the wind and thermal structure of the atmosphere at 00Z. At 18Z, mid-level flow is much weaker and low-level flow is quite veered as would be expected ahead of the good energy (shortwave itself). Areas that are not interfered do appear to tighten up in terms of the wind direction and speed, but I'm not that impressed on an absolute scale. I see 40-50 kts in places MAYBE. Also, if we end up getting 50 kts at 850 mb as the 12Z GFS progged, shear will decrease (because 500 mb flow will be about the same speed) and storm motion will significantly increase.

I've also become worried about capping. While the GFS typically overdoes moisture return, in comparing it to the NAM, through even 84 hours there is quite a bit of agreement between the two, so I'm not convinced such low-level moisture will not materialize. However, I see a lot of warm low-mid level temps above the PBL. For example, the forecast sounding Brian M. (OP) posted shows pathetic lapse rates between the surface and 700 mb. Perhaps through interference from precipitation processes, lapse rates are much better at 18Z, although that is partially because there is a big dry bulge across OK/KS showing up in various places as well. Perhaps that will help keep capping strong enough for instability to really build up, or it will result in early high based storms that could kill off the rest of an area for the day. It's a little early to be fretting about such details, but I certainly hope the tendency is for increased mid-level flow and cooling between 850 and 700 mb. Obviously, time will sort out the details for us.

 

[Bob Hartig]

Jeff, thanks for sharing your excellent analytical insights. I think this is an instance where my lack of technical knowledge on what things affect the performance of the GFS (and other models) hobbles my ability to read between the lines. Frankly, the GFS has been driving me nuts these past few runs with the 500 mb winds backing off, and capping wants to hose much of the show. If I buy the present scenario, I might find myself up in SD rather than northern KS/NE. And while I'm at it, off-topic for a second, I HATE what the GFS is doing on Sunday for everwhere except along the OK/TX dryline, and I hope the Euro kicks its butt. That's for a separate thread, but I just had to get it off my chest.

Anyway, one thing I've noted is that the 84-hour NAM for 18Z Friday is more aggressive with the H5 jet than the GFS and also wants to drop it somewhat farther south. That is a glimmer of hope for Saturday, and I hope it's on the money.

 

[Logan Karsten]

My excitement for this setup isn't as solid as it was 24 hours ago. The lack of solid 45+ 500 mb flow in the 12Z GFS is concerning me. It seems as though there is only a pocket across the Western Half of Kansas. In addition, it looks increasingly capped across the TX/OK panhandles. At the moment, the best conditions look to be across West-Central/Northwest Kansas where a subtle shortwave will ride the larger trough, providing upper-level support in that region. Hoping that future model runs bring better flow back into this system....

 

[Jacob Ferden]

My take on the 12z GFS is that the issue lies not just with how strong the flow is, but where it is. The 500s are backed by 0z Sat night to the point where all you likely would see would be a linear evolution in NW KS, if anything went at all. The cap it's suggesting farther south where directional shear is better would almost definitely be unbreakable, as the forcing would be to the west of the good moisture. Really hoping the ECMWF's idea of a slower ejection turns out to be correct, or this system may wind up being something of a non-event.

 

[John Gnuechtel]

I've been going off the GFS until other models start to show up in F5. Based on that, it still seems like the main play will be on the triple point somewhere in the neighborhood of I-70 in Central Kansas. That's what I'm looking at getting to at least; or somewhat north of there. The upper support looks kinda cruddy compared to a day or two ago; too slow for daylight perhaps. After 9 years of doing this, I'd still rank myself as a novice, so I'd like to hear what others think at this point.

 

[Warren Faidley]

Friday, Saturday and Sunday are still too far out to pinpoint a location, timing, severity, etc. Even tomorrow and Thursday are in flux. It's still "wishcasting" this far out. ATM, I pay more attention to the local NWS forecast discussions since they devote their entire attention towards a specific region and generally account for localized factors.

W.

 

[Derek Weston]

GFS latest continues the trend of weaker 500 flow/coverage in the plains on Saturday. NAM through 12z Sat also indicates that we won't get the robust mid/upper support we need. That said. . . next few days afterwards look to be pretty sweet, potentially. May still eek out a more localized threat Saturday. (and if the GFS is to be believe -- in Western KS... not bad chase territory)

 

[Jeff Duda]

After checking the latest trends in the models (especially now that the the day is in range of the NAM), I am pretty much writing off this day personally. The risk seems to have decreased and moved to the point where it wouldn't be worth my drive to the only remaining target area painted by the models - northwest KS/southwest NE/northeast CO. This appears to be the one area where rich moisture remains far enough west to be under the area of best forcing and flow. The dryline appears to surge well out ahead of the approaching mid-level flow in TX/OK rendering the area with no combination of shear and CAPE. Also, progged 700 mb temps have also increased across much of KS and the OK/TX PHs, thus making capping even more of a concern. There's still a possibility something could happen in SD, although 500 mb flow is even weaker north of the NE/SD border.

At this point, Sunday and Monday now look much more interesting, so I will turn my focus over to those days. Good luck to anyone who chooses to chase Saturday.

 

[Zack Hargrove]

I still think there is potential for SW KS personally on Saturday. The 12z GFS breaks out a storm in the area during the evening and the parameters are pretty nice. Here's the sounding and hodo for the area:

The cap is pretty stout but there are weakness here and there all around the area. And with the strong surface convergence, it may be breakable. The upper level wind profile isn't gorgeous, but with that much CAPE it may not matter.

 

[Marcus Diaz]

Backed-veered-backed winds, lot of CIN, Convective temp of 96, weak 0-3km CAPE. Like Jeff said, probably going wait till Sunday to head out. All these days leading up are capped until the trough begins to eject where we'll get those steep lapse rates and get the cap to erode.

 

[Zack Hargrove]

Oh I completely agree there are issues, but I think there is still a chance at an isolated beast or two if you're in the right place. Definitely not looking at any kind of outbreak Saturday.

 

[samuel stone]

I tend to side with zack on this one. especially since 0z runs of the nam and gfs both indicate better midlevel flow than was previously shown, for any storm which can develop. 0z nam shows quite a bit of convergence along the dryline between woodward and liberal and surface temps right along the dryline getting well into the 90s and a decent vortmax at 500mb at 21z, in accordance with what seems to me like a slightly sped up trough vs previous runs. also of note, yes, lcls will suck if a storm develops in that area but storm motions will be quite northerly streering it into much lower t/td depressions only about 50-75 miles north. also EhI's don't look too shabby in southern Kansas either. I know this is crazy, and by no means an exact match, but this seams a little similar to Greensburg, which was also a day-before-the day set up with a loaded gun scenario where initiation was quite questionable and had almost southerly mid lvl flow.. If there was a little stronger flow id call it a match. I'm sorry I just had to let that out haha EDIT: upon review, may 4 2007 did exhibit more swerly then sswly at 500mb at 0z. BUT. note that 500 mb flow was in the process of backing during that period and was probably was more so by 03z (near time of peak intensity)

 

[samuel stone]

well 0z run of the nam tonight continues to breakout healthy precip along the dryline AOA beaver and shift in NNE into sc/sw Kansas(generally based on an average of the last 3 or 4 runs). I lean toward believing this resolution since the surface will be well mixed and very hot along the dryline, convergence will be significant, and the models have not yet had a run come out where this was not shown. If this happens, and shear is sufficient(bit of a question mark I agree) then id expect one or two supercells with very large hail and the risk of a tornado to move through nw Oklahoma and southern Kansas between 7 and 10 pm. its a weekend.... if this continues to look this way ill be out for sure, not sure why one would not at least try in a year like this. unless prior engagements prevent it? Also I would definitely not ignore far nw Kansas and southwest Nebraska/ne colorado. its just further from me so I probably wont head that way unless my target falls apart.