2012-04-14 FCST: TX, OK, KS, NE, IA

[samuel stone]

While most of the focus is stil set on thursday and friday, saturday is shaping up nicely as well, Ill leave sunday on deck for now. Lee cyclogenesis ramps up again in the high plains late friday in response to the main jetsreak finally rounding the base of the trough. The moist sector will retrograde slightly overnight friday, and meet a surface dry punch coming out of new mexico by saturday afternoon. 0z GFS progs the dryline from far sc nebraska to central kansas and into western oklahoma to near wichita falls, tx by 0z sat. good chase country thats for sure. good nice quality moisture should be in place by this time as trajectories continue to slowly improve as we move towards the weekend and that pesky high over the southeast begins to push further east. as of right now it appears wind fields should be pretty favorable for sups and tors with any convection that develops on the dryline, im not even going to touch convective trends through the day im having enough headaches trying to do that for fridays setup already but i will say that 0z GFS progs very minimal cap once again with a huge gaping hole in inhibition by 18z and seasonably cool 700mb temps.

its quite early and i dont really like forcasting too much until the nam picks up anyway but thats right around the corner so i went ahead and pulled the trigger on it. In conclusion moisture should be of good quality and winds fields are looking favorable thats about all i look at this far out. no sense in looking at too many details right now. thoughts?

Edit: Mods go ahead and change the commas to back slashes in the title if need be. my mistake there

 

[Jeff Duda]

I've been suspecting for the past few days that Saturday was going to be one of the bigger days of this possible severe weather (dare I slip out the term "outbreak"?) sequence. One thing I hadn't liked much about it from a chasing standpoint was the veered low level winds. Today's 12Z NAM and GFS have the low level flow veered much less than in previous GFS forecasts. In fact, the NAM has more or less 180-190 winds at 850 mb at 00Z, while the GFS is still hanging on to SSWly winds. With great moisture (Tds exceeding 65 F across most of OK and extending into S KS) in a well-mixed PBL with LCL heights generally below 1000 m, suggestive of high PBL RH, combined with excellent backed low level winds and veering up to 60-70 kt SWly 500 mb winds, if this verifies it could be a substantial severe weather outbreak. Storm motion may be a tad on the faster side given the strong surface winds exceeding 20 kts yanking up that density weighted mean wind, but a storm that deviates from the mean motion vector in an environment with a hodograph as curved as they are would have a lot of storm relative flow to feed on.

It's still 3 days out, but I'm suddenly excited about this day since I know I can chase it.

 

[Matthew Piechota]

The 12z NAM was pretty much a textbook run for a outbreak type scenario for both KS and OK. Could also add southeast NE to that group with really nice looking hodographs up there.

 

[samuel stone]

similar thoughts as above on the 12z nam run. like jeff said the surface to 850mb winds have improved drastically from the 0z gfs. thats why i normally wait for the nam to pick up an event. but something told me this could be a big one and the 12z nam came through. if the nam shows this prognostification for another 2 or 3 runs. ill be head over heals about it. as of now im tryng to contain my excitement.(not working) i am entirely available to chase saturday and plan to do so. as of now i like the ks neb border for the best hodos and i also like the ks oklahoma border for best combinations shear/instability. for what its worth 12z nam only breaks out precip down to the ks ok border by 0z. if that verifies id love to be on the southern most cell as it sucks in unimpeded inflow.

 

[Russ Conlon]

I see pretty good agreement with the NAM and GFS on this day with the latest runs and it looks like it could be huge this day. A chaser could pick a spot from Iowa down to North Texas pretty much. Cap looks to start weakening at 1 p.m. in W OK and KS and no cap at 4 p.m. anywhere for pretty much most of Tornado Alley with latest 00Z NAM run. If that verifies, Katy bar the door.

 

[Aaron Shaffer]

I'd like to hear people's thoughts on chasing NW Iowa. With the triple point setting up there and a decent amount of light low-level directional shear - starting to peak my interest... although in full disclosure I am biased toward a more localized storm chase. Soundings are starting to look a bit more interesting, however, as the CIN gets eroded near the triple point by 21Z-00Z, mid-level shear stays decent, and CAPE increases. Anyone else targeting that area or am I wishcasting?

 

[jshields]

i think the triple point is usually always a great place to chase to start off with. storms will usually fire first along the triple point and then down the dryline/warmfront. i'd watch carefully though where the triple point will end up. most models/forecast discussions have the triple point back in central nebraska tomorrow late afternoon. you could play the warm front wherever that ends up in iowa, but i would be careful how far north and east you end up, so you're not where the convection is going to be elevated by the time it gets to where you are at.

I'd like to hear people's thoughts on chasing NW Iowa. With the triple point setting up there and a decent amount of light low-level directional shear - starting to peak my interest... although in full disclosure I am biased toward a more localized storm chase. Soundings are starting to look a bit more interesting, however, as the CIN gets eroded near the triple point by 21Z-00Z, mid-level shear stays decent, and CAPE increases. Anyone else targeting that area or am I wishcasting?

 

[Zack Cooper]

I see two potental targets for Saturday... One in NW MO into Iowa... and the much more obvious one central Oklahoma. Looks like a classic tornado outbreak scenario... I would like to see sfc winds a little more backed, but with such a potent trough... dewpoints in the 60's, and CAPE values of 2000 j/kg and above... I definitely think it will be a big day... Hodographs are pretty impressive too, especially over central OK... One concern I have, is models not initiating convection until 00Z or so, which could make it not a great chase day, but honestly... I think convective initiation will occur sooner. I'm not sure if I'll be chasing, but if I do... central Oklahoma looks like where I'll be... looks very nice.

 

[Greg Blumberg]

Just took a look at the 12 UTC NAM and GFS. There's some nice consistency between the two of them with the placement of the primary trough. In addition, as the 500 mb jet builds in, I see deepening in the NAM 12 UTC surface low which is in SW Kansas and SE Colorado. The low center gets to ~992 mb in both the GFS and the NAM. I took a closer look at the 12 UTC NAM, and to be honest, I'm a little bit worried about central Oklahoma. It's not very often that I see 850 winds go southerly with 40-50 knots at 18-21 UTC. Also, it's pegging 2000 - 3000 J/kg just east of I-35 in Oklahoma.

I just heard some concerns about storm speed. Per the 9 UTC SREF there is still some uncertainty in the 500 mb height gradient that will be over the Oklahoma target area, so I wouldn't quite say that storms will be flying just yet. Also, the evolution of Saturday will be heavily dependent upon how the convection today and tomorrow plays out, so variability in how each model handles convection each day will make things difficult to pin down.

 

[Trey Thee]

Looking at the 18Z GFS data vs the 18Z NAM data and there are some differences that haven't yet been ironed out. The GFS has significantly less instability in the forecast vs the NAM and the placement of the various features are different. The two models are both showing adequate shear and instability, I was expecting them to start coming into agreement more at this point. The GFS is about 75 further west with many of the features, the NAM is showing in excess of 3000j/kg over a broad area the GFS has a narrow area of 2200 to 2500 j/kg.
The models are still in pretty good agreement with the placement of the low and its strength. I believe the above issues will work themselves out. Upper air conditions and instability seem more than sufficient for a broad severe weather event for OK and KS on Saturday.
We'll head West on Saturday and move somewhere between OKC and Enid and see what happens.

 

[Derek Weston]

Looking at the 18Z GFS data vs the 18Z NAM data and there are some differences that haven't yet been ironed out. The GFS has significantly less instability in the forecast vs the NAM and the placement of the various features are different. The two models are both showing adequate shear and instability, I was expecting them to start coming into agreement more at this point. The GFS is about 75 further west with many of the features, the NAM is showing in excess of 3000j/kg over a broad area the GFS has a narrow area of 2200 to 2500 j/kg.
The models are still in pretty good agreement with the placement of the low and its strength. I believe the above issues will work themselves out. Upper air conditions and instability seem more than sufficient for a broad severe weather event for OK and KS on Saturday.
We'll head West on Saturday and move somewhere between OKC and Enid and see what happens.

NAM has been more optimistic about CAPE than the GFS all spring. (seemed it was this way the past few years, for that matter) I generally ditch the GFS when the NAM becomes available.

Looks like a potentially significant severe episode over a large region of the plains. My big interest -- being from the northern end of this -- is seeing how strong the northern end of the target looks. I expect the WF and triple point region to be active as well. If the latest NAM is any indication I expect the SPC to include E NEB and W IA in some of the stronger probs.

 

[Trey Thee]

NAM has been more optimistic about CAPE than the GFS all spring. (seemed it was this way the past few years, for that matter) I generally ditch the GFS when the NAM becomes available.

Looks like a potentially significant severe episode over a large region of the plains. My big interest -- being from the northern end of this -- is seeing how strong the northern end of the target looks. I expect the WF and triple point region to be active as well. If the latest NAM is any indication I expect the SPC to include E NEB and W IA in some of the stronger probs.

I agree, I generally tend to follow the NAM when it becomes available. Derek, I agree with your analysis of including E NE and W IA if the models hold till tomorrow morning I expect to see just that. I also think the MDT could move as for north as Omaha. At this point I see nothing to indicate an upgrade to high risk but I believe as the models move closer together and some of these details get worked out we could see that with the first DAY1 for Saturday (I'm making a few assumptions on this obviously).

This system is going to be potent regardless of the severe weather mode and it will impact several million people in densely populated areas. OKC approximately 1.3 million, Tulsa 900k, Wichita 725k, and if Omaha and the Western suburbs of KC get roped into the MDT then we'll have a huge coverage area impacting nearly ten million people. Not a good situation...

 

[Tim Supinie]

Latest NAM sounding for 03Z 15 April from ICT: http://bit.ly/I7MBwk

That's starting to look downright scary. I think it's mostly self-explanatory, but a very large hodograph + steep low-level lapse rates = bad, bad news. Add to that the 50-knot storm motions and the fact that it's well after dark and this is a bad forecast for the Wichita metro area.

EDIT: Well, if you're not already aware, we now have a Day 2 high risk with the strongest wording I think I've ever seen, much less in a Day 2 outlook.

 

[Ryan McGinnis]

I don't want to do the "only commenting on the SPC" thing, but when was the last time anyone remembers seeing a 60% hatched risk on day two?

Storm motions are progged at 40 to 45 knots to the northeast according to NAM / Bunkers; hope you all have your NASCAR licenses kept up to date.

 

[Derek Weston]

The SPC outlook seems warranted. Really not seeing anything to suggest this is anything but a major outbreak waiting to happen. Only hindrance would be limiting of instability... (not seeing how this happens currently) I guess if I had to get picky I'd say that I'd like more of an easterly component to the surface winds. Could turn just a bit more.

Comparing to the last two big high risk days in the region -- May 11,2010... May 24, 2011 -- we're see a slightly more sheared, slightly less juiced atmosphere... what you might expect for a mid April outbreak. Still looks huge.

The most remarkable aspect of this setup to me -- and what the SPC cited specifically in going High Risk -- is the area it covers. From Wichita Falls all the way northeast through Omaha -- running right the heart of the plains interstate system, I35 -- you've got a legit shot at strong tornadoes. Add to that a lifting warmfront that I'd expect to cause a bit of action through Northern Missouri into IA and you've got an enormous geographical area under the gun. This has the potential to be one of the largest outbreaks we've had over the past decade in the plains from a numbers point of view, I'm thinking.

As for the models not wanting to break out much in the way precip... not buying it. I remember this being the case as well May 11, 2010. Way too much forcing present. The 80-90kt 500 streak poking into KS won't let that happen. I'd be more worried with quality of coverage -- from a chasers perspective -- with the sort of shear we're dealing with. That said... should coverage hold off most of the day... we'll certainly be dealing with some behemoth supercells after dark. (and I'm kind of hoping we get on with this early so we don't have to deal with too many monsters lurking in the dark)

Pattern recognition tells me though that we'll have PDS watches shortly after if not by noon and initiation within a few hours of their issuance.

Another thought on a setup like this -- where do you chase? You can almost afford to be a bit picky with such a large area that ought to produce. Personally I'd like to stay away from the masses... I'm also not so fond of chasing east of I-35. The road network through the flint hills is rather sparse and uninviting from what I remember. West of I-35 in KS is just dandy, however. North Central Oklahoma is solid but will be packed to the brim with chasers. Enid area will be crawling, I bet. I'd be halfway tempted to see what I could get in southern Nebraska/Northern KS. (absolutely love the grid of Eastern Neb) Of course... I've not yet been let down by a high risk in Oklahoma... decisions, decisions.