2011-05-11 FCST: KS/OK/TX

[Brian McKibben]

The 12z GFS shows much stronger 500 flow than previously anticipated. I know this is 180 hrs out, but it looks to be the first good chance of tornadoes across the plains.

http://climate.cod.edu/data/forecast/GFS/12/SP/gfsSP_500_spd_180.gif

Tds should be in the upper 60s / low 70s and the speed shear looks to be quite impressive.

A lot can change, but this looks to be the one to watch.

Forecast sounding looks pretty good if we can overcome the cap.

http://weather.admin.niu.edu/chaser/tempgif/26500.GIF

Your thoughts...

 

[Michael Riedl]

Way to far out to get too get to antsy, however I'd be lying if I said this date didn't caught my eye on the 12z GFS.

Some things I don't like....Pretty Highly amplified trough......but it takes forever to traverse the Western CONUS. Considering its progged to be in my area for once (gas prices are a killer) I will chase obviously, but I don't know how super excited I am going to be for 40 KNTS SSW at 500 MB. Maybe I am too picky.

That sounding is pretty Nice i Must say with 55 KNTS at 500.

 

[Mikey Gribble]

I've been watching this really closely for a couple days now. The ECMWF has been pretty damn consistent with the general theme. I think it was the Sunday 12Z run when I first looked at the ECMWF, and even though it only went out to next Sunday on that run, it was showing a deep trough over the west coast with a slight positive tilt and a strong jet moving into the back side of it. That's when it first caught my attention. At that time the GFS was showing a low amplitude wave zipping through the north central plains. Since that time the GFS has slowly started to move more in line with the ECMWF, showing a deeper and slower solution.
It still tough to pin down which day will hold the best potential for the plains. The GFS currently shows Wednesday being the big plains day, but the ECMWF is a little slower than the GFS. You also have to consider that the ECMWF has been much more consistent with this system and typically I think it is more accurate with timing this far out too. So I'm favoring the ECMWF on this one. Both models have shown a recent slowing trend (GFS to a greater degree). On top of that both models (especially GFS) tend to be too fast until you get inside 5 days or so. That is making me wonder if the trend of slowing this sytem down is done or will that trend continue. Assuming the ECMWF is the more accurate solution timing-wise at this point, it won't take much of a slow down to push the big day in the plains back to Thursday. Anyway, tough to pin down the best chase day in the plains at this point is what I'm getting at.

Regardless of what day this happens on, the models are both showing a high amplitude trough taking on a negative tilt as it ejects into the plains. Good moisture should already be in place, with dewpoints in the upper 60's and low 70's across the warm sector. Between that and the fact that it is now May, I am very optimistic about this setup.
The thing that really is getting my attention with this system is the very strong low level wind fields being forecast by both models. Anytime you see strong backing low level winds this time of year it is a red flag for tornado potential. Obviously small scale details play a big role in tornado potential and we are still a week out, so I'm in no way saying this will be a tornado outbreak, but you don't get many high amplitude troughs with a favorable tilt coming through the plains this time of year and not get a fair number of tornadoes (especially the case when moisture isn't an issue, which it doesn't appear to be).
Again a lot can change between now and then, but at this point it is starting to look like a synoptically evident severe/tornado event.

 

[Mikey Gribble]

The one real point of concern I'm having at this point is the GFS's trend of weakening the trough as it ejects into the plains. It's shown that on a few runs now, including the 00Z tonight. I haven't seen tonight's ECMWF yet though and I'm not going to worry about the GFS solution until the ECMWF starts to follow suit. It has been the much more consistent of the two models and it has been showing a stronger trough. As far out as we still are theres not much reason to get hung up on run to run details either. I'm sure it will all get shuffled around a bit between now and then.
The GFS does still show the bulk of the trough entering the plains on Wednesday, so its still looking like the most likely candidate for the best severe potential in the plains, but again too far out to put much stock in that.

 

[Brian McKibben]

New 12z GFS out. The wind field of this system looks more impressive than before. The moisture will be there with Tds in the 60s and 70s. Instability should not be a problem. I am concerned with the stronger cap to the south and the possibility that the cold front comes through too quick.

Impressive OKC sounding

http://weather.admin.niu.edu/chaser/tempgif/21798.GIF

Future model runs will tell...

 

[samuel stone]

with the 06z run of the nam now coming into 18z wed. its very nice to see such a strong arching dryline this far west(finally to the west of my location) by 18z dryline is surging to approx. a hobart to waynoka to kinsley to wakeeney line. with a potent negatively tilted trough moving right over the moist sector we havent had this much this year in the plains. 4-14-11 is about the only time i can remember. we have good backing of the surface winds ahead of most the dryline and plenty of forcing from the neg. tilt trough. but the main problem im seeing right now is backed 500mb winds becoming nearly parralel perhaps to the dryline!(perhaps too hard of a neg. tilt?) this COULD wreak havoc on storm mode/evolution. honestly im just happyy to have a good moist sector overlapped by a strong trough at this point and maybe well get better veering in the upp lvls by 0z once the 12z nam comes out? all in all im pretty pumped by wednesdays prospects but im not a fan of such a lack of directional shear and up lvl wind
parrallel to the boundary. who knows tho i remember 5-22 and 5-23 of 2008 looking alot like this and its safe to say it worked out pretty well on those days!

 

[samuel stone]

the 12z nam seems to resolve the backed 500 mb wind issue for me. with SErly surface wind through north central ok and south central kansas staying well backed up to 850mb and then veering just enough in the mid levels id say were doing ok in that department. and i love the divergence of the 300-200mb winds its textbook if you ask me. without getting into anymore detail as were still 84 hours out... im just gonna say that the 12z nam is currently progging what i would consider a synoptically evident severe weather outbreak with tornadoes being good probability. dont wanna go to crazy yet tho. thoughts?

 

[Michael Riedl]

Somethings I like about this set up is the sharp dryline suggesting decent surface convergence that could help break what little cap there is by the early evening. I like how the 850's as you said are for the most part Due south. The NAM is quite a ways further east with the dryline than the GFS at this point and it is much sharper at this point than the GFS. Another good thing for this day is the 700 MB temps AOA 5-7C, should not have to worry about a cap by 0z Thurs.

The 12z NAM also has the mid level jet streak much stronger than the GFS as it crosses the dryline. I wish that both models would nudge those stronger areas of wind over the dryline for even better speed shear but that might be wishful thinking.

Things I do not like, directional shear, but its plenty good enough for tubes across the Dryline (3/28/07? though speed shear was better that day). Pretty Anemic 200-300 MB winds across SC KS, but across NC to Central OK they look pretty good.

At this point along I -35 or even a little further west then I-35 in NC OK looks like a safe bet for severe weather, possibly even tornadoes.

 

[Trey Thee]

I'm holding my comments for one more model run...but at this point the setup for Weds is looking pretty good. There are some issues that wont be resolved until closer to the day...but conditions at this point look favorable for at least a few tornadoes in OK and a few more in KS. Helicities are good not great, crossover is adequate but nothing spectacular at this point. CAPE is again respectable but nothing over the top.

I'm anxious to see how things unfold over the next 48 hours. It definitely appears that SVR is likely.

 

[Ken Johnson]

Strangely, the 12 and 18z NAM keeps a bit of cap in place with little to no precip showing. Up. I my opinion, forcing looks good along with that sharp dryline. 700 mb temps are not as warm either. GFS still shows more storm coverage, which makes more sense.

 

[Darren Wilson]

00Z NAM shows an improved upper level wind field from yesterday morning's 12Z run. With the negative tilt, upper forcing shouldn't be much of a problem. Combine that with impressive directional shear profiles, manageable LCLs, and good instability, this day could shape up to be fairly active. If we can get some right splits, which looking at hodographs shouldn't be a problem, we should be in business along the dryline in Western OK. Here's to hoping this model verifies so we can finally have a day with supercells in the "right" side of Oklahoma. I will be checking the GFS shortly.

 

[Andrew Stoller]

Wed. looks impressive if you ask me. Strong negative tilt southern/main portion of western states trough finally ejects out over a moderately unstable warm sector characterized by 60+ degree dewpoints. 2 areas of play look good - north central KS east of the surface low at the triple point, or the southern portion of the dryline in W central OK down to northern TX where 500 mb flow is more south westerly and directional shear is a bit better. Soundings show a bit of an 850 mb cap further south, but forcing aloft should help initiate some tail end type storms along the southern extent of the dryline.

 

[Chris Wilburn]

Wed. looks impressive if you ask me. Strong negative tilt southern/main portion of western states trough finally ejects out over a moderately unstable warm sector characterized by 60+ degree dewpoints. 2 areas of play look good - north central KS east of the surface low at the triple point, or the southern portion of the dryline in W central OK down to northern TX where 500 mb flow is more south westerly and directional shear is a bit better. Soundings show a bit of an 850 mb cap further south, but forcing aloft should help initiate some tail end type storms along the southern extent of the dryline.

I agree with getting as far south into SW OK/NW TX as you can. 500mb winds like you mentioned are more southwesterly creating greater directional shear. I love the very sharp dryline creating nice convergence. CAP doesn't seem to be a major issue so that's a plus. I am currently thinking Lawton to Wichita Falls. The finer details will come into play with later model runs, but looks like a nice chase day for sure.

 

[Michael Riedl]

New 12z NAM is in and It likes SC KS, as do I. The LLJ in this particular area is stronger and SErly as well, helping to increase Lower Level Helicity. 12z NAM has a 0-1km SRH max of around 200 right over the ICT area. LCL heights in this area will be manageable. EHI Max in that area. I'd like a little stronger 250-200 MB winds with this area but I'll take my chances with a much stronger LLJ here than further down the dryline.

Hodographs in this area aren't necessarily amazing but I am hoping the lower level Turning of the winds will help produce a tornado in this area.

Right now I'll probably start out in Pratt as soon as class gets out around 2.

 

[Greg Blumberg]

From a quick look at the recent 09 UTC SREF, my biggest worry for Wednesday is the availability of good helicity. Everything else looks good from the perspective of a nicely negative tilted trough, SBCAPE around 2000 J/kg, and a good position of the surface low. I'm seeing effective shear of 40 knots and issues with lower than wanted helicity values. Good helicity isn't depicted from the SREF's 0 - 3 km helicity probabilities. It's depicting low probabilities of the 0 - 3 helicity even reaching over 200 J/kg. What's even more interesting is that the 12 UTC NAM is depicting some subtropical jet interactions with our shortwave.

I'm tying the low helicity value to an uncertainty of the wind field forecast. What's odd is that the SREF (and 12 UTC NAM for that matter) has a mean 1000 mb Colorado low, but we're dealing with a negatively tilted trough! One would expect a much deeper low given the negative tilt and jet streak. I think that the helicity and shear values will be something that will be figured out the day of, rather than forecasted. Maybe I'm misdiagnosing a feature as I'm doing this analysis really quickly, but something doesn't smell right with the recent model solutions. I'm looking for different kinematics on Wednesday.