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

[Brian McKibben]

I think the West-Central KS area will have the best tornado potential tomorrow. I am not concerned about the unidirectional shear. The speed shear is good enough.

A good example for similar situations in KS regarding winds is May 22, 2008. Also, May 23, 2008 was very similar to the 22nd, except it had more tornado reports.

http://www.spc.noaa.gov/exper/archive/events/080522/index.html

I am concerned about the subsidence west/central OK due to the potential MCS over central/eastern OK earlier in the forecast. The 12z SPC WRF has the dryline much further to the west than before. It looks like storm will fire along the OK/TX border north of I-40 all the way to the triple point.

 

[Mark Meyers]

I am a bit concerned how the models may be underforecasting upper level wind fields. As in the case of the May 3, 1999 outbreak...which in no way I expect for this event...observed wind data from profilers need to be watched closely tomorrow. Looking over the Storm Prediction Center Forecasting Issues Related to the 3 May 1999 Tornado Outbreak showed how the ETA was under estimating upper level wind fields that let forecasters in part to stay with the slight risk until consecutive categorical risk upgrades were made in the 1630 and 2000 UTC Day One Outlooks.

EDIT...I would also add that hints from SPC and NWS FWD seem to be indicating the southern targets...ie SW Ok and perhaps the northern half of North Texas west of I35 could be a player by late afternoon...quoting from NWS FWD

"ALTHOUGH THERE WILL CONTINUE TO BE CONCERNS ABOUT
CLOUD COVER...INCREASING MID-LEVEL WINDS WILL FORCE THE DRYLINE
EASTWARD...PERHAPS AS FAR AS WESTERN EDGE OF CWA BY MIDDAY.
SHEAR IS NOT EXTRAORDINARY BUT WOULD FAVOR DISCRETE CELLS. AS THE
DAY PROGRESSES...BACKING SURFACE WINDS AND INCREASING SPEED SHEAR
IN THE LOWER LEVELS WOULD CREATE AN ENVIRONMENT FAVORABLE FOR
TORNADIC SUPERCELLS FAR FROM THE SURFACE BOUNDARY.

I will be watching this one

 

[Greg McLaughlin]

I am a bit concerned how the models may be underforecasting upper level wind fields. As in the case of the May 3, 1999 outbreak...which in no way I expect for this event...observed wind data from profilers need to be watched closely tomorrow. Looking over the Storm Prediction Center Forecasting Issues Related to the 3 May 1999 Tornado Outbreak showed how the ETA was under estimating upper level wind fields that let forecasters in part to stay with the slight risk until consecutive categorical risk upgrades were made in the 1630 and 2000 UTC Day One Outlooks.

It has been noted here and elsewhere, and may be a growing concensus, that the NAM in particular is having initialization errors and may not be handling the overall setup very well. If the NAM is indeed correct, then tomorrow may very well be a very local/low-end tornado event. I am anxious to see 00z soundings and upper charts tonight as well as the 00z model runs. The 12z ECMWF has a 999mb surface low in southwest Kansas at 12z WED while the 12z and 18z NAM only have a broad 1004mb low at 12z WED. As stated before, the upper pattern would tend to favor the ECMWF solution over the NAM in regards to lee cyclogenesis.

I have a question which I am hoping someone knowledgeable can help answer. With the expected anti-cyclonic veering of the upper-level winds from 500-300mb (particuarly as you head north into Kansas), what kind of impact could this have on storm behavior and mode. I assume the likely result will be a tendency for splitting cells, with the more isolated right splits taking a more deviant northeasterly direction. It is my understanding this will likely increase storm relative shear. If storms have a tendency to constantly split, could this hamper mesocyclone organization/longevity?

 

[Logan Karsten]

If the NAM is indeed having initialization errors, then tomorrow could indeed end up being a solid chase day. Now that this discussion has been brought up, I have noticed lately that the day of the event, the NAM ratchets up the shear, which I found to be odd. It wouldn't surprise me if that occurred with this event as well. The 12Z GFS had much better shear along the dryline, which is pushing me back towards liking the setup for tomorrow.

 

[Greg McLaughlin]

Just a quick note, the latest experimental RUC going out to 11z WED has a 995mb surface low in southeast Colorado. It only makes sense.

 

[Greg Blumberg]

Greg McLaughlin, I'm happy to see some guidance coming on board with a deeper low. I do agree with Mark Myers regarding watching the wind profilers. As we've seen so far, guidance isn't being very helpful in the kinematic department.

Greg, I'm not sure about what the backing wind profile would mean for storm evolution and mode, but I'll give it a shot. Most of all the wind profile we're seeing with the backing is commonly associated with cold air advection, which is a forcing for sinking motion (given nothing else is forcing rising motion.) The sinking would decrease lapse rates and decrease our CAPE values. For the storm evolution, my guess is that not much would happen because the backing (or anticyclonic veering as you put it) with height isn't taking place in the lowest levels. The hodograph is curved in the lowest levels, which is where your storm is likely drawing parcels. The upper level storm-relative winds will matter though because you need to consider where and how fast your precipitation is being blown downwind from the updraft. My guess is (from the NAM) that right movers will dominate based on the curvature in the low levels, but I get the feeling they'll be high precipitation supercells. The precipitation will be blown off to the north.

 

[Jeff Snyder]

This is a case in which hodographs can be extremely useful. Most of the GFS and NAM runs from the past few days have shown a S-shaped hodograph. There is good curvature to the hodograph in the 0-1 km AGL layer, but some weakening of the flow above that and some backing of the flow in the middle troposphere results in largely S-shaped hodographs in southern KS and OK. In fact, it's quite possible that storm motions will end up resulting in significant negative SRH in the 1-3 km AGL layer. In fact, there looks to be greater negative SRH for a left-mover than there is positive SRH for a right-mover. Yes, that means that left-splits and anticyclonic supercells may indeed be preferred slightly over their
cyclonic counterparts tomorrow for much of the area. Ouch.

I've highlighted three storm motions (indicated by the stars) in an example hodograph from the 18z NAM valid tomorrow evening near Guthrie, OK. The black star is the Bunker's estimate for a right-mover. The blue and magenta stars are very rough estimates for storm motions for a non-deviant and a left-moving supercell, respectively. For a right-mover, there is some streamwise vorticity (storm-relative wind aligned along the local vorticity vetor) in the 0-1 km AGL layer, but it's almost entirely cross-wise above that (i.e. very little SRH in the 1-3 km layer). For a storm moving along the mean wind (again, that's just a rough estimate), there is some positive 0-1km SRH, but quite a bit of negative 1-3 km SRH. Similarly, for a left-mover, there's more negative 750m - 3 km SRH (actually, strongly negative SRH through 6-8 km AGL, though that air won't be a "part" of the updraft).

Also remember that the turning of the storm-relative wind vector with height can affect storm motion through the linear term in the perturbation pressure equation. Typically, for most U.S. cases when the storm-relative wind vector rotates clockwise with height, the vertical distribution of pressure perturbations is such that the updraft preferentially develops right of the mean wind, and thus we can end up with deviant motion. In this case, the storm-relative wind vectors may end up turning counterclockwise with height. This, combined with negative SRH in the 1-3 km AGL layer in many of the forecast hodographs / sounding in the area, may result in more intense and longer-lived left-movers / anticyclonic supercells...

In my experience, I have had very little success with tornadoes in environments characterized by S-shaped hodographs. We don't necessarily need to have a veer/back/veer vertical wind profile to get S-shaped hodographs, since the shape of the hodograph is also affected by the wind speeds through the troposphere (this is the reason why you can have unidirectional wind shear and splitting-supercells-o-rama even in a nicely veering vertical wind profile characterized by southeasterly winds at the surface that veer to southwestern or westerly aloft).

Edit: I haven't looked too closely at this event yet -- I will examine it when the 00z runs come in. In addition, I haven't paid much attn to the central/northern KS target since I don't think we'll be targeting that area. I mention this because, for all I know, there may be a sweet spot somewhere else with a better looking hodograph. However, the shape of the hodographs is a concern of mine tomorrow. I'll be out tomorrow no matter what, though, since, even with these hodographs, there's the potential for tornadic supercells.

 

[Ryan McGinnis]

The 0Z NAM makes the area near the triplepoint from Oakley, KS and points northeast along the stationary front look like a good alternate play to the dryline. Good 0-1km shear and enough instability to work with. The hodos, as mentioned previously, are still confused with winds backing a bit above 500mb.

Storm motions are manageable at around 25 knots, but the vectors could take them out of the warm sector pretty quick, especially if the backing winds above 500mb favors left splitting storm as Jeff mentioned. It's probably too much to ask to get a good front-rider.

 

[Royce Sheibal]

Here's my two cents before bed. I'll end up doing a re-target probably at 9am. Recent runs of NAM GFS and HRRR all have AM precip heavy over NE. I'm gonna try and stay south of what appears to be a small shortwave over central NE, and hope that I can find a discrete cell forming off of outflows. I wish I had the time to drive down to S KS, the area just west of Wichita is looking great on the NAM, as SRH's look better on this run. I'm probably just gonna get stuck under multicellular junk all day.

 

[Mike Johnston]

Continue to like the area right along the KS/OK border, albeit a bit further west now - roughly from Woodward, OK to Coldwater, KS. Last 3 NAM runs have been pretty consistent with the best wind crossovers in this area; just shifted west some. Also, notice there is a good hint of a dryline bulge in this area, deep layer shear looks pretty good and low-level CAPE is maximized. Also 0-1km EHI values of 4-6 represent a nice little bullseye on the run only 24 hours out.

 

[Andrew Stoller]

The morning precip in the OK panhandle is either going to totally work the air mass over near the KS/OK border, or if it clears out quick enough, might provide a localized convective boundary intersection with the dryline. That's the only iffy thing I see.

 

[Doug Drace]

Still think the OK portion of the DL will be just as good as KS this afternoon/evening...potentially even better for Discrete Tornadic Supercells. From the chatter so far, it will definately be the place to be if you want avoid the long lines of the chaser circus in the northern target area. Im thinking of the SW/SC south of I-40 area as the "Express Lane" to tornadoes, with "10 chasers or less" please I still think the upper wind profile south of I-40 favors longer lived supercells, without all the confusion of splitting cells, Hodo S loops, and wondering what those funky S-SSE winds above 500mb are going to do to storms in KS. My only concern in the southern target is NAMs slightly higher LCL's, and lower overall EHI's, but im pretty confident thats gonna work itself out by later in the day. I also like the CAPE forecast of 2000+j/kg throughout the OK portion of the risk. Hi-Res WRF is painting a pretty sweet picture for OK+KS this afternoon, so all should have quite a day no matter their location preference! Good Luck and Safe Chasing to Everyone Today!

 

[Trey Thee]

Doug what location is that sounding for?

 

[Doug Drace]

Trey its between Lawton and Duncan, OK

 

[Ryan McGinnis]

Noticed that SPC is saying what I'm sure a lot have been wondering - that the models are out to lunch due to not initializing all the crapvection that's potentially going to keep the warm sector from being, well, warm. The current satellite shot is not encouraging.

The big question is where, if anywhere, will there be enough clearing during the daytime to initiate convection? My personal target is still the WF along the triple point and then watch the satellite for signs that it's clearing anywhere. Since storm motion will be northerly, it'll be a lot easer to work south to catch anything that pops on the DL should the triple point turn out fruitless than it would be to rush north from the DL.