5/3/06 FCST: OK/KS/TX

[nickgrillo]

There looks to be a pretty nice setup forming on Wednesday (as well as Tuesday)... A warm front should exist over portions of northern OK/southern KS by the afternoon, with > 65 tds progged south of the frontal zone, yielding very large sbCAPE (e.g. 2500-3500 j/kg progged by the NAM) with the GFS being just as aggressive with the low-level moisture. The one problem may be relatively weak upper flow (e.g. 40-50kts at 250mb, as progged by both the NAM and GFS) but the 0-6km shear is excellent, given the deep-layer veering flow across the moist sector. Forecast soundings from the region show deep moist layers across the region, with several soundings in southern KS (along and south of the boundary) showing awesome ("fat") CAPE profiles, with some nice low-level curvature in the hodographs (albeit relatively meager SRH accumulating in the lowest 0-1km AGL in most spots). Both the NAM and GFS initiate precip along/south of the front by the mid-afternoon, with most of the forecast soundings showing sbCIN eroding effectively to aid deep-layer ascent of moist air.

I think both Tuesday and Wednesday have some pretty good potential (with northwesterly flow aloft and backed surface flow yielding strong 0-6km shear and rich low-level moisture augmenting to progged CAPEs of > 3500 j/kg to induce a supercell threat on both days), and I plan on leaving tomorrow afternoon for KS (maybe I'll get lucky and see some convection on the way west tomorrow evening LOL). I have to say that both days look equally as pleasing (very strong-extreme sbCAPE + large 0-6km and nice low-level shear in both cases for the most part) in terms of both thermodynamics and kinematics.

 

[nickgrillo]

Wow... Things have changed dramatically... The latest NAM and GFS show even weaker mid-upper flow across the moist sector, with relatively weak low-level shear as well (particularly in the lowest 0-1km layer) near the surface boundaries in western OK/eastern TX panhandle. The NAM still shows > 3500 j/kg across western OK, but the best sbCAPE is removed from the best low-level shear, with 300mb winds quite weak across the region. The forecast soundings across southwest OK show very large sbCAPE (e.g. 4000 j/kg) but small and relatively straight hodograph structure... A bit further north, towards Woodward, low-level shear is a bit stronger, but sbCAPE is weaker.

There is still enough 0-6km shear to pose a threat for supercells -- particularly near the dryline/warm front in western OK by the mid-late afternoon as sbCINH erodes to allow for surface-based development. However, I am quite upset by the degree of low-level shear... I just hope the day doesn't go to crap. I decided to sit today out due to the incredibley long drive from Detroit (and getting off to a late start at 6pm edt and not getting to Kansas City until around 7am cdt). We'll see...

 

[Kenny Drake]

I really should be studying for finals, but I think this will be the last chase opportunity in the southern plains for me this spring (I go back to Minnesota May 14th weekend.. not that MN has bad chase terrain.. anyways). In response to previous post, the Skew-T forecast sounding for Chickasha (KCHK) doesn't look too bad at all, and dewpoints at surface are in the upper 60s. However tonights convection will probably mess the whole situation up for this area, and I'm betting the best vertical profiles might be farther south, but that all depends on the OFB which I will investigate tomorrow morning once it is set up. In fact, OUN's forecast sounding doesnt look too bad either. Looking at the 00Z NAM run I would target Altus which seems to be a great chaser city (good Wifi, and surrounded by good chase terrain). 500mb winds are lacking, but I personally don't think that is a requirement if the directional shear is there. Roads are nice too, with Hwy 62 running E-W, and 183 and 283 running N-S nearby. All in all, to summarize the main feature that will decide the outcome/location of tomorrow will be the OFBs from tonights convection. Basing off a suspected OFB near the Red River I wouldn't be surprised to see my Altus target shift southwards into Texas.

 

[Jeff Snyder]

I suppose it all comes down to (a) how strong the midlevel flow is and (B) how the environment deals with the ongoing convection. Personally, I don't see too many disimilarities between yesterday (May 2nd) and today (May 3rd), just some minor differences in threat area. Again, relatively strong CAPE and weak deeplayer shear may spell quick transition to HP. The lack of a cap on model guidance again suggests that we may see numerous storms by evening, with cell mergers and interactions. I'm busy again tomorrow, so I'll have to see at least 35kts on the Tucumcari profiler to chase tomorrow. Of course, it'd be nice to get mid-60s into western OK anyway, but that's uncertain given the broken squall line from se OK to northeastern Mexico (it's dissipating in many areas now, however).

 

[Kevin Scharfenberg]

Today looks like a bust to me. Flow looks weaker throughout the depth of the troposphere with shortwave ridging overhead. That also means a stronger capping inversion. The shallow moisture that came back yesterday got clobbered by the convection, with very poor 12Z moisture profiles except at BRO/CRP. At this hour, I'm quite skeptical we'll see anything worth writing home about in the MDT risk area. Instead, I expect a few storms way back in eastern NM in the upslope region and a thin line building down the front into southern Kansas.

 

[Kenny Drake]

Man I wish we could have a much stronger capping inversion in place, today would be a great chase day if it was so with very slow storm movements. Anyways, yea 500mb winds are lacking and that is the one problem. I will probably stick this one out, a little too far for me (probably end up near Childress) and I have more important things to do. Anyways, If I was going out I would target Altus and then figure out where to go from there. I don't see too much of an issue with moisture return, we will see low to mid 60 dewpoints which is adaquate but once again the main threat to the chase will be the quick switchover to a MCS. Wow today looks like yesterday all over again, maybe a few quick naders but thats it. However still a plus, rain to areas that need it desperately.

 

[Angie Norris]

Lawton looks to be a decent starting spot if one could get out today. Like Kenny said, 500mb winds are definitely on the weak side, as are the surface winds, but CAPE is progged to once again be in the 3000 J range and Tds progged in the 60s, so things aren't totally shot . If it wasn't for those wonderful things called finals looming next week, and that evil thing called work, I'd disappear to Lawton, keeping options open to run to Hobart if need be.
Good luck to those who will get to give it their best shot!!
Angie

 

[Brian A. Morganti]

My daughter and I arrived too late on the scene for yesterday's (5-2-06) storms near CDS, but it looks like we may get a repeat perfomance today. The 00Z ETA has the triple point progged to be over the SE TX PH by this evening and SFC winds should become a bit more backed with time. A Theta-E ridge is depicted from SW OK westward towards Tulia and southerly surface winds will be converging in this area beneath a weak to moderate 500mb WSW flow, but CAPE values are certainly adequate for vigorous convection. Moisture return may be a concern by the time of CI, but the tornado threat could increase as the the storms creep eastward into deeper moisture and begin interacting with OFB's. A quick check of the 12Z ETA reveals no improvement of the 500mb flow, in fact I don't like the subsidence depicted by the converging winds on the latest models which may mess up an otherwise chaseable event. But I'm here on chase vacation so it's still a GO! CI Target: Northfield, TX We'll leave Clinton, OK shortly and head towards CDS and evaluate from there. Good luck to all who head out today! --

 

[Mickey Ptak]

Well the 500mb winds look weaker than they did yesterday IMO and the storm just west of Childress yesterday simply creped along so I can only imagine how slow these puppies will be moving today.

I still think we could see a couple of tornadoes and landspouts today with no questions asked. After our lucky core punched tornado yesterday I would be hard pressed to say there won't be any tornadoes giving the amount of CAPE an the lack of capping. Granted you will be chasing some nasty outflowish in nature storms which will probably merge together time and time again but if you find yourself in the core you best keep your eyes moving all around the entire time...

We will be leaving between 12-1:30 this afternoon to Childress once again. Good luck to all and be safe.

Mick

 

[Gabe Garfield]

Today looks like a bust to me. Flow looks weaker throughout the depth of the troposphere with shortwave ridging overhead. That also means a stronger capping inversion. The shallow moisture that came back yesterday got clobbered by the convection, with very poor 12Z moisture profiles except at BRO/CRP. At this hour, I'm quite skeptical we'll see anything worth writing home about in the MDT risk area. Instead, I expect a few storms way back in eastern NM in the upslope region and a thin line building down the front into southern Kansas.
[/b]

I think the apparent poor moisture depth on the FWD sounding is due more to dry air aloft mixing with the moisture at the surface than with a widespread thin moisture layer. I can't imagine that the upper 60s/low 70s Tds in the DFW area now are only skin deep (especially if you look at the moisture depth on last night's FWD sounding). I imagine those higher Tds will slowly advect westward, but whether or not they will reach the target area in time remains to be seen. If they should arrive, I would expect a similar threat for tornadoes as we saw yesterday (and perhaps a bit higher should the upper 60s get there).

As far as the kinematic profile is concerned, White Sands profiler showed a mid-level speed max of 40 kts that entered at 9 UTC and exited around 15 UTC. If this should propagate eastward over the target area, a considerably higher threat of supercells would exist (Eta hints at the presence of a speed max on its 12z run). Also, the DYX VAD wind profiler shows a fairly strong LLJ (on the order of 35 kts), so that might help moisture return a bit. The low-level flow will be fairly paltry by this evening (according to the Eta/RUC), but a baroclinic boundary and some strong instability could offset that a bit.

Gabe

 

[Stan Rose]

The NAM likes the area south of Pumpkin Center (i like that name, sounds cooler than Lawton ) but be cautious about the NAM, it's currently 3-6 hours too slow with the front--northerlies cover the top half of the TX panhandle. This has me nervous, since i leave tomorrow afternoon and dont feel like driving too far south or east!

 

[Dan Dawson]

I really don't like the weak flow aloft. It looks similar (or possibly even worse) than yesterday, and while yesterday's wind profiles over the region were obviously sufficient for supercells, they were all messy HP's. The only hope in this department is if, as Gabe mentioned, that belt of slightly stronger midlevel flow of 30-35 kts seen on the White Sands profiler were to make it intact over the target area today, or if something like the Eta forecast of 35-40 kts at 500 mb over central OK were to verify. Otherwise, 12Z soundings show some decent lapse rates in the midlevels still, so with continued heating some good instability by late afternoon seems a good bet. At this point for me, it's a wait and see approach. I went out yesterday, so I'm not too keen on going out to chase another marginal setup, but we'll see. I'll be watching the profilers to see if we can get some better wind fields.

 

[Bill Tabor]

Looks really weak to me for tornadoes in SPC's 2% to 5% area. RUC obviously has more optimistic view, but isn't anything too special. SPC forecast must mainly rely on leftover boundaries to make the difference since by NAM/RUC respectively sfc wind is nil/low, 850 nil/low, 700 nil/low, 500 low/low, 300 low/low. Both NAM/RUC indicate a bit of dryline bulge toward the CDS area but amount of uncapping is questionable. 4.5km NMM WRF shows precip breakout 22z sw of CDS which probably will happen. I expect primarily hail storms of HP variety with very slow / no movement and very low chance of torns (say <= 2%). Probably there will be at least one tornado logged but not sure it will be chaseable and may be wrapped up like most yesterday were. Almost all NAM/RUC tornado forecast parameters are showing 'no' to 'low' out that way toward CDS. EHI at 18z centered central Tx and by 0z nearer DFW. Probably other hail storms will be scattered around Tx today. Probably like yesterday RUC will look a bit more favorable on next couple of runs. Right now I don't see anything making me want to leave AUS.

EDIT: You folks mention highly uncapped enviroment but I don't see it. Only NAM shows uncapped in small area of SPC's region at 0z. RUC has it capped:
http://www.rap.ucar.edu/weather/model/disp...&hours=hr06hr12
http://www.rap.ucar.edu/weather/model/disp...rs=hr06hr09hr12

With very little in way of short wave, and low wind from 300 down sfc convergence / upper divergence will be low. Will mainly have to rely on diabatic heating and upslope flow of caprock.

 

[Kevin Scharfenberg]

A review of the 12Z raobs, morning visible satellite and surface obs shows the deep moisture continues to be confined south and east of the D/FW metroplex. The moisture has been unable to return northwestward without mixing out...look at the strong westerlies observed just above the surface on the Purcell/Vici profilers and FDR/TLX VWPs. The deep moisture appears instead to be confined to a channel from roughly Austin to Waco to Texarkana and Little Rock. Short range model guidance suggests the winds just above the surface will eventually back and weaken, but not until closer to 21Z.

I don't see how the true deep moisture can make a run from the metroplex all the way back to west of 100 degrees longitude in 6 hours, particularly with no strong south/southeasterly low level jet. Instead, I expect skin-deep 60 dewpoints (much like yesterday, but a degree or two lower). Any storms that do go up out in the panhandle should be high-based and quickly produce gusty, cold outflow. Add into the mix weak shortwave ridging overhead, diffuse or nonexistant low-level boundaries for focusing initiation, and weak steering winds, I still don't expect much to write home about today.

The deeper moisture plume should slowly return north late this evening and meet up with the cold front moving through Oklahoma, so would also expect storms building down the line in Kansas to eventually overtake much of Oklahoma after dark.

 

[Bill Schintler]

Target:
Plainview, TX

Timing:
Storm initiation 5 PM CDT:

Comments:
Supercell storms capable of hail to 2â€￾ and winds to 70 mph. An isolated tornado threat will exist where storm scale interactions with pre-existing boundaries occur. By early evening, storms will rapidly evolve into a multicell complex.

Discussion:
UA analysis shows a broad trough digging in the SWRN CONUS, with two ULVL disturbances, the first lifting through NM followed by a second one entering WRN AZ. At the SFC, a synoptic CF extends NEWRD from low pressure centered just W of HOB; along a PVW to HHW line, to another low near GAG. Numerous outflow boundaries were left behind from last night’s convection. Radar data indicates an OFB along an LBB to 30 miles N of CDS line, while the FDR radar site indicates a N/S oriented boundary from LTS to CSM moving to the W at 5 mph, and another SW/NE boundary just E of CDS.

Later this afternoon, the CF will begin to lift back to the N as a WF while a dryline pushes E into the area. Expect convective initiation to take place near the intersection of these two boundaries near PVW as convective temperatures between 90 and 92F are reached and SFC convergence and forcing increase with the approach of the lead ULVL wave. MLCAPE’s should exceed 2000J/kG while deep layer shear will be acceptable, reaching 40 kts on top of 10 kt backing SFC winds.

- bill