3/27/08 FCST: TX/OK

[Bob Hartig]

Today's 00Z GFS shows a 998mb low centered over the western panhandles by next Thursday evening. Looks like the possibility of at least a couple days of severe weather. I'll focus on Thursday, since I like what I'm seeing: SBCAPE of 1,500+ j/kg from central TX well up into OK, good deep layer moisture, southerly surface flow, ample 6k shear, etc. The one question seems to be upper level support, which atm appears marginal, at least if you go by the GFS. I'll let more knowledgeable voices than mine address that issue; I know enough to realize we've got six days to play with. Right now, I see enough shaping up to open up this forecast thread.

 

[Bob Schafer]

I've been watching this for a few days, but with the upper disturbance so detached it's looking like subsidence may prevail over the area of interest. The GFS is showing little/no precip where the instability is progged to exist as a result.

 

[Stan Rose]

Hi Bob. Dont think subsidence is an issue with a possible 991 low sitting over OK Thu. Deep moisture might be an issue, and the dry air/cap might be one reason GFS is not too convective, although not unusual for the GFS to have little precip with this scenario--id rather see little qpf than too much! Trough has been trending a little more amplified, though still too zonal for me to even consider a long drive east, since its likely everything will be pushed east pretty quickly. Still, with the insane amount of shear, could be interesting. Ill be surprised if something doesnt materialize.

 

[Adam Penney]

Take what you want in the "off-hour" GFS runs, but according to the 06Z GFS and to my semi-trained eye, it looks like the 992 low is pushing across the eastern TX panhandle and into western OK around 00z. It certainly looks like mixing and a capping inversion could be the issues with Thursday, however, I will certainly be keeping my eye on each run. This has potential IMO.

 

[Bill Tabor]

Doesn't look to impressive to me so far. Very zonal.

 

[John Cameron]

While the upper level setup is far from ideal, this looks to be one of those early-season event where one or two discrete cells on the dry line may "show off" for 15-20 minutes...assuming the moisture is there.

Since this will be a local event for me, I'll make time for it.

 

[Bill Tabor]

0z NAM shows very much zonal flow with very little amplification. 500mb winds are weak, 850mb are quite veered. Sfc winds in best area fall off and are very weak. LI's are somewhat reasonable up to -4 or so. The sfc low does some weird stuff though. First it is east by eastern OK, north Tx, AR and next it reforms by 0z in western Tx, but is still fairly weak with not that low a pressure. Precip forecast does show the slightest precip, and cape by 0z is somewhat free from cinh by 0z in a very small area.

Only area of interest for me really would be the area just south of the Red near SPS or DFW. Looks to me to be fairly lame so far. PVA is very mild due to zonal pattern. In that area I might expect to find up to a few storms mildly severe and possibly not elevated. Largest risk will be hail and possibly wind from higher downdraft capes. For SPC I'd go small area of Slight risk 2% with no to 2% chance of torns for the time being unless something changes.

Perhaps Wed is a better day. Maybe I'll take a look at it.

 

[Adam Penney]

Well the differences in the 0z NAM and the 0Z GFS are still quite substantial. The strength and placement of the Sfc low are way off. The NAM places it at 1002 and in SE NM and the GFS puts it a little deeper at 996 and in the panhandles of TX and OK at 0z Friday. Obviously that is a significant difference. Add on to that, the cold front placement differs significantly as well. The NAM has it surging through SE OK and NC Texas around 0z and the GFS still has it up in MO and KS. I am very much hoping that these differences will be resolved in the next 24 hours, so a possible target area can be better defined.

With that said, I am of the opinion that Thursday will only be marginal at best. Upper level winds do not look to be spectacular, but as I have learned, sometimes a storm or two can pop up in this evironment and make you wish you would have been there. Hey, its March and I have cabin fever. Im dying for a chase oppurtunity, so I am trying my best to be "glass half full". LOL.

Hopefull by this time tomorrow, we can better sort this out.

 

[Bob Hartig]

I'm not optimistic about how it looks with the latest runs. Going by the GFS, I see some marginal possibilities; the NAM, on the other hand, pretty much removes upper-level support. Either way, CINH looks pretty stout overall. No road trip this week--gotta remind myself this is still just March.

 

[Bill Tabor]

So far I doubt I'll be making a trip either. 12z GFS and WRF-NMM seem to still have different placement of the low and frontal area with GFS a bit further north into OK - front almost to or in KS. WRF shows it likely near or south of OKC. CINH is greater on the GFS as well, and with no mid level waves likely will be primarily relying on diurnal heating and frontal convergence to break the cap. 850's are still showing veered.

I have some interest in ADM to GLA. As I recall WRF forecast soundings 0z at ADM are near 125 cinh. Still possibly or likely capped, it seems to be closest to having any potential unless the GFS solution is more correct in which case it would be further north with less chance of convective break out except perhaps on or north of the frontal boundary.

Various composite indices based off the NAM do seem to like the area from GLA toward OKC particularly from 0z to 03z and even indicate the potential for tornadoes if convection occurs. I am a little pessimistic about that since forecast sounds don't show a lot of directional shear at very low levels.

I tend to agree with SPC's thoughts here at the moment, they are going conditional severe based on resolution of the models agreement.

 

[Evan Stubbart]

I think all we'll see tomorrow is some good hail and maybe a couple discrete cells fire briefly with nice structure before the front. I happen to be jumping on a plane to KS and Springfield, MO tomorrow AM so I'll be in the area with a nice rental car, and see what trouble I can get myself into

 

[Kenny Drake]

I guess this seems like an okay enough day to begin my Spring 2008 severe wx forecast discussions. First to note is what most others have already pointed out for C.OK and southward: the CAP. The environment should remain relatively undisturbed from today's. The 00Z sounding from OUN shows a WELL mixed layer up to about 850mb. 850-800mb will be the question tomorrow along with depth of moisture. Given the ~60F Td's in Oklahoma at the sfc as of 10pm CDT I'm hoping to see deeper moisture advected in during the overnight hours. The real question is whether we can see the pressure/ht falls along the high plains needed to back the winds up to 850mb across OK/TX. If this happens, which the NAM is kind of hinting at to a weak extent, then I think we can see an isolated supe or 2 along the dryline tomorrow afternoon. The 24hr NAM forecast (00Z 3-27 basetime) sounding for KOUN shows ~2000J/kg CAPE w/ CINH ~-5.4J/kg. Winds veer nicely with height, wind speed increases with height continuously up to the tropopause. I think that is rather optimistic at this point. In the end this is an event that must be played as it happens. I'd say by 12pm tomorrow we'll know what kind of cloud-cover we're looking at along with depth of the sfc-based moisture. If surface temps can make it into the low 80s in some locals tomorrow then I see the CAP being broken (isolated.) Not many places in the moist sector made it to 80F today in Oklahoma (if any) and this was under mostly sunny skies until sunset.

 

[Buddy W Bradley]

Just a quick update. The warm front has pushed north to near the Missouri River at mid day. We have considerable breaks in the clouds here in sw Missouri. The local NWS office has increased there hazardous wx outlook to include winds to 70pmh and hail to golfballs or larger. Looks like the front should start moving south and east as a cold front over the next couple hours as the vad profilers up north indicate. I would expect based on the conditions and the clearing and all. . supercell thunderstorms will be possible over e. Oklahoma, nw Arkansas, extreme se Kansas and w. Missouri between 4 and 6pm.

 

[Bob Hartig]

I was glancing at the RUC on my F5 Data software, and just out of idle curiosity, I pulled up the program's proprietary tornado parameter, expecting nothing. Instead, I saw a substantial bullseye centered on the OK/AR border for around 4 p.m. CST. Checking a couple other sigtor parameters also gave me readings, particularly the Stensrud. I haven't explored more deeply because, practically speaking, I can't do anything about it. But if I lived down there, I'd be on my toes.

 

[Kenny Drake]

I was glancing at the RUC on my F5 Data software, and just out of idle curiosity, I pulled up the program's proprietary tornado parameter, expecting nothing. Instead, I saw a substantial bullseye centered on the OK/AR border for around 4 p.m. CST. Checking a couple other sigtor parameters also gave me readings, particularly the Stensrud. I haven't explored more deeply because, practically speaking, I can't do anything about it. But if I lived down there, I'd be on my toes.

Yea the wind profiles are not bad at all for supercells today but LCLs are a tad high and of course the monster 800mb cap. The cap should be broken in eastern OK and points NE'ward thanks to frontal forcing. However, the cold front screaming SE is veering the winds at the sfc quite a ways ahead of the forcing. Watch those parameters drop as the forcing that will break the CAP approaches. Last weeks polar invasion into the south basically killed this system. I always wait for the storm system AFTER the one that brought in the polar air for any good amount of moisture. Soundings verify that the moisture depth is very shallow. Even without soundings the OK Mesonet showed nicely how shallow the moisture was this morning. 60 Td's in eastern OK down to 40's in western OK. Topography is quite useful for determining moisture depth when there is no dynamic forcing at the surface. I think next week will be a lot better, however that is a different discussion for a different thread.