5/9/2006 FCST: OK/TX

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Tuesday looks to be an almost definite chase day, at least in my opinion... With strong deep-layer veering and at least modest flow throughout the troposphere (with GFS being stronger with the overall flow), 0-6km shear profiles will be quite favorable for organized supercells, particularly wherever the warm front exists (likely somewhere in northern TX or southern OK) where strongly backed boundary layer flow is forecasted. The current NAM shows 200-300 m2/s2 0-3km SRH across northern TX along the warm frontal boundary by the mid-afternoon, with convergence in the lower levels likely being strong enough to initiate deep convection. The NAM shows plentiful instability across the warm sector, with 4000-5000 j/kg sbCAPE being supported by the very moist and heated boundary layer by the afternoon across OK and TX (and strong CAPE also spreading into southern KS). I would like to see low-level flow a bit stronger, but the modest flow does support very slow storm motions ahead of the surface low. So, overall, extreme instability and strong deep-layered shear forecasted to develop across the warm sector on Tuesday virtually makes it look like an awesome chase day (although I hope I don't have to chase northeast TX or southeast OK LOL), at least in my opinion.
 
I am a little worried about the lack of veering between the surface and 850 millibars on Tuesday 0Z, because this will severely hamper supercell potential. Eta breaks out precip along a warm/stationary front stretching roughly from Woodward, OK to Tulsa, and the deep-layer shear will be supportive of supercells with 35 knot westerly flow at 500 above 10 knot easterly flow at the surface. Potential overnight convection may strengthen the surface front, but I still am rather hesitant about the 850 wind forecast. I have a final in my Radar class the next day, so I'm not exactly hot to chase a marginal setup, but we will probably see some changes in the next couple runs.
 
Tough tough forecast tomorrow.... Previous model runs (before tonight's 0z runs) showed strong easterly flow on the cool side of the front (near I40 or the Red River, depending upon specific model and run), with 3000-4000 cape on the cool side. The 00z runs almost unanimously agree that a sfc low will slide across OK during the morning, weakening as it moves eastward. Meanwhile, pressures may drop in west-central TX. This surface pressure evolution leads to severaly veered flow south of the front (as the first low tries to moves into AR), and northeasterly or northerly flow to the north. This is doubly-bad -- not only do we not have backed flow in the warm sector, but we have way too northerly flow in the cool sector. Luckily, the juice is here, so CAPE won't be a problem. Forecast hodographs are quite punishing, however... Instead of strong low-level and deeplayer shear on the cool side of the boundary with strong to extreme instability, we're dealing with a cold-air advection regime (backing with height in the 850-700mb [depending upon the specific location]). To the south of the front (like Ardmore and McAlester), we have extremely veered flow (SW sfc winds)... 500mb flow isn't particularly strong, so this veered flow results in meager 0-6km / deeplayer shear profiles to the south of the front, with low-level pretty much nil. The hope is better farther east (look at the Fort Smith 21z / 21hr forecast sounding), with strong-extreme CAPE and much better looking hodographs. Unfortunately, I have an 8am final on Weds, so I can't go too far east. In addition, that's horrible chase territory.

So, the models took a nose-dive for the setup tomorrow across central OK. If the 0z runs verify, the best tornado threat looks to be from extreme eastern OK into AR.

Of course, after this, we have a high-amplitude trough in the east, with a surface high making a run for the Gulf. IT may not get there, but the models agree that the next surge may wipe it clean... But, that's another thread...
 
As I was driving back from DDC to Norman (thats a lot longer than I thought...) I couldnt help but notice the massive amounts of juice available for today. Too bad the winds are going to be about as bad as possible. I won't discuss it since Jeff pretty much said what I was going to. *HOPEFULLY* We get a OFB somewhere over central OK to back the winds south of it. Westerly 500mb winds should keep the cells from riding into the cold pool north of the mentioned OFB (if we get one...) but if there is a northerly component it could have a disasterous affect on the inflow. 18Z forecast sounding per NAM 00Z is horrible with SWerly surface winds. If we can get the winds to back at the surface, tornadoes are almost a definite with the amount of available moisture leading to very nice CAPE values (3000-4000J/kg). This also means very large hail...

SUMMARY for tomorrow: Plenty of juice, horrendous wind profiles... but might be fixed by OFB that should fixate itself somewhere across central OK, and finally.. a good chance the meteorological chase "zone" will come together in the worst chase terrain in the plains (SE OK/NE TX). What I'm hoping for is the low to hold itself farther west and a nice solid OFB across central OK leading to an easterly component to the surface winds.
 
TARGET: PAULS VALLEY TIME OF DEPARTURE: NOON Another marginal chase day IMO. PROS: An outflow boundary from last nights convection is progged to stall across southern OK. Surface winds have backed nicely over central OK. There is plenty of surface moisture to the south. A dryline bulge will extend along I-20 to the DFW area later today. Upper winds above 500 MB are sufficient. Relatively clear skies ahead of the boundary will assure a warm and unstable airmass. So what could go wrong? CONS: With too much moisture, heating, and weak winds below 700 mb I expect widespread convection and lots of HP's. I also expect this activity to move into the jungles of SE OK later today, so chasing is only going to get tougher as the day wears on. TM
 
I know it doesn't look favorable right now with north winds... but I am planning on a target in the western Panhandles. I am banking on upslope initiation at the nose of the incoming Rockies jet. There are lower 50s dewpoints still hanging on in the central PH with the better juice not too far east. Winds at Raton, NM are now east.... I expect cyclogenesis to continue in eastern NM which will veer the winds around in the target area to strong east component... the surface obs will be changing quite a bit today in the target area between 18z and 00z... A lot of sunshine will but the halts on current pressure rises as diabatic heating and subsequent diurnal pressure falls ensue... target Dalhart metropolitan area and surrounding vicinities.... this target is quite variable, so I will leave for Dalhart between 11am and noon and re-eval. There will be storms in this area... cold aloft, nose of massive upper jet... *mode* will be the main question of course...
 
It's looking like it may literally be a back-yard chase day today. This morning's early convection up at Tulsa has put down a sweet outflow boudary to work off of. I was originally thinking the Ardmore area, but may not have to go that far south. Will have to quickly look when I get out of my physics final, but I'm thinking maybe the Davis area for a starting point...and pray that I don't have to follow things off into the jungle. It's definitely going to be a messy chase with the HP hailers.
Kenny....yep, looking at the map it doesn't look like DDC is THAT far away :blink:
Angie
 
I don't have much choice other than to chase central/eastcentral and possibley southeast OK later today (leaving KS now with Darin Brunin and Dick McGowan), especially after the crap chase yesterday. The RUC and NAM still show a very favorable scenerio over the region (e.g. 4000-5000j/kg sbCAPE or even locally larger -- as well as strong effective deep shear and enough low-level shear -- particularly along warm front/OFB later this afternoon) with the RUC initiating precip over eastcentral OK around 21z. There is a lot of CINH to break for the release of surface parcels, but I think the strong insolation/low-level mixing (and deep BL moisture) will erode the cap sufficiently later this afternoon for the initation of deep convection.

I'm out...
 
In Woodward OK now heading for a spot w of OKC for more data. I figure a spot about 50 miles sw of OK might be ok, or even more west. The 12z eta seems to hold that weak bulge there as the new low tries to form. So wherever that convergence max moves to. That second boundary seems to have to weaken if the sfc flow is progged to veer from ne to e in w OK. Hopefully there is enough convergence near that area to overcome the cap. I guess I'm thinking of the area from Bridgeport to Anadarko.
 
Satellite and surface obs indicating a decent scenario this afternoon for the area generally S of I-40 and just E of I-35, say triangle from Norman to McAlester to Ardmore. Backing of surface winds were a concern in some of the earlier forecast posts, but it looks like the surface low now around Lawton is doing a decent twist. Although the 500/850 crossover still looks anemic, ample directional shear at the low levels - with massive instability building under a strong but breakable cap - indicates this could be a rewarding chase day for those out. Good luck to all of you; PM me if you need any nowcast assistance.
 
Current surface map shows a very complicated set of boundaries over southern and central Oklahoma. I did a bit of hand analysis of the surface map, and it revealed a few things. First, an elongated area of low pressure extends from Frederick to south of Chickasha. From the low center, an outflow boundary extends in an arc from Frederick to north of Chickasha to Moore and then east to Wewoka to north of McAlester. Just to the north of this boundary, a weak cold front extends from Mangum to Weatherford to west of Kingfisher.

My best guess is that the low will continue to elongate as the lead wave departs and the approaching upper wave induces lee troughing in E NM/W TX. Also, mixing should cause the surface flow south and east of the low center to veer. The low continues to slowly propagate ESE, so based on its current location and motion, I would expect the low "center" to be between Ardmore and Pauls Valley by peak heating. The outflow boundary should also sag a bit further south. Thus, my target for now is Asher, Oklahoma in southern Pottawatomie county where I expect the intersection of the low and the outflow boundary to be when the show starts (storm mode might be an issue).

Gabe
 
Looking at the pressure trends on the OK mesonet, it looks like the low currently SW of OKC is filling and moving east: obviously not the most favorable scenario. There are significant pressure rises all across central and western OK right now, with pressure falls in parts of eastern and northeastern OK. This tells me the models more or less had the right idea in weakening the surface low and moving it eastward during the day. The low-level wind fields also look rather anemic. However, given the placement of the outflow boundary, I still think that storms that interact with the boundary could have decent tornado potential, even if the surface flow south of the boundary does indeed veer later, as seems to be the model consensus, because low-level shear should be a maximum along this boundary. Furthermore, given the strong lateral shear along the boundary, some decent ambient vertical vorticity will already be in place, and given the extreme instability, this could aid in tornado potential as well. My target would be east of I-35 anywhere along the I-40 corridor.

Dan
 
Chase target:
Talihina, OK (40 miles east-southeast of McAlester).

Timing:
Convective initiation 5 PM CDT.

Comments:
Conditions will be favorable for all forms of severe weather today, including large tornadoes. Unfortunately, this is poor chasing terrain, as this area has a poor road network along with heavily wooded hills.

Discussion:
Synoptic low pressure is located near FSI with an outflow-enhanced boundary extending east of the low and oriented just south of I-40, which shows up well on visible satellite imagery and radar. Surface convergence and backed flow along this boundary will provide the focus for severe weather later this afternoon. Extreme instability will couple with marginal shear parameters, with the thermodynamics partially making up for the kinematic parameters.

The airmass has been somewhat worked over by the morning convection, and area soundings show a moist layer on the order of 75mb deep with a mean mixing ratio of 16g/kg beneath an EML with mid-level lapse rates of 9C/km. Guidance is a bit over ambitious with regard to SFC moisture return, and I will adjust late afternoon SFC dewpoints down by two to three degrees F. Nevertheless, SBCAPE’s should locally exceed 6000J/kg with MLCAPE’s (100mb) reaching 3000J/kg. There will be a strong inversion between 850 and 900mb, resulting in convective temperatures in the 95 to 97 degree range. Although forecast high temperatures will be a few degrees shy of this, expect enough SFC forcing for initation along the aforementioned boundary as a mid-level wave now evident on WV imagery crossing the Red River slowly lifts north towards the area. Deep layer shear (SFC-6km) will only be on the order of 25 kts, however favorable hodograph curvatures will exist below 3 km as a 40kt H7 streak lifts over locally backed SFC flow.

- bill
 
I can't help but post this... several OK mesonet sites SE of Norman reporting Td's in the mid 70s!!!! There looks to be a "dryline" along I-35 from OKC southwards to RRV dropping Tds from mid 70s to low to mid 60s. I would expect initiation to occur along this, with the best tornadic potential to be where the OFBs intersect this boundary. Sattelite imagery already showing healthy Cu building in SE OK and abruptly ending along this boundary. It's really hard to tell if this boundary has to do with topography or not (SE OK is more vegetated, evapotranspiration will up the Td's a few degrees). It looks to be an OFB. Anyways as the day progresses I think the cold front will get wrapped around in TX it may wrap around eastwards and intersect the warm sector, cutting off the dry-air intrusion which may spell certain changes in storms. If I was chasing I'd be following the OFB as it moves southwards throughout the day. I would probably target McAlester at this point and be prepared to move south.
 
Currently setting in Ardmore enjoying a coke blak. Temp where I am is 93/70. I am on the leading edge of some agitated CU but am thinking I may need to go further East or even NE. It looks like moisture is getting pulled around the low to the West ad wouldnt be surprised to see something go there later on. I mmay be too far SW but we shall see. Looks like OFB intersect FRONT ALONG I-40 just East of OKC or slightly SE. Pauls valley up towards Asher and Ada may be a good spot. Lets hope something goes more toward I-35 with good cell coverage and better roads and visibility. Mcallister might be a good spot as well but I hate chasing around big lakes.
 
Currently sitting in Stroud at the McDonalds.....getting ready to drop south toward the Ada area where it is 88/72 and winds are slightly backed east of here. Outflow boundry situated right along I-40 as Jason mentioned east of OKC. Getting ready to head back on the road and head south towards the Ada area or just south of interstate 40. Dewpoints in the low 70's with very large CAPE values leads to some hope.........winds dont look great but oh well they may not need to.......will get some nice structured sups. out of this at least.
 
Atmosphere is pumped and primed...ready to explode!

I would not be suprised to see a signficant Tornado along the east
to west boundary in se OK with over 70 dews, CAPES over 5000 J/Kg,
weakening cap, increasing mid level winds on the Purcell profiler
at or just above 500mb at 40 to 50kt.

With that much CAPE lots can happen, especially with that
existing boundary!

Good luck to all chasers down there, and stay safe, drive
carefully, should be a zoo of people.
 
Triple point appears to be over Norman right now. Cold front just to the NW with SE winds being reported per Mesonet @ 2:55pm. I'd expect this boundary to move SSE as the day progresses. Looks like several 500mb shortwaves will move through, one of these will probably be the catalyst to initiation due to the strong capping inversion. 1900Z OUN sounding shows a mess below 850mb, not sure what to make of it. CAP appears very weak per the sounding with only a very slight inversion near 850mb. I'd expect initiation shortly.
 
Currently sitting outside the Days Inn off I35 exit to Pauls Valley. 89 deg, and wind out of the south about 10 - 15 mph. A lot of juice in the air. Latest from the spc suggests cap may delay initiation until later afternoon early evening.
 
I'd be careful about the 19z oun sounding... it looks a little suspicious. Regardless, note that OUN has kept the moderate risk for SE OK this afternoon and evening... Such a deviation from the SPC occurs occassionaly. Current satellite shows enhanced Cu along and just south of the cirrus patch moving over the western OK metro area right now. Initiation may be imminent, but not sure how many storm's well see. FSM VWP is nice. Gotta go.
 
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