04/03/08 FCST: TX / OK / AR / MO

[Brandon Lawson]

I am liking what I see from the latest 00Z NAM run. It strengthens the surface low to 997mb, while maintaining a very sharp dryline extending along the southwest oklahoma border down into texas, with mid to upper 60 dewpoints. The result is even stronger and more backed surface winds, along with 30-40 knot 850 winds out of the south by thursday evening.

As long as early convection does not interfere with the instability, and the models continue with this trend, I don't see how this doesn't turn into a significant outbreak of severe weather with tornadoes likely.

 

[Gabe Garfield]

After perusing the latest NAM I have to introduce a third scenario:

The lead wave depicted in the 00z NAM initiates elevated convection over central and northern Oklahoma. After this, the 850 mb winds veer to SW in response to the departing wave. Next, the main wave pivots through and backs the near-surface flow (due to the ageostrophic response to the deepening lee trough). In this scenario, the wave initiates convection, then suppresses it (due to subsidence in the wake of the lead wave) allowing surface heating and destabilization to commence, after which the main wave initiates surface based convection near the surface low. Likely to happen? I don't know, but it is an intriguing possibility.

Also, I must note that, from an analog standpoint, Wichita Falls, TX would be an excellent place to target (i.e., April 3, 1964 F5 anyone? B-)).

 

[Dustin Wilcox]

Per the 12km NAM, while there's always the entire DL to play, IMO this looks to be one of those easy target chases, as everything will focus and point towards one localized area (i.e. chaser convergence). While that focus point will likely change several times over, based on this evenings run, I would target the Hwy 70 and 81 intersection, Waurika OK far enough East that it doesn't rule out dropping south and intercepting something further South along the DL; plus this is where the 12KM initiates the storm of the day and rides the true WF ESE along the nose of a 50kt Southerly LLJ. Decent Hodograph by 03Z to the East of this area 3km EHI's Near 10...http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=NAM&STATIONID=KGLE

 

[Mark Farnik]

Believe it or not, I'm actually not unhappy to see that elevated supercells are progged to be occurring across central/eastern Oklahoma in the early morning hours on Thursday. As with any situation in which we're dealing with early morning junkvection, there is a question as to how this 'pre-show' convection will affect the atmospheric instability for the actual ' show' convection. In this particular instance, these 'pre-show' junk cells should mostly occur outside of the target area and be Arkansas bound before the noon hour and as such should have only minimal impact on the atmospheric instability in the area of concern. With this 'pre-show' convection also comes the perk of the outflow boundaries they generate. Any residual outflow boundaries from this early morning activity could very well serve as convective focusing mechanisms, and any cells that can anchor onto or interacts with one of these boundaries will likely have enhanced tornadic potential.
If I lived in Quanah/Vernon/Seymour/Wichita Falls, TX or Lawton/Altus/Chickasha/Pauls Valley, OK, given the consistency of the model runs and the setup they are showing, at this point I would be starting to be very concerned about Thursday's potential...

 

[BrandonWhittington]

As of right now, playing off the caprock in the panhandle is my guess....I do agree with Mark about the early morning convection and its potential effects on thursdays setup, but it might give us a few more boundaries to play with....

 

[Chris Wilburn]

The day 2 is out with a 30% hatched moderate from the southern half of Oklahoma into NW and NC Texas. Everything appears to be in place for a potentially significant outbreak on Thursday per the NAM. CAPE near 3,000 J/kg and dewpoints in the mid 60's will create very stable environment ahead of the dryline from SW OK into NW TX spreading east as the evening goes on. Wind shear is really nice as surface winds back very nicely with southerly/slight southwesterly 850mb winds and 500mb west southwest winds. Storms should be moving at a decent pace at around 40mph. Surface low of 997mb should be located in the NW Texas region. I would expect tornadic supercells from SW OK into NW Texas initiating in the late afternoon due to a weak cap. SPC on the day 2 mentions and uncapped unstable atmosphere so at least the cap should not be too much of a factor. The only problem I see that has already been mentioned is the elevated convection in central OK during the morning. If this doesn't affect SW OK into NW TX as far as cloud cover goes I think we should have a very nice chase day. The 00z forecast sounding for Wichita Falls is very impressive with -6 LI, 8.7 EHI and very high 0-1 and 0-3 helicity values. LCL heights are low with LFC heights near 1,600. I am sure a few things will change between now and then but everything looks good on tonights run of the NAM. Like Dustin mentioned earlier in the post this looks like a very easy target along the dryline. I would say anywhere from SW OK to NW TX looks like a really nice target with NW TX being more favorable and away from the cold front which may not even affect SW OK early enough to matter. Altus to Vernon looks like a good place to start. I will dry and keep myself far enough from the dryline to stay in front of storms and catch anything coming up from the SW.

 

[Dave Holder]

Looks as though SPC is going moderate for their Day 2, April 3rd forecast.

As depicted by the WRF, major low level turning occurs just east of a dryline bulge with CAPE values of 2000+ J/kg.

I'd say the possibility for large tornadoes does exist at this point, with a bullseye perhaps around the Lawton-Witchita Falls corridor.

 

[Kevin Crawmer]

Well to my pleasure the models are trending to the east a touch from yesterday. Like we discussed yesterday, the center of the threat did indeed shift more to the Wichita Falls to Ardmore area. The NAM is still less bullish in the Red River area and seems to be a little slower than the GFS. The NAM seems to be taking the CAPE/shear down a notch too from "Armagaedon" to just "severe outbreak" ranges. The GFS is still trending a little north and has been pretty consistent the last few runs in focusing things in the Altus to Wichita Falls area and points southward along the dryline.

I am intrigued by the area just ahead of the dryline bulge and east of the triple point in the warm sector. I agree with the previous posts that the morning convection should be long gone and any amount of clearing should get CAPE values skyrocketing. Preliminary target would be a Childress, TX to Altus, OK area and head south or east depending on the triple point/dry line position.

I still plan on trying to chase this one. If anyone plans on chasing south central to central OK and wants to meet up to discuss things/caravan PM me. I will most likely need to drive separately so I can shoot up 44 back home after dark to get back to work.

 

[Jim Bishop]

From a large scale standpoint the WRF, GFS and ECMWF are in good agreement. The GFS is the weakest with the surface low over Western North Texas and probably the least optimistic about tomorrow.

Should the WRF scenario verify (which is quite possible) I would expect a a good tornado day over Western North Texas and Southwest Oklahoma. Depending on how the 12z models look I may need to take tomorrow off work (and miss a local energy weather conference too ).

Gabe: I see what you mean about the first wave leaving the region early in the day to mid day, veering the 850mb winds and capping the region. That actually may be a good thing and help to keep warm air advection crap from developing in the afternoon (I think that's what you were implying). The upper lift from the vort max showing up late in the afternoon/early in the evening will be plenty to fire convection shortly after the low and 850mb winds back and increase shear out the wazoo.

 

[Jim Bishop]

Surprised nobody else has posted. But the latest WRF and GFS are not as impressive. They show a more veered 850mb flow and not a well defined surface low. So from these runs it looks like supercells will still fire along the dryline, but the shear won't be quite as impressive, suggesting the tornado threat won't be as high as previously thought.

The 00z runs tonight should reveal whether this pessimistic trend is valid or not.

 

[James Aydelott]

Jim,

that's a great observation, but the low level wind fields tomorrow may play a bigger role, with the 850 veering. Tomorrow could be the classic dry line intersecting an e/w baroclinic zone day. Tonight's convection will play a critical role in tomorrow's initiation and low level wind field.

 

[Bill Tabor]

Eh crapola. I don't like what I'm seeing on current 12z NAM near as much as what I was seeing on yesterday's 12z run. It is much more spread out and less compact now. Timing is a bit out of synch as well.

In particular now I don't see any very strong sfc winds during the day. 850mb's are slightly veered and perhaps not that strong. Early convection may screw things up a bit as well spreading out the convective threat. Additionally the mid level area of PVA is now less compact and is impacting further north and earlier.

So, for now I am taking back my target, etc. It may still end up being a decent starting point, but I will have to reevaluate and study the later model runs.

 

[Jim Bishop]

Jim,

that's a great observation, but the low level wind fields tomorrow may play a bigger role, with the 850 veering. Tomorrow could be the classic dry line intersecting an e/w baroclinic zone day. Tonight's convection will play a critical role in tomorrow's initiation and low level wind field.

True there may be some interesting mesoscale interactions that could back the surface winds and increase the tornado potential. But on a larger scale the veered 850mb flow and weaker suface low/lack of backed low level flow across western north texas decreases the tornado potential.

There will probably be supercells with tornado potential, I'm just saying it no longer looks like a larger scale outbreak like it did on the last two model runs. We'll see what the models do with that trough tonight after we get some hard upper air data into it from California.

 

[Mikey Gribble]

I'm not impressed with the tornado potential. I got suckered into chasing veering 850mb winds on Monday and it isn't going to happen again. I would actually put the best shot of a tornado in southern Missouri (where the moderate risk doesn't even cover). Maybe they could get one or two weak tornadoes in that area, but I wouldn't bet on it. I don't expect any tornadoes over Oklahoma and Texas either, but if they do get a few they should be weak, so I'll be sitting this one out. Just my two cents. I posted a forecast here...
http://loadedgunchasing.com/blog.html

 

[John Cameron]

lets hope the Thu 00z run puts the wind back in our sails. The Wed 12z run backed off the instability, helicity and the location of the dryline. I'm hoping there will be a handful of conditional surface sweet spots. Right now its looks like that would be somewhere between Lawton and Dallas. Here's to a shining sun and a breaking cap!