4/9/08 FCST: TX / OK / KS

[Donald Giuliano]

After reviewing the latest model output, it appears as though Wednesday may finally yield a really good-looking setup for the Southern Plains.

I've been increasingly interested in tomorrow while reviewing the last few model runs, and the 12Z NAM is no exception, despite the fact that I have never seen anything good near Wichita Falls. At least this time around the setup is much more classic than any other time I've been down there, with a nice jet nosing around the base of a beautiful upper-level trough and strong low-level flow ramping up in the warm sector, especially around/after 00Z. Storm motions are also not especially fast as the main upper support is still well off to the west, hopefully making for a nice, leisurely chase. I would still like to see the warm front cruise a little further north than the models are forecasting, but beggars can't be choosers.

After dark things really start looking crazy as the warm front continues to lift north, with the possibility that storms may remain surface-based through the night in Oklahoma. Couple this with a shear profile that borders on the insane by 12Z Thursday morning (esp. in eastern OK), and there's the strong possibility that it could be a very long night.

 

[Jeff Snyder]

There are several things to like about this upcoming chase setup, including moderate CAPE and strong shear. Again, it looks like low-level shear will be sufficient for strong tornadoes tomorrow afternoon and evening, perhaps extending into the overnight hours if the GFS verifies.

My primary concern, however, is one that is common to have this time of year (and one that likely killed yesterday) -- moisture. Models are forecasting the juice to be located southeast of the DFW metroplex tomorrow morning at 7a (1200 UTC). Cyclogenesis back in western TX should allow for winds to veer behind the cold front from a N/NE direction to a SE direction, allowing for the rapid return of low-level moisture closer to the dryline. However, this may turn into a 'just in time' moisture return event for those who are looking at the dryline in western TX. Output from the 15z SREF guidance indicates that the mean position of the 60F isodrosotherm at 12z tomorrow will be from near Texarkana to Sonora. On SE sfc winds, 60F tds will need to move approximately 275-300 miles northwest to hit Aspermont in 12 hours' time, necessitating >20 mph sustained winds. Of course, this does not include any effects of mixing. The current NAM forecast shows 10-20kt southeasterly winds across central and northwestern TX tomorrow, which may or may not allow the 60F isodroso to make it to northwestern TX before sunset. The good news is that the NAM is showing moisture above the sfc taking a bit more of scenic route across southwestern TX as it advects quickly ahead of the dryline on 25-40kt S (in the mean, at least) 850mb flow. However, as we saw yesterday, there may be big problems for daytime supercells if the models end up being too quick to return this moisture (i.e. overforecasting tds = bad). It's worth noting that the GFS is quicker / farther NW with moisture return, thus also leading to higher CAPE (with >1500 j/kg to the Red River by 0z) than what the NAM is forecasting.

A secondary concern that I have pertains to a possible effect of such a rapid moisture return -- early convective (elevated) development. I'm worried that we may see significant / widespread elevated convection forced by strong isentropic lift and theta-e advection from the mid-morning hours through mid-afternoon. The 12z NAM is showing significant QPF between 12-18z tomorrow across much of central and northern TX, which may help impede moisture return and inhibit destabilization until early evening. The NAM is still showing signs of convective initiation along the dryline in western TX by 0z, while the GFS seems to hold off on dryline convection until the 00-06z time frame.

I'm trying to keep my eye on the Throckmorton to Aspermont area, since I'd really rather stay N of I20. I have so much stuff to do, but this looks like the last chase around TX/OK for a couple of weeks since the Gulf gets a complete flushing late this week and through the weekend, and the progressive pattern that we've been in slows down quite a bit. Given this, I'd like to chase.

Initial target is difficult to pin down now given uncertainties regarding mid-day convection and specific location of dryline by afternoon (the NAM appears to be farther W with the dryline, close to LBB by 0z; the GFS is farther E, nearer the longitude of CDS). I guess I'd say somewhere between Throckmorton and Aspermont looks good for this OUN-based chaser. I'll stay home tomorrow if it looks like mid-day elevated crapvection is going to trash the warm sector (at least trash it for pre-00z sfc-based convection).

 

[Jim Bishop]

A secondary concern that I have pertains to a possible effect of such a rapid moisture return -- early convective (elevated) development. I'm worried that we may see significant / widespread elevated convection forced by strong isentropic lift and theta-e advection from the mid-morning hours through mid-afternoon. The 12z NAM is showing significant QPF between 12-18z tomorrow across much of central and northern TX, which may help impede moisture return and inhibit destabilization until early evening. The NAM is still showing signs of convective initiation along the dryline in western TX by 0z, while the GFS seems to hold off on dryline convection until the 00-06z time frame.

I believe your concerns are both real and significant. Both the WRF and GFS develop rain/convection from isentropic lift across western/north texas by 18z with no cap. I think tomorrow is going to be quite the mess during much of the day and any hopes for discrete supercells will wait until the evening or even after dark.

 

[Jonathan Whitehead]

Sorry but I just had to post this

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORMAN OK
1000 PM CDT TUE APR 8 2008

DEVELOPING NEGATIVE-TILT TROF OUT W... WITH UPSTREAM 160-KT JET
MAX DIGGING INTO ITS BACK SIDE... HAS THE POTENTIAL TO SET OFF A
MAJOR SEVERE WEATHER OUTBREAK WED-THU AS IT SWINGS FROM TX TOWARD THE LOWER/MID MS VALLEY. DEPTH AND QUALITY OF LOW LEVEL MOISTURE WILL BE CRUCIAL... ESPECIALLY AS FAR N AND NW AS OUR CWA WHERE THERE IS STILL A LOT OF WORK TO BE DONE IN TERMS OF LL MOISTURE/ INSTABILITY. IF INSTABILITY [and moisture] BECOMES ADEQUATE... THE SYNOPTIC-SCALE SETUP SUGGESTS THAT THIS ONE COULD RIVAL SOME OF THE MORE NOTORIOUS APRIL OUTBREAKS OF THE LAST SEVERAL DECADES. 24

Impressive but im not buying it. From the models and forecast soundings ive seen, this is a quagmire. Basically your dealing with massive atmospheric hemorrhaging above the surface with regards to significant widespread elevated severe crapvection. Youll be lucky to get any sunshine out of this one or any type of discrete supercells. Most likely will have to wait till after 00Z for anything discrete/sfc based along dryline (as Jeff mentioned). I was going to post a link or attachment of 12Z NAM forecast sounding/hodo for FWD but unfortunately I closed the window and calling it up in history only updated with 00Z run but 12Z showed impressive hodo looked like large backward letter S on its side.

I may be wrong with my prediction but im just not liking looks of this.
And warm front will struggle to make it cross the Red River. One thing that is a positive is the backed low level flow similar to Monday (that didnt do s^&t in OK). Will be curious to see how SPC handles this one.

 

[Bill Hark]

Very nice setup for severe weather across central Texas for Wednesday April 9. There is an approaching trough that will give nice upper level support. The 00Z init April 9 WRF shows 40 to 50 SW winds at the 500 mb level overspreading the area by 00Z April 10 while the GFS 00Z init April 9 is similar but with slightly higher speeds of 50 to 60. I don’t think the cap will be a problem except in far SW and S Texas along the 10 degree line at 700 mb. The 850 winds will increase through the evening and overnight hours mainly from the south. According to both GFS and WRF, there will be backed surface winds through most of central Texas. The GFS shows a low over the Odessa area by 00Z moving slowly to the northeast while the WRF shows the low more near the Big Bend area also shifting northeast. 60 to 65 dewpoints will move northward toward the Oklahoma border on both models though they differ on a predicted small dryline punch (GFS north of Big Spring/WRF just SW of San Angelo) SRH is forecast to be 150 to 200 by 00Z with improvement overnight. Like many other chasers, I am very concerned about early and widespread precip as forecast on both models. I see two possible targets: along the dryline and following the warm front. I think there will be somewhat more photogenic and discreet storms farther south along the dryline. As of this evening, my target would be Sterling City. I’ll adjust my target to be just north and east of the predicted dryline punch.

Bill Hark

 

[Bill Schintler]

Chase Target for Wednesday, April 9

Target:
Snyder, TX (70 miles southeast of Lubbock).

Timing and storm mode:
Elevated storms will be ongoing throughout much the day. In the wake of the elevated convection, surface-based storms will develop after 4 PM CDT with supercells producing a full spectrum of severe weather including a few tornadoes.

Synopsis:
ULVL flow indicates an increasingly amplified WRN CONUS trough with 130kt H3 flow diving S towards the PAC NW. On Wednesday, several small-scale pieces of energy will eject from the trough base during the FCST period and provide two primary shots of UVM on as steep mid-level lapse rates currently over NM overspread the area. Elevated convection will fire in response to the lead wave, with strongest UVM exiting the area for OK by noon. Late in the afternoon, a second wave will bring a N/S oriented band of intense UVM to the TX panhandle and SFC-based convection will fire along a DL. Meanwhile, SFC Cyclogenesis will occur over the WRN TX panhandle while increasing return flow of moisture to the area.

Discussion:
This is somewhat of a complicated FCST owing to lack of obvious SFC features as a focus for convection as well as widespread ongoing elevated storms during much of the morning. Additionally, thick ST will blanket the area during much of the period while inhibiting insolation. During the afternoon, an advancing DL and attendant clearing of ST should provide the focus for SFC-based development along the SRN periphery of the ongoing precipitation and cloud shield.

The second of two lead waves will provide lift while deep-layer shear increases to 60 kts. A CI shield moving from NM into WRN TX late in the day will be a visual indication of the arrival of this wave and its attendant lift. Following initiation; shear, moisture, and instability will be ample for all forms of severe WX over a limited area. Large hodographs and directional shear in the SFC-4km layer will result as 40kt SWRLY mid-level flow races over backing LLVL winds. Local enhancement and backing of the SFC flow is also likely in the Caprock Escarpment area. Instability will increase with differential advection of steep mid-level lapse rates and SFC dewpoints of 60-65F, with MLCAPSs increasing to 2000-2500J/kG. Later in the evening, the SFC low will track into OK while sweeping a CF of Pacific origin through the area. Storms will increase during the overnight hours with linear forcing from this feature after it overtakes the DL, with the primary threat transitioning to that of severe wind.

- bill
12:18 AM CDT, 04/09/08

 

[Ilya Neyman]

Several concerns/questions with this upcoming event. First and most obvious one is the amount of moist sector convection, developing in the morning and lasting into the afternoon hours per model agreement, the extent of which will determine instability, frontal positions etc. Second, is cap strength and whether it truly will be able to hold surface based stuff from going up early in the day and far SW across TX. Third is surface based initiation after the early storminess clears out.

It seems that models latch onto a substantial lead impulse that pivots out of the SW and is the catalyst for the morning-early afternoon elevated activity. After this happens, there looks to be a lull in the moist sector, and by 00z, there's not much in the way of convective indications on the models. Temperatures, progged well into the 70s and 80s ivof dryline along with 60 dewpoints and strong theta-e ridging, impressive/uncapped cape all would point to late afternoon-early evening initiation. One possibility is that subsidence in the wake of the morning shortwave may supress things until after 00z when the main system ejects out. This is supported reasonably well by both the gfs and the nam where convection is forecast to fire by 6z.

A second and equally plausible scenario would feature 2 rounds of sfc-based storms, with the first one being in the late afternoon-evening, moving off of the dryline and the second one later at night with the main wave and dynamical forcing.

Either way, once storms form they look to be getting very intense. I too am concerned about a significant nocturnal tornado risk along the warm front from NW TX into OK. The boundary layer should destabilize through the night as rich moisture floods NW and mid-level cooling is met up with upper level diffluence increasing lift and sustaining rising motions. Models have been consistent in their depiction of discrete and possibly supercellular structures traversing the region once initiation ensues and the instability/lift/moisture all look to sustain this activity well into and possibly through the night.

Anybody seriously considering chasing this event, be aware, this could go very long into the night.

It will be interesting to see what SPC comes up with here in a few minutes.

 

[Bill Tabor]

After briefly reviewing I'm a bit more concerned with stronger convection breaking out south of SPC's Mod area in the slightly more capped, but better dew air. Sure the majority of the mid level flow will be affecting the mod area but I think we'll get lift a bit further south as well.

Just as a hunch from watching many of these unfold...I'd say we have substantial elevated convection going on top half of Tx near 12z and into the early day morning with stronger cells on the southern fringe. Perhaps there will be some action down toward DRT as we get some lift from backed winds over the mountains. Pecos area likes to get in on this action too. I suspect that among the many rainers and hailers there will be your scattered tornado warning during the day that a chaser would have to have his scuba suit on to find. Perhaps that action will move off eventually ene with a slight lull and renewed activity more supercellular. Perhaps and MCS will form with embedded sups late.

Guess we'll see. For now I will monitor locally in the morning just to get a clue of how things are looking. I think it is one of those 'wait and see' days and until all hell breaks lose...assuming it ever does we may have to carefully pick our way to find a reasonably likely target.

 

[Todd Rasmuson]

TARGET: TBD
TIME: AFTER 4 PM MOST LIKELY

very complicated situation to say the least as has already been said, Jeff made alot
of great points and this whole situation with overnight convection also has me worried, but time will tell, also a bit concerned with how well overall dewpoint's
will be by later today... my decision is one of stay close to home in the dfw metroplex and hope something blows up just w of here out say mineral wells or head further west then that for a better possibilty, anyone have any suggestions shoot them my way, appears though this is gonna be a last minute decision it seems with just the waiting game to see how long this am stuff is going to last -Todd

 

[Paul Knightley]

Very complex scenario but I would still opt for the Brownwood region as a starting point and then basically take it from there...as far as ECMWF is concerned, by 18Z, 60F dp line goes from Big Spring to Sherman, TX, with 65F dps from SW of Abilene to Paris, NE TX. 21Z, 60F dps from Sweetwater to McAlester, OK. Area of 68F dps around Stephenfield, TX to DFW. 00Z - large area from Abiline to McAlester back down to Tyler, TX above 64F, with 68F around DFW.

 

[Shane Adams]

The RUC is being stingier with the northward movement of the WF, much as it was on Monday...and I'm starting to buy it. Seems the initial activity will do its thing and move on east and north, like it does every time in this typical early-season type of scenario. What's left in its wake will be a combination of elusive boundaries, and possibly an hours-long subsidence lull. Regardless, the area will once again destabilize, and initiation will be likely along the TP/DL areas. Maybe it's just me but this looks an awful lot like Monday, but further south, and with better forcing.

My plan is to drive south to the WF, then follow it west to about 50 miles east of the dryline. With today's expected storm motions/speeds, I want to stay north and east of where I expect the best stuff to form. Also, the deepest moisture seems to want to pool well east of the DL initiation points, so I expect elevated hailers the first hour or so of development....and if the plan works, they will move right into my lap as they tap the better air. Maybe I over-simplify things, but today doesn't seem complicated at all IMO...just messy.

 

[Sam Barricklow]

Target Area

This morning's COD RUC is pointing to the area from Abilene to Weatherford and NNE to Wichita Falls to Gainesville, with an early show starting around noon and continuing through late afternoon. Much will depend on the location and movement of the warm front. If it slows down, then the window of opportunity may be narrower and restricted to areas along I-20.

The lead shortwave is forecast to move into Oklahoma by 21Z, with a training tail of PVA draped across the Metroplex by rush hour. The most intense storms should be just ahead of this upper level feature, above the best low level EHI.

Traffic around the Metroplex is to be avoided! Morning rush "hour" begins at 6 AM and thins out around 9 AM. Afternoon rush "hour" begins around 3 PM and thins out around 6:30 to 7 PM. Don't get caught ahead of a supercell in the DFW traffic quagmire unless you can find somewhere safe to hide. Sitting in traffic for an extended period on one of the interstate highways is almost guaranteed when any rain falls.

Choices for bypassing DFW to the south are limited, with 287 being one of the few choices. To the north, highway 380 is the choice. Trying to drive across DFW on IH-20, IH-30 or a combination of IH-820 to IH-635 are losing choices. The only reason to venture into the rush hour Metromess would be if you were to try to video or photograph a tornado in the act of urban renewal. Note that many areas are now similar to war zones, with high crime rates. In Dallas, the worst areas are generally south of an east/west bisection through the center of town, but other areas can be risky too. I'm not too familiar with Cowtown, but do know that the near east side of downtown should be avoided.

Looks like the strange attractor has a bead on the Throckmorton to Scotland area this year.

 

[Andrew McDonald]

I'm with you on this one Shane. I just posted my thoughts on the Australia Severe Weather Forum....here are some snippets of it...note that I did a forecast for this day 24hrs ago and picked Aspermont as my target (hence the reference to Aspermont below)...

"Ok...time for an update. Haven't yet looked at SPC's outlook but I'm suspecting they may move the risk area further S than initially anticipated. If I was in Aspermont, Tx now I'd be wanting to drive S rather soon. The latest RUC (which extends out to 21z - with 0z being the prime time) shows distinct failure of moisture return up into the texas panhandle tomorrow. That said, it is still quite a complex set up tomorrow (being today for the US guys) even if a few small things change, it could become potent rapidly. It looks like widespread convection will pop up with the strong forcing from the upper trough which is set to dig in and this widespread convection could kill off the chances of an outbreak across northern texas into the south eastern parts of the panhandle. That's why I'm playing the southern option....too little moisture return further N and too greater chance of being cluttered.

My initial thoughts are to play just S of I-20 maybe somewhere around Ballinger (half way between Abiline and San Antonio).

Current analysis shows the warm front holding back a heap of juice with mid 60's DP's ready to boot north eastwards towards the target area over the next 8 hours. If that boundary doesn't move over the next 4 hours, I'd be wanting to boot even further S as that may end up being the play of the day.

So lets say Ballinger for now but like I said, if that warm front hasn't retreated N any by midday, I'd be looking to hit the road and get down nearer to I-10. Maybe Ozona. (bit of a dryline buldge heading for this area...interesting)."

Macca

 

[Jeff Snyder]

Looks as good as I was expecting it to look. 12z RUC has >50kt 850mb flow from between W of Mineral Wells to E of the Metroplex by 0z, with NAM showing 45kts thereabouts too. Given the current lack of widepread convection between I20 and the Red River E of Throckmorton and SPS, it looks like a "go". I'm torn between heading SW on I44 and dropping southwards, or heading S on I35 and W of I20 -- 2nd route should be longer, but may be a tad faster. In addition, I'm worried about being in the cool sector so long if I do I44.

The 15% hatched area looks well-placed in my amateur forecasting opinion, and I like the area 50 mi N to 30 mi S of a the I20 corridor between ABI and DFW.

 

[Tim Marshall]

TARGET: Brownwood-San Angelo, TX TIME OF DEPARTURE: 10 AM. Strong dynamic storm system to strike Texas today. PROS - Large trough in the west with plenty of lift and upper level winds. A warm front is nearly stationary south of a San Angelo - Brady, TX line and should lift slowly toward I-20 later today. There is plenty of moisture in the warm sector with 70 dews. NEGS - Lead wave already has ignited convection across west Texas. Cloud cover has socked in the warm sector and there is little in the way of a dryline progged today to roar eastward before dusk. I fear there will be lots of storms racing north-northeastward in difficult chase territory. Looks like a messy day to me, but I hope to stumble upon a nice storm. I'll head west on I-20 then drop southwest to Coleman and head west to SJT. TM