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

[Jonathan Whitehead]

Well I took a look at the 12Z runs early this afternoon and now have taken a loot at 18Z runs and WOW has the GFS done an about face. What around midday looked like a southward mvmt of the MOD risk now has gone to an expansion of the current MOD risk (depending on which model you believe). The biggest difference is in dewpoint. The NAM is still being consistent in barely bringing 60+ dews west of 35 in OK at 18Z Thr. While the GFS brings 60+dews from SPS to Weatherford to Enid line at 18Z. Thats a significant difference in terms of location of initiation. Both models agree however in track and placement of surface low--S. Central KS.
Overall Im inclined to go with the NAM based on how its handled last couple of events, however, I am aware of the shortcomings behind the NAM so really going to have to wait and see the 00Z runs later tonight to see if NAM comes in line with GFS or GFS continues to be the outlier. This is huge for me in terms of do I go home to DFW tonight and chase front porch of metroplex or do I stay here at OUN and chase W and SW OK? If I have to Ill drive home early in the morning but really wont know prob till I see the 06Z runs and 8am SWODY1. Its only 3 hour drive.

FWIW the GFS has 60+dews all the way up to SJT-MWL-Paris, TX line at 00Z tonight (right now) and um thats not happening per latest sfc obs.

 

[Scott Weberpal]

Given the proximity to home (and downhill trend of the original target), the MO bootheel region looks like a sleeper target for tomorrow. I can't turn my back on the forecasted weak inverted sfc trof sprawled across C. MO by 00z, and attendant backed sfc flow and deep moisture return to the region. Unfortunatly H85 flow is strong veered, but this may potentially be mitigated by nearly westerly flow at H5. Biggest problem may be upstream convection killing insolation. IF (and that's a BIG if) heating can occur, I would expect a tornado report or two in S/SE MO tomorrow.

 

[John Cameron]

I just can't imagine the NAM being consistently wrong about the veering winds this close to the event. GAH! The GFS looks better, but winds are not clearly backing

 

[Bill Schintler]

Chase Target for Thursday, April 3

Chase target:
Milo, OK (15 miles northwest of Ardmore).

Timing and storm mode:
Supercell storms should form along an advancing dryline by 3 PM CDT. All forms of severe weather, including a few tornadoes, are possible.

Synopsis:
Looking at the big picture, a baroclinic leaf is developing over SERN NM/WRN TX while an upstream cutoff H5 low is moving E towards SRN CA. Energy associated with a 130kt H3 streak will surge E through AZ and NM over the next 18 hours as the H5 trough amplifies and moves through TX. A pool of cold (< -20C) H5 temperatures now over AZ will spread NE along with nearly dry-adiabatic lapse rates as noted on TUS, FGZ, EPZ, and ABQ 00Z soundings. LLVL moisture has dramatically increased in the Red River valley over the last 12 hours, with a 200mb deep mixed-layer indicated by OUN and FWD soundings. Meanwhile, 60F SFC dewpoints have spread N to the I-20 area in NERN TX. An elevated MCS developed earlier over OK in response to both isentropic up glide along 300-310K SFCS and lift provided by a S/WV. This convection has exited ERN OK while additional elevated convection should develop over OK, mainly N of I-40, at the nose of a 40kt LLJ during the overnight hours.

Discussion:
This event will be characterized by strong synoptic scale forcing as a 110kt H3 streak ejects from the base of the trough. SFC low pressure initially in the NRN TX panhandle will redevelop over the Hill Country region of TX by late afternoon. During the morning hours, an elevated MCS associated with WAA will be exiting NERN OK. Renewed convection will initially fire along the CF in NWRN OK by the early afternoon hours. Further S, capping will remain strong until late afternoon as the stronger synoptic forcing and cooler temperatures aloft overspread the area and the DL begins to mix E. Convection will initiate from N to S along the DL by late afternoon, and window of opportunity will exist for discrete convection along the DL. The SWD extent of development along the DL will likely be limited by inhibited insolation beneath the CI shield/baroclinic leaf S of the Red River until the evening when the CF dives into the area. By late afternoon through the early evening hours, the CF will overtake the DL from N to S while undercutting SFC-based storms.

Instability and shear should be sufficient for all forms of severe WX, especially with storms along the DL. Steep mid-level lapse rates AOA 8C/km along with SFC dewpoints AOA 65F during the afternoon contribute to MLCAPEs in excess of 3000J/kg along the Red River. Deep layer shear (SFC-6km) will likely exceed 65kts as the aforementioned streak overspreads the area, while hodograph curvatures increase late in the period as the LLJ strengthens. A strengthening LLJ and advancing CF will aid in the maintenance of a large convective area that will travel E through NERN TX and OK during the overnight hours.

- bill
9:50 PM CDT, 04/02/08

 

[Jeff Snyder]

Color me somewhat unimpressed. The setup looked fantastic yesterday, but subsequent model runs are showing an environment much less favorable for tornadoes across OK, TX, and adjacent areas. It looks like a lead wave will be strong enough to significantly veer the low-level flow until mid-late afternoon. The only 00z NAM output I have from WxCaster.com is the low-reso stuff (80km grid), but it's showing abysmal 0-3km SRH at 00z, the result of relatively weak and unbacked low-level flow (5-20kt SW or SSW flow at 850mb ahead of the dryline in northcentral TX and southcentral OK) I really do not like exiting waves in a positively-tilted trough with a cold front poised to crash southward, which is what I'm seeing based on this morning's NWP and the 00z NAM.

Now, that isn't to say that I don't think supercells are in the offing. With 50-65 kt 0-6km shear and 2000-3500 j/kg CAPE, supercells seem to be a pretty good bet ahead of the dryline in southern OK and on southward, and there will likely be some very large hail reports. The 12z NAM forecast soundings showed quite a bit of drying immediately above the surface in the warm sector ahead of the dryline between 21z and 00z, which is likely the result of dry air working in on SSW-SW 900-850mb winds. The cold front is also looking like it will move rapidly southward during the afternoon as the lead shortwave trough pushes into the mid-Mississippi River valley. This normally isn't good when it comes to avoiding undercutting of storms by cold fronts, and recent events have seen cold fronts move quite a bit farther south / faster than models indicated (see March 14th in northern TX for a recent example; 30 Mar / last Sunday / was similar in that the front and a pre-frontal wind shift plunged farther south than models forecast, which pushed the threat area southward accordingly).

Finally, surface dewpoints should be pretty good. However, 00z soundings along the TX Gulf coast don't should a terribly deep moist layer, with ~50mb deep rich moisture at LCH, CRP, and BRO (though better at DRT). Perhaps this is why the 12z NAM forecast soundings showed some drying immediately above the sfc in the afternoon... Regardless, that lead wave looks like it'll be a certain detriment to the chasing prospects for those who were looking at the OK/TX target. I would usually suggest aiming for the apex of any dryline bulge, since sfc flow tends to veer south of such a feature. However, with the cold front sagging southward like the NAM suggests it will tomorrow afternoon and evening, I'm worried about surface-based convection in southern OK being undercut, dependent entirely upon how quickly the front moves (and whether or not the models end up underforecasting its movement).

I'll probably still head down towards the Red River valley area S of LAW, but I'm no longer expecting much in the way of tornado action. We may see problems with updrafts being undercut by their own downdrafts if we end up seeing weak low-level shear and a relatively shallow moisture layer...

EDIT: Dan Dawson pointed this out to me, but the supercell potential could be quite significant based on, for example, the 00z GLE sounding --> http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=024&STATIONID=KGLE ... That near-sfc increase in Td is a bit suspicious, and the near saturation around 850mb looks a tad like shallow convection parameterization. Regardless, >3000 j/kg CAPE and 65kt 0-6km shear in early April is mighty impressive. I'm not sure we'll see the 4700 j/kg SBCAPE shown on that sounding, though. The hodograph is long but somewhat messy, so we'll see (and quite linear up at ADM).

 

[Kevin Crawmer]

I agree that the best chance of supercells is INVOF the Red River. I would choose an Ardmore to Wichita Falls area. One couldn't be wrong there. I think that storms will interact with isolated pockets of CAPE that will get some things going.

I am really intrigued by what the NAM is showing for southern MO like Scott Weberpal brought up. The GFS doesn't give this area much love, but the NAM has it going gang busters with a Sig Tor of 7.0 to 9.0, elevated Craven, Supercell Composite in the 40s, 2000+ CAPE, and elevated Sig Hail Parameters. LSX is leaning towards the GFS with this system, so that would make these numbers a moot point if that holds true, but I think if the dews get up to an adequate level that there would be some leftover boundaries to interact and spin stuff up. Definitely a sleeper spot tomorrow.

Wichita Falls would be a great spot tomorrow. Someone in central/SE OK is going to see something, and West Plains, MO may not be a bad spot to be tomorrow afternoon (bad terrain though).

 

[Tony Laubach]

The GooFuS has given some hope in its 0z run. Wishcasters, including us in our award-winning hotel room here in Lawton (see blog) are definitely pulling some hope out of the GooFuS. It has better surface convergence, surface winds, and an overall better hope for tomorrow along the Red River. Will see how things play out in the end, but at least there is some hope in the spaghetti noodles this evening.

 

[Dan Dawson]

Overall, I'm still fairly optimistic about a decent chase day tomorrow. I don't expect a high-end tornado event, but I do expect at the very least some nice supercells. My target at this time would be the Red River Valley near GLE, possibly hedging a bit further south.

I note how the 0Z GFS is more bullish with the "recovery" of the low-level wind fields after the departure of the lead wave than the 0Z NAM. Also, a quick perusal of the 21 Z SREF suggests that there is some decent uncertainty regarding the amplitude of the lead shortwave, the strength of the low-level winds, and the position of the cold front, to name a few. I completely agree, significant severe looks likely, but it will come down to the short range to really flesh out the details. These types of systems, where you have two interacting streams, and/or a leading wave followed by the main wave axis well separated in time, seem to be particularly unpredictable, at least in regards to severe potential. I recall a few similar systems in recent years, and the details of even the large-scale low-level flow response didn't resolve themselves until the day of the event.

The 0Z EMC 4 km WRF is out, and shows a nice storm just south of the Red River by 0Z, with another group of storms further south in central TX:

 

[Jonathan Whitehead]

Alex and Dan, I think you both nailed it on the head. Whats going to happen I think will be a blend of the NAM & GFS. There will def be enough forcing combined with weak enough cap to initiate daytime supercells along the dryline. With the stronger cap into N TX. I actually wouldnt at all be surprised to see some isolated sig tornadoes west of 35 in N TX. Call me bullish but even though 850 winds are rather meager and somwhat veered, Ive seen enough of this events to know how mod to high instability can overcome that to some extent s/t supercell can create their own environment. I also completely agree with Alex's notion of splitting storms. Def look for that, esp along Red River. I think your def going to get some mommas up to 60 grand.
Im targeting Granbury, TX b/c well...1) I live down there so I can crash (2) cap will be somewhat stronger down there and I believe better chances of tornadoes and mod tornadoes will exist down there and (3) theres the whole metroplex thing.

Well good luck to all.


OH almost forgot to mention the dryline bulge depicted by 00Z NAM in western N TX. Its a looker.

 

[Brandon Lawson]

While hardly indicative of whether or not the main wave will be stronger than progged, I do like how the latest RUC run has shifted the best cape further west by 18z, which agrees with what the 00z GFS is showing.

 

[Ilya Neyman]

Very briefly as it is getting late, but just wanted to point out some things that have caught my eye on the 00z data.

First of all, while the 850 flow has a bit of a gradient from SE to NW, 25-35kt SSW flow up to the Red River by 00z is not bad. Secondly, southerly sfc flow stacks up quite well when you have westerly storm motions per storm relative inflow. 3rd, as everybody's realizing fcsted cape values continue to climb underneath a strong cap, that both the nam and gfs forecast to break through by late afternoon/early evening.

However, the real reason I wanted to write this up tonight is the 850 RH progs. Normally, when you have veered 850 winds in this part of the country that means significant drying. However, on both the nam and gfs 00z runs a batch of nearly saturated air at 850mb moves inland across the Rio Grande, up through W. TX, and then over the Red River, via the scenic route. It's most impressive on the gfs, but even the nam has the 70% RH west of I-35 by 00z. This is significant as not only would this help with cap concerns, but dry air entrainment and moisture depth/quality issues are adressed too.

Now, its wait and see till 12z but right now my preliminary target would be the Red River, + or - 50 miles with initiation possible near or west of Wichita Falls in the 4-6 pm timeframe.

 

[Paul Knightley]

Getting my eye in, ready for the May chase vacation.

The low-level shear is not in the best location during the day, but increases overnight, so we could be looking at some nocturnal tornado activity across N Texas, and perhap Oklahoma. My initial target area remains around the Wichita Falls region - ECMWF is less progressive than the NAM, and looks to be in reasonable shape at the moment. However, although some tornadoes are possible with the afternoon activity in SW/S OK and NW/N TX, as I said above, the late evening may provide the better chance.

 

[Mark Farnik]

After a 9 hour drive from Colorado yesterday and a 12:45 a.m. arrival, meyself, Ryan and Skinner have woken up in Elk City somewhat well rested and scratching our heads as to exactly what we're looking at and where we need to go for this afternoon. Its slightly discouraging to see the strongest low level shear being displaced so far into the trees, at least as far as significant tornadic potential in decent chasing terrain goes. Our initial thinking is to target Lawton and further refine our target south and east as necessary. Initiation looks to be in the 4-6 p.m. timeframe, in the Wichita Falls/Decatur,TX area, if the RUC and WRF hold true.
More later.

 

[Derek Weston]

Top concern after just looking over the setup on the latest RUC would be upper level winds. The best ones are off to the east a decent bit from the best CAPE. NE Texas into Arkansas seems to have the best compromise of the two. (Arkansas after dark perhaps getting more action)

 

[Jim Bishop]

Amazing how this setup has gone from looking really good to less than ideal. The Midland and DFW soundings show a very warm 850/800mb layer. Veering low and mid level winds don't boad well for tornado potential. The best hope chasers have today is the 12z WRF verifying, showing the second shortwave reaching Western North Texas by 00z, and showing a 998 surface low near the Lubbock to Childress region - firing convection across western north texas.

The RUC fires convection pretty early in the afernoon across north Texas which seems completely wrong given the subsidence behind the lead shortwave and the strong cap. I don't see the cap breaking until after 4pm.

I'd expect there will be supercells producing moster hail early this evening. I'm not very optimistic about the tornado threat. Sitting this one out.