2012-03-18 FCST: TX/OK/KS/NE

[Kelly Sugden]

For the high plains, you don't always need completely veering winds. March 28 2007 was largely meridional. That day also had to do with timing. Something tomorrow looks of concern.

http://www.spc.noaa.gov/climo/reports/070328_rpts.html

 

[Jason Persoff]

It's good to use historical precedent to help guide things, but 3/28/07 probably isn't a good analogy. The meridional winds were concomitantly divergent and low-level hodographs did have >90 degrees of rotational shear in areas where tornadoes tracked. Relative to winds aloft, strong surface backing occurred in response to dual sfc low pressure systems (in NE CO and to a lesser extent SE CO). I don't see much backing along the cold front/dryline tomorrow. That may not keep me from chasing, though .

I'm usually pretty cruddy at remembering analogous weather situations despite chasing for a long time. So, I'll pose to the group, what storm date would be considered analogous?

For the high plains, you don't always need completely veering winds. March 28 2007 was largely meridional. That day also had to do with timing. Something tomorrow looks of concern.

http://www.spc.noaa.gov/climo/reports/070328_rpts.html

 

[Kelly Sugden]

I thinking 3/28/2007 except for timing differences Btw, I am not saying tomorrow will be like 3/28/2007. I'm just saying meridional flow is not the end of the story for the high plains. Makes sense.... Too much veer winds create momentum and push the moisture (dl) east. Then again, veered winds across the southeast United States bring wedges. Veered winds relative to what area you're looking at is criterial. Also, history is important as weather events and historical events tend to repeat themselves.

 

[Brett Roberts]

The 00z soundings from south TX this evening looked very encouraging regarding moisture quality and depth, and the 00z NAM solution appears to have reaped the rewards. Several of my biggest concerns with this setup are looking less and less detrimental: if you believe the NAM, LCLs are now down into the 750-1250 m range over most of the eastern Panhandles and adjacent SW KS by late afternoon and early evening. Furthermore, there's a clear trend toward more backing of near-surface flow as the surface cyclone strengthens, and therefore increased helicity prior to 00z. There's not much to complain about, other than the slightly-unconventional hodographs above 4-5 km (owing to a very slight backing with height between 500-250 mb). In my opinion, this event looks likely to achieve something closer to the high end of the potential that has been discussed in recent days. Though the synoptic setup is a bit different than 28 March 2007, the environment over the Panhandles does not look all *that* different (perhaps a tad less favorable thermodynamically, but that remains to be seen with a favorable trend ongoing). If storms can stay discrete for a couple hours after sunset, forecast soundings indicate serious problems for the eastern Panhandles and far western OK.

 

[Kelly Sugden]

I did notice the backed winds in the ul 500-200 hPa... Hopefully won't turn too HPish if that pans out.

 

[Jeff Snyder]

Opening disclaimer: I'm only looking at the OK/TX panhandle target since it's extremely likely that I will be bound to that area.

I haven't had time to examine the 00z runs much yet, but what little I did look at from the 00z NAM is an improvement from previous runs. The SFC-4 km AGL hodographs / wind profiles are extremely nice, IMO. From example, here is a link to a fcst sounding near I40 in the eastern TX Panhandle valid 00z tomorrow evening -> http://bit.ly/FP6Q2c . That hodograph is very long below ~4 km, with some backing with height observed above that height, as has been pointed out by previous posters. That height should be well above the effective inflow depth of the updrafts, but the change in the rotation of the shear vector from rotating clockwise to rotating counterclockwise will affect supercell propagation (via the linear term of the vertical perturbation pressure gradient equation). Any deviation in the storm motion vector that's more to the right of the mean flow will significant increase SRH in this regime.

The primary issue I see remains the dislocation between the best shear (to the west) and the best moisture / instability (to the east). The NAM is showing the best low-level hodos in the eastern TX PH by tomorrow afternoon/evening, in areas with suboptimal low-level moisture. The better low-level moisture (with lower LCLs, higher 0-3km CAPE, etc.) are located in western OK, however. Very rapid moisture advection to the west does help destabilize the E TX pahandle by 03 UTC, but the very strong low-level wind max (e.g. 50 kts at 850 mb from the SSE beneath 40 kts from the SW @ 700 mb) creates a much-hated S-shaped hodograph. Despite the shape of the hodograph, though, the low-level SRH is significant. If there are discrete supercells near and after 00 UTC in the eastern TX PH, I wouldn't be surprised to see a siggy tor out there. This is a big change for me, since I had been very reserved with the setup.

 

[Kelly Sugden]

Backing of the UL winds can also change the hydrometer redistribution back into the updraft... hp's. Happened 4/26/2009 (high risk day) particularly across the ddc cwfa.

 

[Bill Hark]

I think there is a definite chance of photogenictornadoes for Sunday, March 18[SUP]th[/SUP]. There is a trough approaching from the westand 50-60 kt 500mb southwesterly winds are expected to overspread the TexasPanhandle by evening. I really like the southerly 850 mb winds along the eastside of the Panhandle by 18 Z per the NAM that change to slightly southeasterlyby 00Z. The GFS sticks with more southwesterly winds through 18Z, changing to thesouth by 00Z and strengthening overnight. There should be southeasterly surfacewinds from central Texas north along the eastern side of the Panhandle toKansas per the NAM and GFS. I like the predicted 60 degree dewpoints ahead ofthe dryline with CAPE to 1500 in southwestern Oklahoma into Texas and SRHmaxing at 300 along the OK/TX border along the Panhandle. My biggest concern isprecip starting too early in the target area though the NCEP 4.0 km WRF doesn’tshow precip breaking out in the target area until well after dark; differentthan other model precip forecasts. At present, my target is Wellington, Texas.I like the slightly higher forecast instability in this location over pointsfarther north. There are also decent roads leading out in all cardinaldirections. Disclaimer: I am sitting at home in Virginia and am not riskinghours of driving and gallons of expensive gas on this forecast. Good luck tothose out Sunday.

Bill Hark

 

[Dan Robinson]

I agree with Bill's assessment of this event. Initiation time may be the wild card - 00z NAM/WRF and 06z RUC are in agreement about 700mb temps at or above 5C, holding off storms until dark. That's starting to impinge on that general threshold for March outlined by Jon Davies. The 4km WRF (as Bill mentioned) and the RUC do not fire convection before sunset, which is concerning - while the NAM and GFS do pull the trigger on daylight storms. With all guidance showing >40-50kt 500mb winds overspreading the dryline, I would tend to side with the NAM and GFS saying the cap will erode in time.

Definitely a setup I'd chase if I lived closer, being an early season event less likely to be as swarmed with hordes. But even with the next 2 days off, $4/gallon gas is the killer and I will be sitting this out.

EDIT: I would want to be in Shamrock by noon today if I was chasing.

 

[Chip Redmond]

Thanks to classes Monday, we have devoted to chasing the northern target of NE. After numerous model runs cutting off any initiation in that region, we have called off any chase to save money for later dates. Then the 00z models come out...GFS surprised me by calling for cells to fire at 0z Monday. Hodographs are quite indictive of low level helicity in the streamwise direction, however, upper level winds still lead me to believe that storms will not be able to tilt with height and seperate their downdrafts from updrafts, aka be more air mass type storms. Winds post dryline are still southerly an this far north, will greatly reduce dryline convergence. NAM buys this rendition, keeping initiation from occuring. Its an early season bet, but if we had the time to venture into KS, where initiation and convergence are better, without having to worry about being to class on Monday, would definitely head out. Like the OK panhandle and KS border at the moment and would expect best tornadic chance there if early afternoon convective left over cirrus can clear the area. Good luck to all out there!

Chip

 

[Mike Johnston]

Despite all of the conditionals well-covered in this forecast thread, the potential of this setup seems to be holding up fairly well. I like the area in far southwest Oklahoma, along U.S. Hwy 62 from Altus to Hollis, or basically to the TX panhandle border. RUC has been persistent on the last few runs in breaking out precip around 21-22z in this area, models show the cap eroding in the same general time frame. Also, this area is right along the theta-e axis and just out ahead of a suggested slight dryline bulge. Looks like we could see SB CAPE values up around 3,000 j/kg co-located with supportive low-level helicity. I think we're looking at a slightly better than even chance of a few daylight tornado reports in the southern high plains target area today.

 

[Jeff Snyder]

I'm only looking at the OK/TX area of the target, since that's all we'll have time to reach. At any rate, the high-res models are giving a mixed signal regarding convective mode and coverage. HRRR runs continue to show junk developing soon west and southwest of CDS and moving northeastward into southwestern OK. I fear, however, that this is too soon, and I worry about the effects of the outflow produced by these forecast storms stabilizing a large part of the target area before the shear intensifies in the nearer 00z and beyond. I'd rather initiation hold off until at least 22 UTC, and preferably 23 UTC, to give us more time for the shear to intensify. The 12z EMC 4 km WRF looks more favorable for chasers, whereas the 12z TTU 3 km WRF looks worse.

Current satellite data indicate insolation occurring now in the TX panhandle southward into west Texas. The high sfc temps are observed primarily southwest of Childress/Memphis, and this thermal axis abuts the sfc moisture near US 287 in the SE panhandle. Data from the Lubbock 88D indicates some convective echoes now E of Floydada. Farther north (e.g. north of Shamrock), the better low-level moisture has mixed out a tad, with Tds largely in the 56-60 F range. Current Vici profiler isn't very nice looking, though it's also a bit east of my target area.The plan is to head towards Erik to re-evaluate. If something goes up SW of CDS, we'd rather be a bit farther east than intended than be farther west than intended, given 35-40 kt northeast storm motion. I'm hoping we can hold off initiation long enough to give us potent buoyancy for surface-based parcels when the shear strengthens in several hours.

EDIT: I should note that if CI holds off too long, the incoming thick cirrus may actually result in sfc cooling and reverse the ongoing destabilization that's occurring in areas not currently under the cirrus. Some thicker Cu appear to be bubbling in the north-central TX pahhandle northward into the SW KS, but the low-level moisture isn't terribly good up there. We're continuing to keep an eye to the southwest...

 

[Jason Persoff]

Holy smokes the storm NE of Hollis looks beautiful on radar with nice eagle conformation and velocity couplet at low levels. It looks isolated and I am dying to see what happens.