3/29/2006: FCST: Central and Southern Plains

[nickgrillo]

Nice! If both of the days continue to look good (WED / THUR) then I will be leaving DTX by late TUE morning for either NE or KS... I'll make it short:

Both the NAM and GFS show an incredible shear and thermodynamic profile across the moist sector on WED afternoon and evening -- with low-level shear increasing by the late afternoon as the southerly LLJ cranks up to 30-40kts ahead of the dryline across the central plains. The NAM currently progs a corridor of at least 1500j/kg SBCAPE stretching from central NE southward into TX -- supported by insolation and sufficient boundary layer moisture (with weakening CIN through the afternoon, resulting in unstable boundary layer ascent by the late afternoon/evening ahead of the sfc trof/dryline). Both of the models show considerabley backed surface flow, which will result in stronger 0-1 km SRH (150-250m2/s2) as the LLJ cranks up by the evening -- with deep-layer wind shear supportive for supercells (and the potential for a couple isolated tornadoes by the evening as low-level shear increases). All in all, this could be a pretty decent two-day setup, with the best part of of WED being the SLOW average storm motions (!) and the potential for some isolated storms.

 

[mikegeukes]

The big question for Nebraska will be, the impact of a melting snow pack, throughout the week
how much moisture will be added to the lower layers of the atmosphere, and will the skies be
cloudy of this.

http://www.rap.ucar.edu/weather/surface/snowNESDISus.gif Current Snow Cover

Mike

 

[Dustin Wilcox]

I cant speak for Central Nebraska but here in E central Nebraska where we too had 18" of snow the snow pack is quickly dissapearing with most of the fields and open areas beggining to clear up. If temps continue to trend as forecasted I would anticipate that the snow pack be limited to shaded ditches and heavily drifted areas by Wednesday.

 

[Jay McCoy]

I have been watching and holding my breath for a west Oklahoma chase for about a week now. The 2 big issues are

1. Timing... will the energy get there before dark?
2. CAP... the 700mb temps really worry me. if we can get enough forcing along the dryline before it retreats wed evening we may be able to get through the lid and have a few isolated cells go up. Otyherwise it will be late in the night when the main trough sweeps through and we get clusters of storms.


I have already taken off work so Kanani and I will be out there "just in case" as usual.

 

[BrandonWhittington]

This setup is starting to remind me of the March 26 setup 2 years ago. I'm going to treat it as the same. Dryline stalls right on the Texas Panhandle and OKlahoma state line. I do totally agree with Jay on the issue with the cap. I would really like to see the temperatures reach the mid 70s just off the dryline. Also, my next concern will be cloud cover. There might be that chance that clouds hold temperatures down. I really don't think moisture return will be a huge problem on Wed. Dews should reach the 50s and I have seen good action with dews in the 50s. Right now, I'm leaning toward a target around Vici, or Shattuck. Still a little too early to pull the trigger.

 

[Mikey Gribble]

My attention is starting to turn from the dryline in western Oklahoma and the Texas panhandle to the surface low in NW Kansas. I am going to wait for the 00Z runs before I set my preliminary target, but unless moisture is going to be an issue in NW Kansas, I think it might be the better play for tomorrow. Precip. and cloud cover could be a problem ahead of the dryline in western Oklahoma. I don't think we are going to have that problem in NW Kansas. I probably won't know for sure where I'm going until I get to see visible satellite and and how moisture advection is coming along on Wednesday morning, but I think it is definitely a chase day.

 

[BrandonWhittington]

I'm not real sure why no one is really intersted in chasing on Wed. Moisture convergance along the dryline appears to be pretty impressive. If we can get dew points in the low to mid 60s along the dryline, I really feel that we will have a decent shot of rotating storms. My only concern now is the leftover precipitation from tonights activity. Hope is starting to build on this issue as visible satellite shows clearing skies in central New Mexico. My target as of now as shifted back to the east and into the Panhandles. I will stick around here in Booker go from there. Things still might be rather interesting on Wed.

 

[Jeff Snyder]

I'm not real sure why no one is really intersted in chasing on Wed. Moisture convergance along the dryline appears to be pretty impressive. If we can get dew points in the low to mid 60s along the dryline, I really feel that we will have a decent shot of rotating storms. My only concern now is the leftover precipitation from tonights activity. Hope is starting to build on this issue as visible satellite shows clearing skies in central New Mexico. My target as of now as shifted back to the east and into the Panhandles. I will stick around here in Booker go from there. Things still might be rather interesting on Wed.
[/b]

I am very interested in tomorrow. Model runs continue to indicate that very strong low-level shear will develop/persist east of the "dryline" tomorrow (strongest in western OK and western KS), and models do indicate that >60F Tds will make it to I40 tomorrow. Mid-upper level flow won't be too impressive, but enough to support 40-45kts deep-layer shear (on par with many of the 2004 chases LOL). This weak-moderate mid and upper-level flow should also help preclude strong cloud-edge entrainment that is often a concern when instability is low and CAPE profiles are slender. In addition, the NAM reduces CINH to near zero along the dryline tomorrow. With relatively slow storm motions, I'm not concerned about storms outrunning the relatively narrow instability axis. The shear vector should be almost 90degrees / normal to the dryline, so discrete activity should be the preferred mode. With the shear and what-will-hopefully-prove-to-be-"sufficient" CAPE, I do think supercells are likely IF we can get initiation. A shortwave should move through the area during the morning, with subsidence in its wake during the afternoon.

Overall, IF we can get initiation, I think we'll see supercells (perhaps more towards the classic-HP range). The strong low-level shear should increase the probability of low-level mesocyclogenesis, and it will also support stronger vertical perturbation pressure gradients that may lead to significantly stronger updrafts than would otherwise be the case with only 1000-1500 j/kg sbCAPE. I'm preliminarily aiming for Shamrock, but I'm entirely flexible right now since a lot will depend upon low-level moisture and any complications from overnight convection.

I do wonder what effect the convection near CRP and northeast from there (been raining in se TX all day LOL)will have on moisture return overnight and tomorrow. The storms down there were producing a nice, organized outflow boundary that may intercept or at least discourage moisture return for some time.

 

[Justin Walker]

I do wonder what effect the convection near CRP and northeast from there (been raining in se TX all day LOL)will have on moisture return overnight and tomorrow. The storms down there were producing a nice, organized outflow boundary that may intercept or at least discourage moisture return for some time.
[/b]

Well the 0z NAM i think certainly picked up on this feature. The Td's before were in the low 60's, but now only low-mid 50's. I very surprised it caught this. Given this trend, the question of IF we have initiation has been answered in my head. I don't think we will have anything fire until after dark until the 50knt llj gets cranking. Otherwise...this system looks good!

 

[Jason Boggs]

I'm not too sure the Td will be much more than the mid 50's along the dryline on Wed. CAPE will probably be sufficient with values around 800-1000. I am concerned with leftover cloud cover with the convection that will be ongoing Wed. morning. The cap forecast of 4-5C at 700mb may present a problem if we don't get some clearing. I am very impressed with the forecasted 3km helicity values of around 500 at 06Z Thur. Another thing I like is the screaming 850 winds of around 45-60 kts at around the same time frame. Also, it looks as though the energy may not arrive until way after dark. Therefore, I believe the most likely time for significant storms will be from 03Z to around the 08Z timeframe.

 

[Kevin Polston]

I was higher on this area yesterday than I am after looking at the 00Z NAM. I had really thought areas of western OK looked decent, especially sw OK. Now.....in agreement with Jason and Justin.....I think the better and more likely scenario is for stuff to get going afer dark when the LLJ cranks up. But considering how flaky the models are at times....it will still be worth keeping an eye tomorrow just to monitor trends.

 

[Chad Ringley]

Tonights (00 UTC 29 March) 4.5 km WRF NMM initates widespread nocturnal convection in the TX Panhandle after 04 UTC 30 March 2006:

http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/cent4km/v2/

In addition to the overnight convection, another wave of convection develops after 10 UTC and covers all of W OK, Central KS, and SE NE through the end of the model run.

Good luck to those who do head to the dryline tomorrow for daytime stuff.. may the surface convergence be with you!

 

[Gabe Garfield]

The 12Z RUC offers perhaps a glimmer of hope to this otherwise untantalizing setup. The RUC suggests that morning convection will move to the northeast, leaving subsidence in its wake. As a result, daytime heating should commence along the dryline, and a narrow corridor of instability should develop (800-1200 j/kg). Tds will be a little low (only in the mid-upper 50s) resulting in fairly high LCLs, but the shear will certainly be strong enough to support a supercell mode. RUC actually removes CINH by 21Z and develops convective precipitation in SW OK by 00z. RUC is perhaps not the best model to be using for a convective initiation forecast, but it at least develops a somewhat favorable mesoscale environment for supercells.

In addition, the exiting convection should leave an outflow boundary in its wake, which the Eta has hinted at for a few days now. This boundary will most likely intersect the dryline in SW OK. As usual with OFBs, it will enhance low-level vorticity, keep LCLs relatively low (along and north of it), and provide a focus for convergence. Should significant insolation begin this morning, I think I will probably venture out to western Oklahoma this afternoon.

Gabe

 

[BrandonWhittington]

Hope is starting to increase with every hour, storm wise for this afternoon. Skies have been clear now ever since sun-up. This has allowed temperatures to warm up into the low 60s already at 9:15 am. Southeast winds have continued to bring moisture north and TDs have reached the low to mid 50s, here in the Eastern Texas Panhandle. If we can get temperatures in the mid to upper 70s AHEAD of the dryline, (I don't see any reason why we shouldn't with the absolute clear skies) and TDs close to 60 by this afternoon, CAPE values should reach the 1000-1200 range along the dryline this afternoon. The more moisture we can get here in the Panhandles, the better our chances are. Storms that do ignite, will rapidly become decrete severe supercells. My target is still at my casa here in Booker. gut feeling is that storms might ignite in the Perryton area. Good luck to all that chases this afternoon.

 

[Jeff Snyder]

Kinda a marginal setup... Obs show mid-upper 50 Tds from central TX into southwestern OK, with deeper moisture heading through western TX as seen by the layer of stratus heading this way. SW OK and surrouding areas to the west should either be seeing full sun now or will shortly. However, the advecting stratus from western TX may put a cabosh on that pretty soon. Given the time of year, and the fact that we are dealing with true gulf moisture, I can't help but imagine that insolatoin will be able to mix out that stratus deck later this morning.

As usual, RUC and NAM not in too good agreement. For whatever reason, the NAM does bring >60F tds up to an Altus to Lawton line this afternoon, but I'm calling it's bluff. As I brought up yesterday, it appears as though the outflow from the convection in southeastern TX yestserday afternoon and evening has blocked the return of the real juice. In fact, obs between Houston and CRP still show winds with a northerly component. Oy! But hey, at least there is some real juice off the se TX coast now, with several buoys and obs in extreme southern TX showing 67-70F Tds.

Initiation will be the main question mark today. Well, CAPE won't be impressive either, especially with only 55-59F tds. The large-scale ascent associated with the wave to the west won't really arrive until after dark. This means that we'll have to rely on dryline circulation and convergence to initiate convection today (perhaps in the face of minor midlevel subsidence too). Low-level shear profiles should be just fine, so any surface-based convection could be of the form of a decent supercell. While mid and upperlevel flow won't be strong, the good directional variation still results in NAM-forecast 45kts of 0-6km shear -- certainly w/in the range for supercells. On a happy note, the weak flow aloft will also mean slow storm motions, with Bunkers forecast storm motion of only 20kts across the OK/TX panhandle border area. But, all of this will be for naught if we don't see initiation until after dark (which is about 130z now allowing for ~40 min of 'twilight' / dusk-lighting). The RUC and WRF do initiation convection in far sw OK before 0z, but the NAM does not.

The lower Tds (<60s) with 70-80F temps won't allow for particularly low LCLs, so I guess we should hope for initiation around 4pm to allow for a supercell to develop necessary vert. pert. press. gradients that will allow it to sustain itself as 0-1z approaches and the surface cools a bit (bringing down the LCLs).