10/11/08 FCST: KS/OK/TX

[Michael O'Keeffe]

The 12z WRF is showing a great setup on Saturday in W Kansas into the Panhandles. CAPE looks to approach 2000 j/kg at 21z with about 1200 j/kg at 0z. A nice, sharp dryline looks to be in place as well as great shear. Storms look to stay more discrete than Sunday possbiliy making Saturday the better of the two days. As of right now I like WC/SW Kansas near the TP.

[Skip Talbot]

I agree that Saturday looks like the day. Although the cap is rather stout in the morning, the 12z WRF shows it eroding it enough to initiate storms along the dryline before 0z. Sheer looks great and the modest instability should be enough for supercells Its important that towers start to go up in the afternoon before the cape wanes off during the evening though. Sunday looks like it could be messy with a lot of forcing on the cold front and early convection keeping the instability low.

[Andrew Stoller]

As long as the cold front doesn't blast through and undercut everything, Sat. has good potential for a brief tornadic supercell. From the afternoon Dodge City AFD:

THE THING THAT IS OF MOST CONCERN IS NEAR-SURFACE
WIND SHEAR (http://www.crh.noaa.gov/glossary.php?word=SHEAR) DURING THE DAY SATURDAY...AS ANY SURFACE BASED STORMS
IN THIS ENVIRONMENT FAR ENOUGH SOUTH OF THE FRONT (http://www.crh.noaa.gov/glossary.php?word=FRONT)...WITH ACCESS TO
PERHAPS 59-62F DEWPOINTS...WILL HAVE THE PROPENSITY TO ROTATE IN
THE LOW LEVELS. SEVERE WEATHER WILL BE A THREAT SATURDAY WITH
ISOLATED (http://www.crh.noaa.gov/glossary.php?word=ISOLATED) TORNADOES A POSSIBILITY AS WELL GIVEN THE CLOCKWISE
CURVATURE OF THE 0-2KM HODOGRAPH (http://www.crh.noaa.gov/glossary.php?word=HODOGRAPH).

[Michael O'Keeffe]

I don't think the cold front will be a HUGE problem. Only because it looks as though the cold front at least on the 12z WRF doesn't want to move much if at all during the day Saturday. It isn't until Sunday when it starts plowing through. I agree we could see a few tornadic supercells though.

[Andrew Stoller]

If things hold, the setup seems like the type where it's an extreme wind shear event near and just east of the triple point. Even if CAPE ends up just short of 1,000 J/KG (because of morning cloudiness and slower clearing etc. or slightly less moisture), I don't think CINH or warm mid level temps will be a concern and the wind shear will be extreme enough to pop something good.

[Adam Penney]

Everything looks to be a go right now for a Saturday chase. Im in agreement that Saturday holds much better supercell and subsequent tornadic chances when compared to Sunday. Shear and helicity look excellent in WC/SW KS, along with what might be just enough cape AOA 1500-2000 j/kg. I agree with Michael in reference to the CF situation. It looks to hang back far enough to not be much of an issue. I have class until noon tomorrow(I hate friday classes!) and will get home to check out the 12Z run, then make a final go/no go decision for Saturday. As of this moment, Im planning on heading to Dodge City tomorrow afternoon. Normally I would just wait to leave very early the day of, however if for some reason there is a drastic change in the frontal position, the TX/OK panhandles could be a play as well. I want to be in postition for that possibility. All in all, very excited about the possibility of one last hoorah for the 08' season!

[Verne Carlson]

12z NAM is showing a better setup moving the triple point north closer to the good SRH in w KS. Looks like anywhere from Scott City, KS down to Dalhart, TX could be the play. Have to see if moisture from hurricane Norbert can get entrained in the low level flow and enhance the dewpoints for this setup. Right now I'm thinking of shooting out from home early sat morning at the last possible moment based on where the surface low sets up.

[Andrew Stoller]

Well, the 00z NAM is out - things look essentially the same - an extreme wind shear environment for west central KS. Dewpoints remain in the mid 50s to low 60s. However, CAPE has dropped a bit to 1000 J/KG or less. I'm less worried about that compared to the kinematics of the wind field, which still looks excellent.

Still keeping my fingers crossed!

[Adam Penney]

Well I'm concerned. There is a big difference from 1500-2000 j/kg to >1,000 j/kg. Someone please inform me on how many "decent"(more than one)tornado days there have been with >1000j/kg of CAPE. Wind shear is great, but there needs to be atleast SOME instability or I am not sure what kind of chase day we can have.

[Andrew Stoller]

There have been plenty of significant tornadic supercells spawned in extreme wind sheer environments with weak instability. The only way you can know whether it will produce is to be there!

We still have a few model runs to go - keep your fingers crossed. I'd be much more concerned if dewpoints were lacking, which they aren't (at least for upper 70 to low 80 degree surface temps.).

[Adam Penney]

I completely agree with you andrew. I have always believed that you have to be there to get the experience. Ya you can bust, but sometimes you are rewarded, so you are right. Sometimes you just have to be there. If we all waited for the perfect chase day, we wouldnt be chasing very often. I tell ya though, the wind fields and helicity are through the roof. If we can get atleast 1500 j/kg of CAPE, I would feel so much better about this setup. We shall see what the 12Z runs hold tomorrow morning.

[Brett Roberts]

I've been watching this setup for a couple days now, and I didn't notice any huge drop in instability on tonight's runs. I'm fairly certain neither the NAM nor GFS have ever showed > 2000 J/kg CAPE anywhere in the Plains for Saturday. The GFS has been very paltry all along, and the NAM seems to be holding steady with its depiction of 1000-1500 J/kg over the Panhandles into SW KS, with perhaps a slight decrease on tonight's run.

This will all come down to the timing and extent of early-day convection, it looks like. Given the moisture in place by Saturday afternoon, instability would not be a problem were it not for widespread junk breaking out by 18z. Hopefully some portion of the unstable axis can stay at least partially clear into mid-afternoon, because the hodographs at 00z Sun. are pretty sick, especially in the corridor between AMA and GCK. I'm cursing the tropical system currently in the Pacific poised to approach the area later this weekend, because it probably won't help the cause for getting insolation Saturday afternoon.

[Dick McGowan]

If we can get atleast 1500 j/kg of CAPE, I would feel so much better about this setup. We shall see what the 12Z runs hold tomorrow morning.

You might not need more than 50 j/kg at the lowest 0-3 km. Scott Currens (http://violentplains.com/2006_Chases/20060128.htm) saw a tornado on January 28th, 2006 in Kansas, in which SPC's mesoanalysis showed only 50 j/kg but had strong surface vorticity, steep low-level lapse rates and very cool temps aloft. SBCAPE was non existent and IMO is irrelevant when chasing these setups. Jon Davies (http://www.jondavies.net/) writes excellent case studies of these types of events and now has a blog he posts to (http://www.davieswx.blogspot.com/) which analyzes recent events and I highly recommend reading them!

I haven't looked at Saturday or Sunday to know if it's a similar type of setup...but I'll take shear over instability 95 percent of the time.

Edit: Archived SPC Mesoanalysis for 1/28/2006
0-3 km CAPE 23z (http://i6.photobucket.com/albums/y230/DickTwister/New/23z_03CAPE.jpg)
LL Lapse Rates 21z (http://i6.photobucket.com/albums/y230/DickTwister/New/21zLL_LR.jpg)
MSLP 23z (http://i6.photobucket.com/albums/y230/DickTwister/New/23zMSLP.jpg)

SPC's Archived MesoAnalysis Website (http://www.spc.noaa.gov/exper/ma_archive/)

[Andrew Stoller]

Well, after reading the DDC morning AFD, I'm.........well............pissed. I haven't been paying much attention to temps aloft and they are in fact quite warm, leading to very weak lapse rates for Sat. It looks as if there will be so much forcing aloft with very little instability, which equals a cluster fu.........getaboutit as far as discrete severe storms. The wind field still looks awesome, but the thermodynamic environment may well kill any chances.

[Adam Penney]

12Z NAM is out and has eleminated all CAPE at OZ across western KS. Looks like the chase is off for me. What a let down....

[Andrew Stoller]

12Z NAM is out and has eleminated all CAPE at OZ across western KS. Looks like the chase is off for me. What a let down....

There still may be some hope - LAHX is showing 800 + J/KG at 00z Sun. But the hodograph isn't as pretty as Garden City. :(

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=036&STATIONID=KGCK

What a shame that has to get killed by no instability/cloud cover and crapvection.

[Michael O'Keeffe]

The 12z WRF model shows a significant cap over much of the interest region through 18z Saturday so how is it possible for precipitation to be on the showing up at 18z Saturday as well. I think I will trust the CINH model over the precip model. Even with 800-1000 j/kg, the extreme shear and high elevation of the region we could easily see supercells and tornadoes as well. Almost every chase I have gone on we usually see more CAPE than forecast anyway, so I am still a go for tomorrow. With hodographs and a system like this it could easily be worth it.

[Verne Carlson]

Have to see in the morning how much Norbert's cirrus shield has been pulled into e NM and w TX and how it will start to affect the panhandles.

http://www.nrlmry.navy.mil/sat-bin/display10.cgi?SIZE=full&PHOT=yes&AREA=pacific/eastern/pac_southwest&PROD=vis&TYPE=ssmi&NAV=epac_westcoast&DISPLAY=Latest&ARCHIVE=Latest&CGI=epac_westcoast.cgi&CURRENT=20081010.2030.goes11.vis.x.pac_southwest.x .jpg&MOSAIC_SCALE=15

It will take every minute of daylight insolation to overcome the warm upper levels. I think I'll wait till the morning and then make my decision on go or no go.

Edit: Latest SPC day 2 expands the slight risk area and breathes a little life back into the forecast as well with the 'T' word again!

[Brian Stertz]

I was looking at the 18z MesoEta and it has most of the strongest lift from the NW Texas Panhandle into NE New Mexico and SE Colorado. The better instability looks like it will favor the western sections of the TX Panhandle and Caprock area and possibly even into E.New Mexico. This one looks a bit too risky to bite on and a little disjointed. I've got a football game to watch anyways so no biggie.

[Adam Penney]

Well I have to say, as of right now, I am very glad I decided not to head out the door and chase tomorrow. The new 00Z NAM is out and has dropped dewpoints even a little further. Also the best dynamics along with greater helicity values dont kick until ~0Z, which by that point, most of the instability(whatever little there is) is gone. This still could be a case of high risk/high reward, but I have very little experience with low instability/high shear days, so I will sit this one out and see if I can learn a bit.

Good luck to all that take the chance!

[Shane Adams]

Fall systems need to be sure things a few days out. The problem is always thermodynamics. It's quite easy to get good shear in place, but that alone is worthless. I'd much rather tackle a low-shear setup with amazing instability than watch all my towers getting sheared over and ripped to shreads by an insane speed max with little or no instability to support it (like what will happen tomorrow).

I look back on all the Fall systems I've chased, and all the decent ones I knew I was chasing before the day of.

[Bill Schintler]

Chase target: Andrews, TX (32 miles north of Odessa).

Timing and storm mode:
An extensive area of mainly stratiform precipitation will be ongoing in the TX panhandle and into eastern NM during the early afternoon. This will expand east towards the target area between 3 and 4 PM CDT, while becoming surface-based. A few supercells will be likely east of the main precipitation shield.

Synopsis:
Changes are underway, with an amplifying H5 trough in the western US. Upstream 00Z soundings (MAF, AMA, EPZ, ABQ, FGZ, TUS, and MGYM) all indicate meager low-level moisture and poor lapse rates above 600mb. At the surface, dewpoints have been inching upward over the last 12 hours with southeasterly up sloping flow, and were pushing 60F over much of western TX. The WRF, GFS, and SREF have a good handle on surface moisture.

Discussion:
CI will overspread the TX panhandle from the southwest by late morning, limiting insolation. Instability will be limited, despite surface dewpoints in the low-60’s F with the help of large-scale up sloping flow, owing to modest mid-level lapse rates of 6C/km. The colder upper-level temperatures will remain well west of the area. MLCAPEs will struggle to reach 1000J/kg. Moisture at all levels will increase courtesy of Norbert. An area of SC will develop between a Midland to Lubbock line, and the TX/NM border, by early afternoon as a tongue of 15C-16C H85 dewpoints surges northward.

Both deep-layer and low-level directional shear will be sufficient for storm organization. A southerly LLJ will strengthen between late afternoon and early evening. In response to this, SFC-3km SRH will increase to 200m2/s2 late in the period. A modest tornado potential may exist with LCL’s in the 800 – 1000m AGL range. SPC significant tornado and supercell composite parameters of 0.5-1.0 are indicated.

- bill
11:00 PM CDT, 10/10/08