10/5/08 FCST: KS/OK/TX

[Greg Blumberg]

I've been watching the GFS for the past couple of days and there seems to be a consistent trend towards a cut-off low developing over the KS/OK area. This low seems to be producing a pretty shear setup in the 850 and 500 mb maps. Winds are definitely backing, but the 300 mb map jet needs to produce some faster winds for good upper-level support. CAPE seems to be definitely an issue in the models, however the GFS is developing quite a sharp dryline for fall standards, compared to the standards needed for a spring setup.

[Brandon Ivey]

I agree that this system is worth watching. Sunday, October 5th is what the GFS has progged right now for the plains, although in my experience, the GFS seems to be too fast with systems when your more than 3/4 days out. Time will tell!

If the current run is anywhere close to verifying for Sunday, I like the wind profiles and the low that develops in the Texas Pan. (That will help to back the low level flow over OK/Southern Kansas). Wind shear looks okay. The negatives I see are the quality of moisture return which would render low cape values and higher LCL's. If we can get a good return of gulf moisture, underneath the expected wind shear, then I would say Sunday is a chase day for me! For now, I'll keep watching.

[Dustin Wilcox]

Tonights GFS looks pretty sick, just really lacking in the moisture department. The 12Z EURO is in pretty good agreement with the GFS as well, though I would be a lot more excited if I had more faith in moisture making it in time, but by Sunday the gulf is completely open for business, for that reason I am thinking Monday may hold more potential somewhere across KS/NE. Plenty of time to watch the models once again slowly shatter my dreams...

[Mike Hollingshead]

God why can't we have the dews on Sunday. 12z GFS is nuts for the 5th. Sigh.

The low levels are nuts both the 5th and 6th...925mb winds....

http://www.rap.ucar.edu/weather/model/displayMod.php?var=gfs_925_wnd&hours=hr108hr132

Moisture may be ok by the 6th, but mid-levels really start to back to more southerly and I could see a linear fest ensue quickly that day. It is conceivable though to end up with a decent "dual area" day on the 6th, one north in NE area and one south in OK area, much like October 9, 2001. Sfc low with better backed low levels north helping out, and better veered mid-levels somewhere south along the dryline. Of course the 6th would have to also deal with the left overs from the day before.

Damn the dews! Hell, if it was far enough west, low to mid-50 dews could be interesting in the setup on the 12z GFS. It'd be nice to watch it all slow down, and have that 5th setup as it is now, be on the 6th with the better dews. I could almost see that happen too.

[daniel rupnow]

Those wind fields are pretty tantilizing! I wouldn't write off the juice just yet, as both the 12z NAM and GFS have decent southerly flow starting early Saturday, and 55-60 dews over E KS by Saturday evening. 30+ knot S/SE 925mb flow on Sunday will definately help the cause too. I shall keep my fingers crossed!

[Adam Penney]

Ya, certainly going to keep an eye on this situation. If moisture wasnt an issue I would already be planning a chase day. However with CAPE only progged to be at best around 1,000-1,500 J/Kg, Im not getting too excited yet. It is possible that with such great wind fields it could make up some of the difference, but moisture is a major issue at this point.

[Andrew Stoller]

1,500 J/KG with temps in the low 80s in a highly sheered environment is perfect, but as it seems now, with dews on Sunday barely breaking 40, 1,500 J/KG is a pipe dream.

However, if things slow down like they likely will and we can actually get some 50 degree dewpoints east northeast of wherever the surface low sets up and points southward along the dryline, then we've got something to work with.

[Adam Penney]

However, if things slow down like they likely will and we can actually get some 50 degree dewpoints east northeast of wherever the surface low sets up and points southward along the dryline, then we've got something to work with.[/QUOTE]


Well i certainly understand what you are saying, however, even with "50" degree dewpoints, how many GOOD tornado days have there been with that kind of moisture? I'm sure there are many chasers out there that have had some success with these type of days. I'm just not sure it will be worth it for me to chase what would likely be atleast 750 miles roundtrip with that kind of moisture quality. But hey, if we weren't chasers, and always waited for the "perfect" setup, we would almost always be sitting at home, so we'll see. One cannot argue the dynamics with this system, but still the moisture quality as got to come along way for me to get more interested.

[Chris Wilburn]

Tonights run of the GFS does have a swath of mid to upper 50 dews from western KS down to the eastern TX panhandle. This of course will limit the instability and then you have quality and depth of moisture concerns. I guess upper 50 dews and 1,000 CAPE or so could at least make things halfway interesting. Deep sub 1,000mb surface low in eastern CO by 00z. Speed shear is really nice and directional shear is ok I guess. The surface winds don't really back much but the directional shear is adequate none the less. I think tomorrows run of the NAM will show 00z on the 84 hour forecast so you can at least compare the two by then.

[Dave Holder]

Taking a look at some of the forecast soundings, instability will definitely be an issue with this setup.

I think the biggest issue IMO is the lack of colder upper level temperatures, which struggle to advect southward once the low closes off.

It will be worthwhile to keep an eye on things, as the potential exists for severe weather with such an enhanced wind field.

[Greg Blumberg]

The 12z GFS has some hope for the instability problem. Dewpoints in the 60s seem to be promising, but the real question will be the quality and depth of the moisture. It looks like the moisture might be there just in time. The 850mb winds are being very indecisive as to their backing and veering from Sunday to Monday night. I'm hoping they pick backing. I'm not that happy with the upper level support on the 500mb map and 300mb map. Winds could be veered just a bit more in those levels and be a little faster.

Overall, I'm getting somewhat excited by the possibility with each model run. Let's hope it stays on this positive trend, huh?

[Andrew Stoller]

Moisture is now looking to be less and less of a problem, but the GFS and NAM are just not showing any instability what-so-ever.

[Mike Hollingshead]

http://www.rap.ucar.edu/weather/model/gfs084hr_500_wnd.gif

http://www.rap.ucar.edu/weather/model/eta84hr_500_wnd.gif

Pretty big difference in strength and timing between the 12z NAM and 12z GFS for 84 hrs out. All along(at least for the last while) the gfs has been wanting to push it through too fast and has been slowing down and digging a bit. Hopefully something closer to what the NAM has in mind will unfold. Later and stronger.

http://www.rap.ucar.edu/weather/model/gfs084hr_sfc_mslp.gif

http://www.rap.ucar.edu/weather/model/eta84hr_sfc_mslp.gif

Just a little different. Even if you take 12hrs off the GFS it's still a lot weaker than what the NAM has in mind. Look at that thing in the nw!(looks like a beast on the 850mb winds up there (http://www.rap.ucar.edu/weather/model/eta84hr_850_wnd.gif)) .

Go NAM go.

[Michael O'Keeffe]

Whoa that is a change. The 18z WRF is showing 60F tds in W Kansas on Sunday now with 1200-1500 j/kg of Cape with nice helicities. If that is a continuing trend this could turn out to be a great chase after all. Now lets see if it verifies on the 00z.

[Brandon Ivey]

I agree that moisture is looking better for Sunday. Dewpoints are right around 60 along the Texas coast right now, but the layer of moisture is really shallow until you get down to the Brownsville sounding. I still think upper 50 to lower 60 dewpoints will not be uncommon on Sunday afternoon from SW KS to the TX Panhandle. Southerly winds will become very strong on Saturday and Sunday allowing moisture to rapidly return northward. I like the northern Texas Panhandle right now for a Sunday set-up. Monday is looking like western Oklahoma. I am sure I will be out chasing both days. It will be interesting to see how much the models flop between now and then. I just need another fix before the cold weather sets in! It will be a long wait until spring 2009. :eek:

[Andrew Ryan]

The moisture and instability has greatly increased in the last couple of model runs. But the wind fields are starting to concern me. It looks for the most part the best thermos are overlayed with speed shear only. I hope this changes in future model runs.

But either way, there should be some severe weather and I will be happy with that!

[Michael O'Keeffe]

The latest surface obs are looking good moisture wise with upper 50's tds all over OK with low 50s into Kansas already and with southerly flow for the next two days I think the moisture issue won't be a big deal. We will see but as of now the TX Panhandle could erupt.

[Mike Hollingshead]

Monday officially stinks now in my book(now that the NAM fully sees it and mostly agrees with the GFS). Looks a bit like a classic rainy day. Never see anything good off those country wide stalled fronts directly under the upper low. And also hard to think of many good things off a weakening system(low levels are especially toast by Monday afternoon). My only "hope" I think is hoping for some clearing near the upper low center, but it doesn't even appear to be terribly cold anyway. The 850mb winds right ahead of the mid-level vort max are kind of interesting, but, any sort of clearing may be rather hard to come by there.

I think the best hope is the system behind it for late next week. Looks like that one wants to bring winter on down.

[Andrew Ryan]

I still believe that Sunday can be a solid chase day. With the dramatic increase of moisture today, I have little doubt that 50+ dewpoints will be in place on Sunday.
http://hoot.metr.ou.edu/surface/obs/spl

The NAM without a doubt has a much better scenario than the GFS. The NAM has sets up a pretty good scenario for supercells in the panhandle of TX/OK and into parts of extreme SW KS. The forecast soundings for this area looks to be favorable for supercells around 0z. This could become problematic with the days getting shorter.

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=NAM&
STATIONID=KAMA

My only concern right now is instability is on the low side and cold temperatures are a bit lacking in the upper levels. Hopefully, things will become more clear as we go through the day tomorrow.

[Chris Lott]

I think Sunday looks good mainly for the Texas and Oklahoma panhandles. Models do show moisture making it back up that far, but some forecast soundings I have checked out don't show much as far as CAPE. Wind shear looks good but I think this will start with a few cells blowing up the Texas/Oklahoma panhandles and turning linear as it moves east. Just going out on a limb here, if I were to make a "box" for potential severe in the Texas panhandle right now, I would go from Childress to Dimmitt to Dalhart to Canadian. I think anywhere in that area has a good chance of seeing severe weather on Sunday. I made a goof on my part. I originally had Monday posted and meant Sunday.

[Brett Roberts]

It seems clear that the primary inhibiting factor on the models, at present, is ongoing convection throughout the day Sunday over the area of interest. The 60-65 F dew points progged by the NAM throughout the TX/OK Panhandles seem more than sufficient for moderate instability at first glance, particularly given the mixing ratios that yields at 2000-3000 ft. elevation. But CAPE values are depicted as mainly < 1000 J/kg, because temperatures are held in check by the cloud cover and precipitation. If this situation were to change, the dynamic side of this system looks fairly interesting, with ample speed and directional shear. Given the time of year, it would be quite a shame to see a slam-dunk supercell day on the Caprock - and possible tornado day - go to waste because of a lack of insolation. On the bright side, the ECMWF from earlier today is suggesting another major western U.S. trough could be poised to move into the Plains by next weekend.

[Mike Hollingshead]

The 6th is Monday. Sunday is probably the more deserving of a thread by now though. I keep getting confused on a few posts, lol. I'm like, how is the TX panhandle going to erupt on Monday.

[Chris Nuttall]

MOD NOTE: Since that vast majority of this discussion has shifted to Sunday, I'm going to change the thread title, date, and region to match.

[Angie Norris]

I'm thinking Childress would be somewhere nice to be tomorrow evening. There looks to be a bit of a CAPE spike by 0Z...granted, it's progged at only about 1000J/kg, but this isn't May, and 1000J/kg can be enough in early spring or in the fall to make things interesting. There is a nice theta-E spike as well. The winds are bit too unidirectional for my liking, but speed shear is decent. The major limiting factor to instability will be ongoing cloudiness, and I'm thinking we'll see a MCS develop.

[Bill Schintler]

Chase target: 20 miles south of Childress, TX.

Timing and storm mode:
Elevated convection will be ongoing in the TX panhandle early in the period, and will become increasingly surface-based as it expands towards the east. Storms should reach the target area between 3 and 4 PM CDT. A few supercell storms along with an isolated tornado or two cannot be ruled out for any storms that can become surface or nearly surface based.

Synopsis:
Big changes are taking place in the synoptic pattern. The persistent Hudson Bay upper-level low is finally showing signs of breaking down and moving east. Further west, a trough was digging southeast and becoming increasingly negatively tilted with a 50m, 12 hour H5 height fall bull’s eye centered over the Four Corners region. Between these two features, a shortwave ridge over the Upper-Midwest was inching eastward. Convection has fired in the TX panhandle courtesy of a lead H5 wave and some attendant isentropic up glide along the 310K surface.

Discussion:
Regarding model guidance; the WRF, GFS, UKMET, SREF, and NGM were investigated. The NGM is an outlier and is too progressive with forcing and eastward progression of QPF. Recent model runs are more pessimistic with surface-based instability. During the day, widespread CI over western TX will inhibit insolation over most of western TX and the panhandle.

A cold front of Pacific origin will enter the western TX panhandle during the afternoon, while further east a meso-scale low will organize in the Turkey, TX area. Marginal BL moisture is noted, with SFC dewpoints generally AOB 60 degrees. Lapse rates will be poor as the colder temperatures aloft will lag the trough axis. Limited instability will result, with MLCAPEs between 500 and 1000J/kg beneath modest mid-level lapse rates of 5.5-6 C/km. Low-level flow will locally back in the Red River area, enhancing low-level hodographs and moisture pooling. SFC-3km SRH will locally increase to at least 300m2/s2 as a southerly LLJ strengthens to 50 kts between 00Z and 03Z. Deep-layer shear will increase to 50 kts as an increasingly negatively tilted H5 trough shifts east into the area.

- bill
10:11 PM CDT, 10/04/08