4/29/10 FCST: TX, OK, KS, NE

[Dean Baron]

Been watching this system for a few runs on the GFS. I like that the GFS is less progressive with the system now, bringing it in to central KS down through central TX by 00z April 30th. Moisture return doesnt look great but it looks like moisture might increase throughout the evening. Waiting for tonight for the setup to get within WRF range before I take too close of a look at it but thought I would start up discussion. SPC has Thurs. highlighted in the 4-8 day outlook. No class for me Thurs/Fri so this is perfect timing.

 

[Mikey Gribble]

4/29/10 FCST: KS,OK,TX,MO,AR

I kind of got caught off guard a little bit with the 00Z run of the GFS for Thursday. The 12Z run had this setup in Iowa and Minnesota and instability was all but nonexistant. The 00Z run from last night shifted the setup much farther south though and it is currently showing the cold front dryline intersection over central Kansas.

I don't want to get into any details now since the NAM picks up on this this today. I am definitely looking forward to the 12Z runs this morning. SPC did highlight this in their 4-8 day outlook. The reason it has my attention is because of the extremely strong wind fields with this setup. The last two runs of the GFS (only ones I paid attention to) have shown exceptional 850mb-500mb crossover. The directional component isn't very good, but the current run of the GFS is showing 50kts at 850mb and around 70kts at 500mb. IMO when you have wind fields that strong if a couple other ingredients can fall in place you can have an extremely potent setup. I am very interested in what this setup will look like later this morning.

 

[Stephen Jones]

The model runs have been pretty inconsistent so far. The Euro model has it slowed down by about a day that it appears to me.

GFS though as of the latest runs (such as the 00z last night) has been showing insane speed shear at 850mb and 500mb. The only problems looks as if it might be in the jungle before convection may even get going. 00z NAM of last night ended at 84hrs of the trough being further west and slow, which may mean a more feasible area to chase in. This is just my two cents!

 

[Darren Wilson]

I too have been watching this setup for some time now.The GFS, which is being very inconsistent with this setup so far, is more progressive than the NAM, which has now picked up on this setup. It will be interesting to see how far east the dryline can mix during the day on Thursday, my guess is somewhere near or just west of the US 183 corridor in Oklahoma. The NAM allows for good surface heating, while the GFS maintains a bit more low clouds but pushes the dryline closer to I 35 with LCLs lower. Both models show a very strong wind field however. Waiting to see the 12Z GFS, hoping it slows down and trends toward the NAM.

 

[Derek Weston]

Latest NAM is relatively similar to what the last few GFS have showed... albeit, a bit further west.

Long, skinny corridor of CAPE from South Dakota through Texas. Doesn't look like anything much will break 1500 j/kg.

Big ugly cold front looks to be forcing things to the north. Further south... a bit more room for the DL to work its magic.

Ample speed shear, as has been noted -- storm motions look to rocket north pretty quickly -- but largely unidirectional. Storm mode certainly in question -- any supercell activity to the north would seem to be of the embedded nature.

Further south... SW Oklahoma area or so ... shear profiles slightly less linear. Perhaps a tail end charlie type play.

Not too impressed.

 

[Scott Weberpal]

I'm with Derek; at this point it looks like a potent squall line/perhaps QLCS type system with perhaps an outside shot at a discreet supercell far south.

Here's hoping we have more backing the low-level winds, or more veering of the mid-tropo winds or it'll be little more than a pretty shelf cloud and strong outflow day.

 

[Skip Talbot]

With a very deep surface low, very strong speed shear, and modest instability, I think this day could definitely be very active with supercells from Nebraska down through Oklahoma. The GFS is slowing down and converging with the NAM's solution, which is probably more realistic. Speed shear and instability more than support supercells down the length of the dryline from southern NE to OK. The hodographs are not the best further north. With more of a straight line hodo we could be seeing a lot of splitting storms and a quick transition to a linear mode. Still, 850 and 500 mb wind crossovers look quite favorable for supercells. I'd expect storms to not be as discrete further north with the excessive forcing from the cold front in Nebraska and the upper level dynamics associate with the jet max in Kansas. The low levels are also largely unidirectional in this area, though, and this could hurt our tornado chances. Into Oklahoma however, the hodographs curve a lot more at the bottom. The better low level directional shear and less excessive forcing could give us our best chances for discrete storms and tornadoes in this area. Right now I'd target the I-35 corridor from Wichita to OKC for likely supercells and a few tornadoes somewhere in the mid to later afternoon when the cap is forecasted to erode.

 

[Mikey Gribble]

Shear vectors are normal enough to the boundary for discrete storms along the dryline. Further north where the cold front has overtaken the dryline and 500mb winds are backing more I think you will see more of a broken linear type convection.

I agree that the Wichita to OKC area looks best. I like the southern potion of that area best where you get a little better directional component in the 850-500 crossover.
NAM has SBCAPE >1500J/kg ahead of the dryline in a north south line from Wichita to OKC. Dewpoints are forecast to reach 60 in the I40 area.

I hate being overly optimistic because we all know how setups can totally crap the bed this time of year, but any time you get backed 850mb winds approaching 50kts during daylight hours, that's pretty damn impressive. The 850/500 crossover in Oklahoma is just nasty. If you can really get >1500J/kg and dewpoints of 60 degrees, that is certainly strong tornado material IMO. You can't ignore wind speeds that strong in the low levels. That is pretty much the one thing most strong tornado environments have in common.
I need to spend some more time looking over data and I really want to see a forecast sounding and hodograph, but from what I've seen so far I would feel very confident in a tornado outbreak occuring if the NAM verifies.

edit - here is a link to the GFS sounding and hodograph for OKC. There is a stout cap that erodes from 18-00Z that might be of some concern. The hodograph is very impressive IMO.
http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=GFS&STATIONID=KOUN

 

[ericjkelly]

I am too watching the Centrals plans on Thursday...Just not sure how things will line up. Looks like enough moisture and the Shear looks good...

I will wait and watch!

 

[Jeff Snyder]

I won't spent much time on this now since the forecast will change by Thursday anyway, but I do have plenty of concerns. My greatest concern right now is moisture quality... How wide will the >60F Td corridor along the dryline be? If temps hit the 75-80F range, will a 15-20F dewpoint deficit be too large for a substantial tornado risk?

The forecast hodographs look pretty good (and great, on the GFS in western Oklahoma) just ahead of the dryline, but the strong flow aloft also means that forecast storm motions are fast -- 40-45 kts in Oklahoma increasing to 50-55 kts in northern KS and NE. The timing of the vort max aloft looks good on the NAM and GFS for afternoon initiation, and I hope to see the ECMWF's forecast of a sfc low in far southwestern KS instead of an elongated low like the NAM and GFS are showing.

Again, not worth putting too much time into this one until we can better ascertain the moisture quality (and width of the higher-quality moisture) since I think low-level moisture may be the limiting reagent in this mixture of atmospheric goodness. I wouldn't mind if mid/upper level flow weakened a bit to help bring out storm motions into a more favorable regime (<35 kts, but that slow is unlikely). As Mikey noted, whenever we see a forecast of 45-55 kts at 850 mb near and not too far ahead of the dryline at 18z and 00z this time of year, chasers should pay attention.

 

[Brett Roberts]

This has the look of a classic early-season or autumn low CAPE/high shear setup, which is tough to get excited about in the central part of the Plains, where such a combination rarely works well. Hopefully subsequent model runs will improve the low-level moisture and we can at least see some solid 63-65 F dew points ahead of the dryline/cold front. (Thankfully, one of the few good things I've noticed about this year so far is that moisture may actually be overperforming relative to model forecasts from 3-5 days out, whereas in recent years it's often been the opposite).

The 500 mb pattern for Thursday evening, with the axis of the negative-tilt trough already swinging well out into the central/eastern Plains, reminds me a lot of some less-than-impressive days I've chased in the past few years. 2009-03-23 and 2008-11-05 come to mind. Both of those were 15% hatched tornado days along the I-35 corridor in OK/KS which basically didn't pan out. Here's hoping the thermodynamics on Thursday are enough better that we have a significantly different outcome.

As for the GFS/NAM vs. ECMWF timing and the associated placement of the cold front, I'd love to side with the latter, but it hasn't impressed me so far this year. Seems like more progressive has been the way to go.

 

[Jonathan Whitehead]

I wont go into a long forecast discussion but I will say that my biggest concern is quality of moisture return. This last sytem went clear through the Texas coast and scoured a bit of the moisture along the NWRN Gulf. I think well be lucky to see 62+ dews make it back in time. And if we do, its gonna be hella shallow. HOWEVER, it is possible that with the insane amount of shear/crossover that it overwhelms the modest moisture and we see a few tornadoes, ala April 20 in the Panhandle.

Overall Im not too impressed with this setup at this point but Im always biased toward higher dewpoints, at least thats what Id like to see anyway.

 

[Eric Bucsela]

The 500 mb pattern for Thursday evening, with the axis of the negative-tilt trough already swinging well out into the central/eastern Plains, reminds me a lot of some less-than-impressive days I've chased in the past few years. 2009-03-23 and 2008-11-05 come to mind.

Good points, Brett. This is in contrast to last Thursday's outbreak, when the strongest mid lvl flow was well SW of the Plains, and the flow aloft over CO, KS and TX was more diffluent. Surface and 850 winds were also much more backed. It's interesting that forecasts for the 1999 May 3 outbreak had almost meridional surface winds, although the surface flow verified more southeasterly (and that day obviously had other assets, including outstanding CAPE, etc).

Anyway, this setup is still 3 days away, and much can change.

 

[Melanie Metz]

I agree overall. Not too impressed yet. Need more moisture return, more instability. BUT 3 days is 3 days....which is why I rarely look that far ahead. I'm still hoping it will pan out better than it looks now!

Looking forward to those high Td and insane CAPE days later in the season! Much prefer that over the dynamics of the early spring.



Melanie

 

[Angie Norris]

Just finished taking a quick peek at the 0Z GFS, and I'm not overly impressed ATM. With unidirectional upper winds and slight backing at the surface, I would say we're looking at yet another squall line situation. Moisture is marginal, shear is weak. There appears to be a bit of a CAPE spike just south of the OKC metro at 0Z that could yield something of interest, but it's too soon to get too excited.