4/30/09 FCST: TX, OK, KS

[Randall Cooper]

As this is my first attempt at a forecast thread, please forgive me if its a little rough

I have been keeping an eye on Thursday for a few days now and I really think it holds some potential. NAM and GFS are in fairly good agreement in having 3000 J/kg CAPE across areas in OK, TX, and KS. It also has a good amount of moisture in that area as well. The only thing I would like to see change at this point a little bit are those 850 mb winds. Thoughts anyone?

 

[Eric Bucsela]

Glad this thread got started - I've also been watching Thursday. The models prog decent shear and excellent instability. Question is whether these parameters will overlap.

Looking at 72 hr GFS and NAM, both show best CAPEs - approaching 4000 - from southeast KS into much of OK. In the GFS, these CAPES are south of a fairly sharp frontal boudary from near Kansas City to Medicine Lodge, then westard to Liberal, where a dryline drops south into TX. In the NAM, the front is farther north and much less distinct (maybe from Concordia to Liberal) so that temps and dews are higher over most of KS - with highest CAPEs still confined to the extreme south (near ICT).

Problem is the good mid-level flow is way up in NEB and SD. In southern KS, the strongest 500 mb winds (all westerly) are only expected to be 20 kts - maybe 30 if you believe the NAM. 850 mb winds are so-so. The best are around 20 kts in OK and SE KS. Directional shear is pretty good.

So putting it all together, you'd have to compromise between the northern edge of the instability axis and the southern extent of the upper flow. The best play might be around Wichita and maybe northeastward towards Emporia, depending on how far south the front sags and whether it pushes the good surface air away from the upper support.

EDIT: Latest NAM (60 hr fcst) has moved things west, so south central-western KS (closer to the triple point) might be a better play. New GFS has also backed the front northward, with the best CAPE all in S.C. KS. Still not convinced the flow will be strong enough, but big CAPE - if it verifies - can do a lot.

 

[Greg McLaughlin]

I am keeping a close eye on THU. While mid-level flow is a little on the weak side (H5 winds of 30-35kts), the overall setup appears favorable for a nice supercell or two ahead of the dryline buldge and south of the front....somewhere around Medicine Lodge. You never know, we might get lucky and get an outflow boundary to set up somewhere from an overnight MCS. This definately will be worth watching.

 

[Michael O'Keeffe]

I agree with Greg the forecast sounding at Medicine Lodge looks pretty good with nice veering with height and some great CAPE and helicity to work with. Though the upper level flow may be a bit weak, the helicity may overcome that. Moisture will also be good so that won't be a concern. If this verifies there is a decent threat for supercells with very large hail and possibly some tornadoes, especially if a storm can ride the warm front.

 

[Justin Teague]

I am a huge fan of conditional set-ups like the one depicted by the models on Thursday. While there are several factors that could seemingly ruin the day, such as modest deep layer shear and weak anvil level winds.... I have had great success with similar set-ups.

I'm a little pessimistic about the forecasted strength of the surface low and associated dryline bulge but it's nice to see. While I suspect the WRF is over-doing the instability a bit, I do believe that MLCAPEs of ~3000 j/kg could be realized ahead of the dyrline bulge if it materializes. Strong to extreme instability could work to offset the weak upper flow and associated precip loading in the updrafts and I have seen this on several occasions. It's too far out to get any more specificss, but the set-up does appear favorable for 1 or 2 suprise supercells capable of producing the full spectrum of severe weather.

 

[Shane Adams]

If the advertised instability becomes reality, the weak shear won't matter much. 30kts at h5 will do on an average instability day, and if we see 3000-4000 j/kg THU, I think any storm that can form will be one that a bunch of people sitting in front of computers (that could've been there) will wish they were on. I like how there's barely any precip breaking out by 0Z, but by 3Z we're booming. That speaks of a stout cap (which will be needed for isolated development due to linear forcing along YET ANOTHER surging CF) and late-day initiation around 8pm or so.

Days like THU are what seperate the chasers from the SPCers.

 

[Brian Stertz]

My eyes are all over this one and am planning on taking a half day off to chase. Right now my initial target is Kingman KS. Although the flow is a bit weak and upper support lacking on the NAM forecasts, feel there are some other factors (namely strong directional shear, hardcore late April instability, and a decent boundary/low combo) that will counterbalance the weaknesses after about 7pm. I anticipate a fairly good evening chase before turning back to the northeast to KC in time for work Friday morning. This day will likely ring in as a SLIGHT risk unless some hidden ripple in the flow pops up in later runs. This is chaser primetime !!

 

[Chris Allington]

Now that the 00z runs are out I'm kinda on the fence with this one. 00z NAM is a little less bullish with the forecast CAPE values, and has some precip INVOF the boundary on and off throughout the day. GFS still has CAPE values peaking at 3500 j/kg+ in an area across the KS/OK border. While the flow is a little weak as other have mentioned, the CAPE values could definately make up for that some if he GFS were to play out, the actual directional profile is pretty decent and I like some of the model hodographs S of the Wichita area. Plus surface/ 850mb winds are very nicely backed just ahead of the low and right along the boundary. If I were too pick a target now I'd be departing Omaha around 9am to make the Clearwater, KS area around 3-3:30 as the cap looks to make it a fairly late show. However, I think I will review things through the day tomorrow, and if it continues to nudge a little further south I may scrap this one due to distance.

 

[Jeff House]

Thursday could be first day in a while without the risk of junk-vection on/near the target after 18z. Should still see pre-dawn and morning convection, which is good for boundary production, but it is out of there by 18z or sooner. Others have already made great points on the pros and cons, so I will limit my words. Nice plus Thu is a focused target where boundaries intersect, hopefully promoting more clear cut decision making vs say Sunday. Good luck!

 

[Eric Bucsela]

The 12z NAM and GFS now favor a more southern position for the front. Best CAPEs - still large - are in OK (NAM: 3000+ J/kg, GFS: 4000+ J/kg). But they've weakend the 850 wind field to the 10-20 kt range in OK. For a target in NW OK, 500 mb winds are progged at 20-30 kts, which is also marginal.

SPC is highlighting the KS/OK border for significant svr tomorrow. Where and what will depend on frontal position and how much of the instability is realized at initiation. May be a good day - I'd chase if I could!

EDIT: For perspective, storms today (4/29) were awesome, with only weak winds but good turning and CAPE.

 

[Jacob Ferden]

Wow, the 00z NAM is starting to reflect what the 18z GFS was showing over central Oklahoma: CAPE values in excess of 3500 J/kg by 00z Friday...hopefully the 00z GFS will continue the trend...could be a pretty good show from there northward to southern Kansas tomorrow if the models verify and the winds are at least decent. Right now I'm looking at a target somewhere in the I-35 corridor, probably the stretch between Guthrie and Braman, although that will likely change by morning.

 

[Brendon Lindsey]

The sounding for OUN is painting a pretty picture. SPC talks about a stout cap, but Sounding not really showing much of one... I like the Rain from I-40 South creating that Outflow boundary as the boundary extends ENE. I keep looking at the SKEW-Ts and I really believe a giganto Supercell can get going just NE of OKC, this is just going off the SKEW-T. Yeah if I was the spc I would be covering my butt too.

Edit: Well maybe there will be a cap... I do believe the rain went a little S and a little E than they believed it would...

 

[Greg McLaughlin]

Well it appears the great surprise day was yesterday. The setup today doesn't excite me at all. The wind fields are quite anemic, and the models have really backed off on developing a nice dryline (due to the lack of a surface low) in the eastern Texas panhandle. I am sure there will be outflow boundaries this afternoon, however you need more than just an outflow boundary to get a tornadic supercell. Typically, tornadic supercells associated with outflow boundaries tend to focus where the boundary intersects with the dryline. I don't see that happening today. I wish I could have made it out yesterday. We have had two outflow boundary tornado events so far this week and I have missed them both.

 

[Chris C Sanner]

While yesterday I was pretty sure that tornadoes would happen along the outflow boundaries if sufficient instability were to develop...I'm not as sure today with even weaker overall winds. However, the turning is still good and they still support supercell development. I'd say any storm forming on a boundary intersection and drifting (literally) S and SE would probably produce today in an environment of 3000+ CAPE...I'm eyeing several boundaries out there today and several intersections that they make...overall if a storm does produce this is a relatively easy day to chase given the extremely slow storm motions. You could probably almost chase them on foot or on a bicycle they'll be moving so slow

EDIT: I'm liking the intersection in NC Oklahoma....I'm probably heading out within the hour for that area...

 

[Greg McLaughlin]

I wish I hadn't made the previous post. Sometimes I can be a fool for the things I say. I just got home from work and have started looking things over in greater detail. I am beginning to really like the developing setup in central OK this afternoon.

Morning convection has pushed an outflow boundary west to roughly along the I-35 corridor. The boundary is oriented from the northwest to the southeast. This orientation is very favorable for a supercell to anchor on it given the 30kt H5 flow from the west-northwest. As the atmosphere continues to destabilize this afternoon in central OK I am hoping that enough convergence along the boundary will initiate a couple of storms and one of those storms can anchor on the boundary and do its thing.